Free download blueprints neurology 4th edition pdf

_www.cronistalascolonias.com.ar

10/9/08

PM

Page i

BLUEPRINTS

NEUROLOGY Third Edition

_www.cronistalascolonias.com.ar

10/9/08

PM

Page ii

_www.cronistalascolonias.com.ar

10/9/08

PM

Page iii

BLUEPRINTS

NEUROLOGY Third Edition

Frank W. Drislane, MD

Juan Acosta, MD

Associate Professor of Neurology Harvard Medical School Comprehensive Epilepsy Center Beth Israel Deaconess Medical Center Boston, Massachusetts

Neurologist, Clinical Neurophysiologist European Medical Doctor Best Doctors Madrid, Spain

Michael Benatar, MBChB, DPhil

Andrew Tarulli, MD

Associate Professor of Neurology and Epidemiology Director, Electromyography Laboratory Emory University Atlanta, Georgia

Instructor in Neurology Harvard Medical School Division of Neuromuscular Disease Beth Israel Deaconess Medical Center Boston, Massachusetts

Bernard S. Chang, MD

Louis R. Caplan, MD

Assistant Professor of Neurology Harvard Medical School Comprehensive Epilepsy Center Beth Israel Deaconess Medical Center Boston, Massachusetts

Professor of Neurology Harvard Medical School Cerebrovascular Service Beth Israel Deaconess Medical Center Boston, Massachusetts

_www.cronistalascolonias.com.ar

10/9/08

PM

Page iv

Acquisitions Editor: Charley Mitchell Managing Editor: Stacey Sebring and Jessica Heise Associate Production Manager: Kevin Johnson Creative Director: Doug Smock Compositor: Maryland Composition/ASI Printer: RR Donnelly Copyright © Frank W. Drislane, MD; Michael Benatar, MBChB, DPhil; and Bernard S. Chang, MD West Camden Street Baltimore, MD Walnut Street Philadelphia, PA All rights reserved. This book is protected by copyright. No part of this book may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner. The publisher is not responsible (as a matter of product liability, negligence, or otherwise) for any injury resulting from any material contained herein. This publication contains information relating to general principles of medical care that should not be construed as specific instructions for individual patients. Manufacturers’ product information and package inserts should be reviewed for current information, including contraindications, dosages, and precautions. Printed in China Library of Congress Cataloging-in-Publication Data Blueprints neurology / Frank W. Drislane [et al.]. — 3rd ed. p. ; cm. Includes bibliographical references and index. ISBN 1. Neurology—Examinations, questions, etc. 2. Physicians—Licenses—United States—Examinations—Study guides. I. Drislane, Frank. II. Title: Neurology. [DNLM: 1. Nervous System Diseases. 2. Neurology. WL B ] RCB —dc22 The publishers have made every effort to trace the copyright holders for borrowed material. If they have inadvertently overlooked any, they will be pleased to make the necessary arrangements at the first opportunity. To purchase additional copies of this book, call our customer service department at () or fax orders to () International customers should call () Visit Lippincott Williams & Wilkins on the Internet: www.cronistalascolonias.com.ar Lippincott Williams & Wilkins customer service representatives are available from am to pm, EST.

_www.cronistalascolonias.com.ar

10/9/08

PM

Page v

Contents Reviewers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vii Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii PART ONE: Basics of Neurology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 1 The Neurologic Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2 Neurologic Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PART TWO: Common Neurologic Symptoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The Approach to Coma and Altered Consciousness . . . . . . . . . . . . . . . . . . . 4 Neuro-Ophthalmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 The Approach to Weakness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 The Sensory System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Dizziness, Vertigo, and Syncope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Ataxia and Gait Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Urinary and Sexual Dysfunction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Headache and Facial Pain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PART THREE: Neurologic Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 11 Aphasia and Other Disorders of Higher Cortical Function . . . . . . . . . . . . . 12 Dementia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Sleep Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Vascular Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Seizures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Movement Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Head Trauma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Systemic and Metabolic Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Central Nervous System Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Demyelinating Diseases of the Central Nervous System . . . . . . . . . . . . . .

_www.cronistalascolonias.com.ar

10/9/08

PM

Page vi

vi • Contents

21 Infections of the Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Disorders of the Spinal Cord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 The Peripheral Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Disorders of the Neuromuscular Junction and Skeletal Muscle . . . . . . . 25 Pediatric Neurology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Answers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix: Evidence-Based Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

_www.cronistalascolonias.com.ar

10/9/08

PM

Page vii

Reviewers Catarina Castaneda, MD Class of Drexel University College of Medicine Philadelphia, Pennsylvania Maureen Chase, MD Resident, Emergency Medicine Hospital of University of Pennsylvania Jefferson Medical College Thomas Jefferson University Hospital Philadelphia, Pennsylvania Suzanne Crandall Class of Kansas City University of Medicine and Biosciences Kansas City, Missouri Alexis Dang, MD Class of University of California—San Francisco San Francisco, California Lee S. Engel, MD, PhD Fellow, Department of Infectious Diseases Louisiana State University Health Sciences Center New Orleans, Louisiana Merritt Fajt, MD Class of Temple University School of Medicine Philadelphia, Pennsylvania R1- Internal Medicine, Penn State University Milton S. Hershey Hershey Medical Center Hershey, Pennsylvania Baback Gabbay, MD Class of David Geffen School of Medicine at UCLA Los Angeles, California

_www.cronistalascolonias.com.ar

10/9/08

PM

Page viii

viii • Reviewers

Amir A. Ghaferi Class of Johns Hopkins School of Medicine Baltimore, Maryland Hoda Ghanem, MD Intern UC Irvine—Internal Medicine Irvine, California Sarah Harper Class of University of Pittsburgh School of Medicine Pittsburgh, Pennsylvania Gloria Hsu Class of Stanford University School of Medicine Stanford, California Mark Lassoff, MD Class of UMDNJ—New Jersey Medical School Newark, New Jersey Urology Resident LAC⫹USC Medical Center Los Angeles, California Ryan Ley Class of University of Nevada School of Medicine Reno, Nevada Meredith M. LeQuear, DO Class of New York College of Osteopathic Medicine Old Westbury, New York Mark Naftanel Class of Duke University School of Medicine Durham, North Carolina David J. Nusz, MD Class of SUNY Downstate College of Medicine Brooklyn, New York

_www.cronistalascolonias.com.ar

10/9/08

PM

Page ix

Reviewers • ix

Christi Otten Class of University of Oklahoma Health Sciences Center—Physician Assistant program Oklahoma City, Oklahoma Pulak Ray Class of University of Maryland School of Medicine Baltimore, Maryland Chris Reed Class of Medical College of Wisconsin Milwaukee, Wisconsin Matheni Sathananthan Class of SUNY at Buffalo School of Medicine Buffalo, New York Kamran Shamsa, MD Class of University of California—San Diego La Jolla, California Victor Sung Class of University of Texas Southwestern Medical Center Dallas, Texas Ahmet Tural, MD Department of Infectious Diseases Providence Physician Group Everett, Washington Alyssa Tzoucalis Class of Hofstra University—Physician Assistant program Hempstead, New York Parham Yashar, MD Neurological Surgery PGY-1 Albert Einstein College of Medicine Bronx, New York Ming Zhou, MD Class of University of Nevada School of Medicine Las Vegas, Nevada

_www.cronistalascolonias.com.ar

10/9/08

PM

Page x

x • Blueprints Psychiatry

Preface n , the first five books in the Blueprints series were published as board review for medical students, interns, and residents who wanted high-yield, accurate clinical content for USMLE Steps 2 and 3. Nearly a decade later, the Blueprints brand has expanded into a high-quality, trusted resource covering the broad range of clinical topics studied by medical students and residents during their primary, specialty, and subspecialty rotations. The Blueprints were conceived as study aids created by students, for students. In keeping with this concept, the editors of the current editions of the Blueprints books have recruited resident contributors to ensure that the third edition of the series continues to offer the information and approach that made the original Blueprints a success. Now in their third editions, each of the five specialty Blueprints—Blueprints Emergency Medicine, Blueprints Family Medicine, Blueprints Neurology, Blueprints Cardiology, and Blueprints Radiology—has been completely revised and updated to bring you the most current treatment and management strategies. The feedback we’ve received from our readers has been tremendously helpful in guiding the editorial direction of the second editions; for that, we are grateful to the hundreds of medical students and residents who have responded with in-depth comments and highly detailed feedback. Each book has been thoroughly reviewed and revised accordingly, with new features being included across the series. An evidence-based resource section has been added to provide current and classic references for each chapter, and an increased number of current board-format questions with detailed explanations for correct and incorrect answer options are included in each book. All revisions to the Blueprints series have been made in order to offer you the most concise, comprehensive, and cost-effective information available. Our readers report that Blueprints are useful for every step of their medical career, from their clerkship rotations and subinternships to a board review for USMLE Steps 2 and 3. Residents studying for USMLE Step 3 often use the books to review areas that were not their specialty. Students from a wide variety of health care specialties, including those in physician assistant, nurse practitioner, and osteopathic programs, use Blueprints either as a course companion or to review for their licensure examinations. However you use Blueprints, we hope that you find the books in the series informative and useful. Your feedback and suggestions are essential to our continued success.

I

The Publisher Lippincott Williams & Wilkins

_www.cronistalascolonias.com.ar

10/9/08

PM

Page xi

Acknowledgments e thank our patients for the opportunity of working with them and learning Neurology, our colleagues and teachers in the Beth Israel Deaconess Medical Center Neurology department for teaching us more fascinating concepts about the nervous system, and our families for tolerating the many hours spent writing and revising this book.

W

_www.cronistalascolonias.com.ar

10/9/08

PM

Page xii

xii • Blueprints Psychiatry

Abbreviations A(␤) ABP Abs A␤PP ACA ACE AD ADEM ADHD ADM AED AICA AIDP AIDS AION ALS ANA APP APS AVM AZT BMD BPPV CBC cGMP CIDP CJD CK CMAP CMT CN CNS COMT CP CPAP CSF CT DH DI DLB



DM DMD DSD DTRs DWI EA ED EEG EMG ER ESR ET EWN FDI FEV1 FLAIR FTA FTD FVC GAD GBS GCS GTC HD HIV HNPP HS HSAN HSV IBM ICA ICP ICU IIH INO INR IVIg LEMS LGN LMN



_www.cronistalascolonias.com.ar

10/9/08

PM

Page xiii

Abbreviations • xiii

LND LP MAG MCA MELAS



PM PML



_www.cronistalascolonias.com.ar

10/9/08

PM

Page xiv

_CHqxd

10/4/08

PM

Page 1

Part 1

Basics of Neurology

1

_CHqxd

10/4/08

PM

Page 2

_CHqxd

10/4/08

PM

Page 3

Chapter

1

The Neurologic Examination

To practicing neurologists, the neurologic exam reflects the uniqueness of the specialty. In a world of technology, it remains a purely clinical tool still unmatched in its ability to identify and localize abnormalities of the nervous system. To students, however, the exam can be both mystifying and bemusing, an endless series of maneuvers designed to elicit seemingly obscure and inexplicable findings. When its principles and elements are presented simply, though, the exam is logical and elegant, reflecting the rational diagnostic process that characterizes not just Neurology but all of medicine.

PRINCIPLES 1. The neurologic exam is not a standardized checklist. Part of the intimidation of performing the exam is its sheer length; hours could be spent on examining the mental status alone. In reality, however, the exam is used in a focused and thoughtful way, depending on what hypotheses have been generated about the patient’s disease from the history. A patient presenting with confusion may need quite a comprehensive mental status exam, whereas a patient presenting with a left foot drop may need detailed motor, sensory, and reflex testing of the left leg. In both cases general screening elements of the remaining parts of the exam may be sufficient. 2. Observation is more important than confrontation. Most abnormalities of the nervous system manifest themselves in ways visible to the observant examiner. A significant anomia becomes evident when a patient uses circumlocutions to relate the history, and proximal weakness is obvious

when they have difficulty rising from a chair. It is often more useful to describe a patient’s observed activities and capabilities than to describe the findings obtained upon formal testing. Confrontation testing is subjective and variable; the grading of muscle strength depends on the examiner’s effort and expectations of what the patient’s “normal” strength should be. The observation of a pronator drift, for example, is less subjective. 3. The object is to localize. The extent and complexity of the nervous system require that any attempt to formulate a concise differential diagnosis must begin with an accurate localization of the problem to a specific region of the nervous system. Left hand weakness may stem from carpal tunnel syndrome, a brachial plexus injury, cervical spondylosis, or a right middle cerebral artery stroke, all of which have different diagnostic workups, treatments, and prognoses. The alert physician thinks, “What signs would be present in a carpal tunnel problem that would not be present in a brachial plexus problem (and vice versa)?” Those signs are then sought and the exam further refined if necessary. 4. Not all findings have equal importance. A common difficulty is that completion of the exam results in a long list of many minor abnormalities of questionable importance, such as a 20% decrease in temperature sensation over a patch on the left thigh. Though certainly in some cases incidental findings may be the clue to a previously unsuspected diagnosis, in most cases the highest importance must be given to findings directly related to the patient’s symptoms and to “hard” findings that require definitive explanation, such as a dropped reflex or a Babinski sign. 3

_CHqxd

10/4/08

PM

Page 4

4 • Blueprints Neurology

ELEMENTS OF THE EXAM

KEY POINTS • The neurologic exam is not a standardized checklist. • Observation is more important than confrontation. • The object is to localize. • Not all findings have equal importance.

䊏

As discussed earlier, the specific features to include in the neurologic exam should vary with each patient; however, commonly performed elements of the exam are described in this section and listed in Table

TABLE Commonly Performed Elements of the Neurologic Examination

Mental status Attention

Serial backward tasks (months of the year, digit span)

Language

Fluency of speech, repetition, comprehension of commands, naming objects, reading, writing

Memory

Three words in 5 minutes

Visuospatial function

Drawing clock, copying complex figure

Neglect

Line bisection, double simultaneous stimulation

Frontal lobe function

Generating word lists, learning a motor sequence

Cranial nerves II

Visual acuity, fields, pupils, funduscopic exam

III, IV, VI

Extraocular movements

V, VII

Facial sensation and movement

IX, X, XII

Palate and tongue movement

Motor Bulk

Palpation for atrophy

Tone

Evaluation for rigidity, spasticity

Power

Observational tests (pronator drift, rising from chair, walking on heels and toes), direct confrontation strength testing

Reflexes Muscle stretch reflexes

Biceps, brachioradialis, triceps, knee, ankle

Babinski sign

Stroking lateral sole of foot

Sensory Pinprick and temperature

Pin, cold tuning fork

Vibration and joint position sense

Tuning fork and moving digits

Coordination Accuracy of targeting

Finger-to-nose, heel-to-shin

Rhythm of movements

Rapid alternating movements, rhythmic finger or heel tapping

Gait Stance

Narrow or wide base

Romberg sign

Steadiness with feet together and eyes closed

Stride and arm swing

Assessment for shuffling, decreased arm swing

Ataxia

Ability to tandem walk

_CHqxd

10/4/08

PM

Page 5

Chapter 1 / The Neurologic Examination • 5

MENTAL STATUS Neurologists use the mental status exam to identify cognitive deficits that help to localize a problem to a specific region of the brain. Thus the exam differs from that used by psychiatrists, whose objectives in performing the exam are different. The first step in mental status testing is to assess the level of consciousness. This may vary from the alert wakefulness of a clinic outpatient to the coma of a patient in the intensive care unit. There is a tendency to use “medical” terminology—such as stuporous, obtunded, or lethargic—to describe the level of consciousness, but these have variable meanings; it is more useful to describe how well patients stayed awake or what stimulation was required to arouse them. Next, assuming the level of consciousness allows for further testing of cognitive functions, attention is tested, typically with serial forward and backward tasks. These include digit span, reciting the months of the year, or spelling the word “world,” all forward and backward. Attention is usually tested early, because significant inattention compromises the ability to perform subsequent cognitive tests and may render their interpretation difficult. Next, language is assessed. As noted previously, listening to the patient tell their history may be all that is necessary to gauge language ability. Formal testing, however, includes assessing the fluency of spontaneous speech, the ability to repeat, the ability to comprehend commands, the ability to name both common and less common objects, and the ability to read and write. For memory testing, most often the patient is given three words and asked to recall them several minutes later, with the aid of hints if necessary. More information can be gained by giving longer lists of words and charting the patient’s learning (and forgetting) curve. Visual memory can be tested with three simple shapes for the patient to draw from memory in several minutes. Visuospatial function can be tested in a variety of ways. Patients can be asked to draw a clock, a cube, or another simple figure; alternatively, they can be asked to copy a complex figure drawn by the examiner (Fig. ). Neglect is a mental status finding typically not sought by nonneurologists, yet its presence can be a very important sign. Patients with dense neglect may fail to describe items on one side of a picture or of their surroundings, or may fail to bisect a line properly. Subtle neglect may manifest as extinction to double simultaneous stimulation, in which a patient

Figure • Example of a complex figure to be copied by the patient as test of visuospatial function.

can sense a single stimulus on either side but when bilateral stimuli are presented simultaneously will sense only the one on the nonneglected side. Tests of frontal lobe function include learning a simple motor sequence of hand postures, inhibiting inappropriate responses when following a “go/no-go” paradigm, or generating lists of words beginning with a particular letter or belonging to a particular category.

KEY POINTS • The mental status exam should begin with assessment of level of consciousness and attention, because these can affect the interpretation of subsequent tests. • Language, memory, visuospatial function, neglect, and tests of frontal lobe function are other key elements of the mental status exam that can suggest focal brain lesions.

CRANIAL NERVES It is usually easiest to test the cranial nerves (or at least to record the results) in approximate numerical order (Table ). Olfaction (cranial nerve I) is rarely tested, but when this is important, each nostril should be tested separately with a nonnoxious stimulus, such as coffee or vanilla. Tests of optic nerve (II) function include visual acuity (using a near card), visual fields (tested by confrontation with wiggling fingers or with a small red

_CHqxd

10/4/08

PM

Page 6

6 • Blueprints Neurology

䊏

TABLE The Cranial Nerves

Nerve

English Name

Exit Through Skull

Function

I

Olfactory

Cribriform plate

Olfaction (test using nonnoxious substance)

II

Optic

Optic canal

Vision (acuity, fields, color), afferent limb of pupillary reflex

III

Oculomotor

Superior orbital fissure

Superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae, efferent limb of pupillary reflex

IV

Trochlear

Superior orbital fissure

Superior oblique (of contralateral eye)

V

Trigeminal

Superior orbital fissure (V1), foramen rotundum (V2), foramen ovale (V3)

Muscles of mastication, tensor tympani, tensor veli palatini, facial sensation, afferent limb of corneal reflex

VI

Abducens

Superior orbital fissure

Lateral rectus

VII

Facial

Internal auditory meatus

Muscles of facial expression, stapedius, taste on anterior two-thirds of tongue, efferent limb of corneal reflex

VIII

Vestibulocochlear

Internal auditory meatus

Hearing, vestibular function

IX

Glossopharyngeal

Jugular foramen

Movement of palate, sensation over palate and pharynx, taste over posterior one-third of tongue, afferent limb of gag reflex

X

Vagus

Jugular foramen

Movement of palate, sensation over pharynx, larynx, and epiglottis, efferent limb of gag reflex, parasympathetic function of viscera

XI

Accessory

Jugular foramen

Sternocleidomastoid and trapezius movement

XII

Hypoglossal

Hypoglossal foramen

Tongue movement

object, which is more sensitive), and the pupillary light reflex, the afferent limb of which is mediated by this nerve. Funduscopic examination is the only means by which a part of the central nervous system (the retina) can be directly visualized. Extraocular movements (III, IV, and VI) are tested in three ways: by having the patient pursue a moving target that is a drawing of the letter “H” in front of their face (pursuit), by directing their gaze rapidly to various stationary targets (saccades), and by fixating on an object while the head is being turned passively (vestibulo-ocular movements). The presence of nystagmus should be noted. Muscles of mastication (V) are tested by assessing strength of jaw opening and palpating over the masseters bilaterally while the jaw is clenched. Facial sensation can be tested to all modalities over the forehead (V1), cheek (V2), and jaw (V3). The afferent limb of the corneal reflex is mediated by this nerve. Muscles of facial expression (VII) are tested by having patients raise their eyebrows, squeeze their eyes shut, or show their teeth. Though uncommonly tested, taste over the anterior two-thirds of the

tongue is mediated by this nerve and can be evaluated with sugar or another nonnoxious stimulus. Hearing (VIII) may be evaluated in each ear simply by whispering or rubbing fingers; more detailed assessment of hearing loss may be accomplished with the Weber or Rinne tuning fork ( Hz) test. Vestibular function can be tested in many ways, including evaluation of eye fixation while the patient’s head is rapidly turned or by observation for drift in one direction while the patient is walking in place with the eyes closed. Palatal elevation should be symmetric and the voice should not be hoarse or nasal (IX and X). Failure of the right palate to elevate implies pathology of the right glossopharyngeal nerve. The gag reflex is also mediated by these nerves. Sternocleidomastoid strength is tested by having the patient turn the head against resistance; weakness on turning to the left implies a right accessory nerve (XI) problem. The trapezius muscle is tested by having the patient shrug their shoulders. Tongue protrusion should be in the midline. If the tongue deviates toward the right, the problem lies with the right hypoglossal nerve (XII).

_CHqxd

10/4/08

PM

Page 7

Chapter 1 / The Neurologic Examination • 7

KEY POINTS • Cranial nerve testing is most easily performed and recorded in approximate numerical order. • Key elements of the cranial nerve exam include assessment of vision and eye movements, facial movement and sensation, and movements of the palate and tongue.

MOTOR EXAM The motor exam includes more than just strength testing—in fact, strength should usually be the portion of the exam performed last. First, bulk is assessed by observing and palpating the muscles and comparing each side to the other and

the patient’s overall muscle bulk to that expected for age. The presence of fasciculations or of adventitious movements such as tremor or myoclonus should also be noted. Tone is one of the most important parts of the motor exam. In the upper extremities, tone is checked by moving the patient’s arm at the elbow in both flexion-extension and circular movements, by moving the wrist in a circular fashion, and by rapidly pronating and supinating the forearm using a handshake grip. Abnormalities of tone such as spasticity and rigidity are discussed in subsequent chapters. Tone in the lower extremities can be tested well only with the patient supine. The examiner lifts the leg up suddenly under the knee; only in the presence of increased tone will the heel come off the bed. Finally, strength or power is assessed, by both functional observation and direct confrontation (Fig. ).

Figure • Power testing of individual movements. For each movement, the predominant muscle, peripheral nerve, and nerve root are given. (Reproduced with permission from Ginsberg L. Lecture Notes: Neurology, 8th ed. Oxford: Blackwell Publishing, –)

_CHqxd

10/4/08

PM

Page 8

8 • Blueprints Neurology

䊏

TABLE Medical Research Council Grading of Muscle Power 0

No contraction of muscle visible

1

Flicker or trace of contraction visible

2

Active movement at joint, with gravity eliminated

3

Active movement against gravity

4

Active movement against gravity and some resistance

5

Normal power

A pronator drift may be observed in an arm held supinated and extended in front of the body. The patient may be asked to rise from a chair without using the arms or to walk on the heels or toes. The power of individual muscles assessed by direct confrontation testing is graded according to the Medical Research Council (MRC) scale (Table ), although refinements of the scale (such as the use of 4⫺, 4, and 4⫹) or the use of a point scale will increase precision.

Figure • Muscle stretch (“deep tendon”) reflexes.

KEY POINTS

(Reproduced with permission from Ginsberg L. Lecture Notes: Neurology, 8th ed. Oxford: Blackwell Publishing, )

• The motor exam begins with assessment of bulk and tone. • Abnormalities of increased tone include both spasticity and rigidity. • Strength testing involves both functional observation as well as confrontation testing of individual muscle’s power. • Strength is graded on the MRC scale from 0 to 5.

In the lower extremities, patellar (knee jerk) and ankle reflexes are the ones commonly tested. The adductor reflex can also be tested. The Babinski sign is sought by stroking the lateral sole of the foot while observing for extension of the great toe. Clonus, if present, can be elicited by forcibly dorsiflexing the ankle when it is relaxed.

SENSORY EXAM REFLEXES Muscle stretch (or “deep tendon”) reflexes can be useful aids in localizing or diagnosing both central and peripheral nervous system problems (Fig. ). In the upper extremities, the biceps, brachioradialis, and triceps reflexes are the ones commonly tested. Pectoral and finger flexor reflexes can also be tested. Hoffmann’s sign is sought by flicking the distal phalanx of the middle finger while observing for flexion of the thumb.

The sensory exam can be frustrating to perform because of the tedium of potentially examining the entire body surface (see dermatome map in Chapter 6) as well as the inherent subjectivity and all-toofrequent inconsistencies in patients’ responses. In general, sensation should be tested in detail in areas relevant to a patient’s complaints, especially if the complaints are sensory in nature. Otherwise, screening elements of the sensory exam that are targeted at the distal lower extremities, where most

_CHqxd

10/4/08

PM

Page 9

Chapter 1 / The Neurologic Examination • 9

asymptomatic sensory abnormalities are likely to be found, may be sufficient. Pinprick sensation is tested with a safety pin, the sharp edge of a broken-off cotton swab, or special pins designed for the neurologic exam. Temperature sensation, mediated by the same pathway, is most easily tested with the side of a tuning fork, which, if freshly retrieved from an instrument bag, will be quite cold on the skin. Vibration is tested by striking the Hz tuning fork and placing its stem against the joint being tested, typically beginning at the toes. Joint position sense, or proprioception, is tested beginning most distally by holding the patient’s great toe by its sides and moving it slightly upward or downward. Light touch is the least useful modality to test, because it is carried by a combination of pathways and is unlikely to provide clues to localization or diagnosis.

KEY POINTS • The sensory exam is usually the most subjective portion of the neurologic exam. • In a patient without sensory complaints, screening elements of the sensory exam that are targeted at the distal extremities may be sufficient. • Pinprick and temperature are carried in one pathway; vibration and joint position sense in another.

COORDINATION This portion of the exam, often incorrectly referred to as “cerebellar” testing, in fact serves to test coordinated movements whose successful completion requires the interaction of multiple components of the motor system, not just the cerebellum. Finger-to-nose testing can identify the presence of dysmetria (inaccuracy of targeting) or intention tremor. Heel-to-shin testing can elicit incoordination in the lower extremities. Rapid alternating movements, rhythmic finger tapping, and heel tapping are particularly sensitive to coordination problems. Patients may have trouble with the timing or cadence of these movements. Dysdiadochokinesis is the term used to describe difficulty with rapid alternating movements.

GAIT Aside from orthopedic surgeons, neurologists are among the only doctors to routinely test a patient’s gait, yet the “normal” function of walking requires the proper functioning of so many different aspects of the nervous system that it is frequently a sensitive way to detect an abnormality. In addition, certain diseases, such as Parkinson disease, have quite distinctive gaits associated with them. The patient with a normal stance maintains the feet at an appropriately narrow distance apart; a wide-based stance is abnormal. The Romberg sign is present when the patient maintains a steady stance with feet together and eyes open but sways and falls with feet together and eyes closed. Its presence usually implies a deficit of joint position sense, not cerebellar function, as is commonly believed. Stride length should be full. Short-stepped or shuffling gaits are characterized by a decrease in stride length and clearance off the ground. Ataxia of gait results in an inability to walk in a straight line; patients may stagger from one side to the other or consistently list toward one side. Ataxia is typically associated with a wide-based stance. Ataxia can be brought out most obviously by having the patient attempt tandem gait, walking heel to toe. The arms normally swing in the opposite direction from their respective legs during ambulation. Decreased arm swing is a feature of extrapyramidal disorders. Finally, difficulty initiating ambulation or understanding the appropriate motor program for walking, leaving the feet “stuck to the floor” despite intact motor and sensory function, characterizes the gait of frontal lobe dysfunction, sometimes referred to as gait apraxia. Hydrocephalus is one etiology of such a gait disorder.

KEY POINTS • Gait is one of the most important elements of the neurologic exam because it is sensitive for many deficits, and certain diseases have characteristic gait disorders. • Stance, stride length, arm swing, ability to tandem walk, and initiation of walking should all be assessed in the gait exam. • The Romberg sign suggests a deficit in joint position sense.

_CHqxd

10/4/08

PM

Page 10

Chapter

2

Neurologic Investigations

CEREBROSPINAL FLUID ANALYSIS Cerebrospinal fluid (CSF) bathes the internal and external surface of the brain and spinal cord. It is produced by the choroid plexus of the ventricles and absorbed through the villi of the arachnoid granulations that project into the dural venous sinuses. CSF is produced continually at a rate of about mL per minute; the total volume is approximately mL. The entire CSF volume is thus replaced about every 5 hours. Lumbar puncture (LP) via the L interspace is the most commonly used means of obtaining CSF for analysis. LP is contraindicated by the presence of a space-occupying lesion that is causing mass effect, raised intracranial pressure, or local infection or inflammation at the planned puncture site.

TECHNIQUE LP is best performed with the patient in the lateral recumbent position with the legs flexed up over the abdomen. Optimal positioning is the key to a successful and atraumatic LP. Ideally, a pillow should be placed between the legs, and the patient should lie on the edge of the bed where there is better support to keep the back straight. The anterosuperior iliac spine is at the level of the L vertebral interspace. The LP may be performed at this level, one interspace higher, or one to two interspaces lower. Remember that the spinal cord ends at the level of L The needle is inserted with the bevel facing upward, so that it will enter parallel to the ligaments and dura that it pierces rather than cutting them transversely. The needle is directed slightly rostrally to coincide with the downward angulation of the spinous processes. The needle 10

is advanced gently until CSF is obtained. To measure the opening pressure reliably, the patient’s legs should be extended slightly and note should be made of fluctuation of the CSF meniscus within the manometer with respiration.

INTERPRETATION OF RESULTS CSF is a clear, colorless fluid. The glucose content is about two-thirds that of blood, and it contains up to 40 to 50 mg/dL protein. Fewer than five cells are present, and these are lymphocytes. Measured by LP in the lateral recumbent position, the opening pressure is about 60 to mm H2O. Xanthochromia refers to the yellow discoloration of the supernatant of a spun CSF sample. Its presence helps to distinguish an in vivo intrathecal hemorrhage from a traumatic tap [in which red blood cells (RBCs) have not lysed and the supernatant is still colorless]. The implications of various CSF findings are summarized in Table The CSF findings in a variety of common conditions are summarized in Table Special tests may be performed as indicated. Some examples include cytology for suspected malignancy, oligoclonal banding for suspected immune-mediated processes such as multiple sclerosis, 14,3,3-protein for Creutzfeldt-Jakob disease, and a variety of polymerase chain reactions and serologic tests for various infections.

SAFETY, TOLERABILITY, AND COMPLICATIONS Cerebral or cerebellar herniation may occur when lumbar puncture is performed in the presence of

_CHqxd

10/4/08

PM

Page 11

Chapter 2 / Neurologic Investigations • 11

䊏

TABLE Interpretation of CSF Findings

Red blood cells No xanthochromia

Traumatic tap

Xanthochromia

Subarachnoid hemorrhage; hemorrhagic encephalitis

White blood cells Polymorphs

Bacterial or early viral infection

Lymphocytes

Infection (viral, fungal, mycobacterial); demyelination (MS, ADEM); CNS lymphoma

Elevated protein

Infection (fungal, mycobacterial); demyelination; tumor (e.g., meningioma, carcinomatous meningitis); sarcoidosis; age

Low glucose

Bacterial infection; mycobacterial infection

Oligoclonal bands

Demyelination (MS); CNS infections (e.g., Lyme disease); noninfectious inflammatory processes (e.g., SLE)

Positive EBV PCR

Highly suggestive of CNS lymphoma in patients with AIDS or other immunosuppressed states

ADEM, acute disseminated encephalomyelitis; AIDS, acquired immunodeficiency syndrome; CNS, central nervous system; EBV PCR, Epstein-Barr virus polymerase chain reaction; MS, multiple sclerosis; SLE, systemic lupus erythematosus.

either a supratentorial or infratentorial mass lesion. A computed tomography (CT) scan should be performed prior to an LP except in cases of suspected meningitis and when a CT scan cannot be performed. Radiologic contraindications to LP include closure of the fourth ventricle and quadrigeminal

䊏

cistern. Low-pressure headache is the most common complication of lumbar puncture and is most effectively treated by having the patient lie flat and increase her intake of liquids and caffeine. Rarely, it may be necessary to administer an epidural blood patch (see Chapter 10).

TABLE CSF Findings in Common Neurologic Diseases

Disease

Cells (pleocytosis)

Protein

Glucose

Other

Bacterial meningitis

Polymorphs

High

Low

Culture and Gram stain may be positive

Viral meningitis/encephalitis

Lymphocytes

High

Normal

Viral PCR may be positive

Tuberculous meningitis

Lymphocytes

High

Very low

Positive for acid-fast bacilli

Guillain-Barré syndrome

None

High (degree depends on interval from symptom onset)

Normal

—

MS

Few lymphocytes

Slightly high

Normal

OCBs usually present

ADEM

Lymphocytes or polymorphs

Usually high

Normal

OCBs usually absent

Subarachnoid hemorrhage

Lymphocytes and many red blood cells

May be high

Normal

Xanthochromia

ADEM, acute disseminated encephalomyelitis; MS, multiple sclerosis; OCB, oligocional bands.

_CHqxd

10/4/08

PM

Page 12

12 • Blueprints Neurology

KEY POINTS • A CT scan should be performed prior to lumbar puncture except when bacterial meningitis is suspected. • Lumbar puncture is performed at or below the L interspace. • Xanthochromia indicates recent intrathecal hemorrhage.

COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING TECHNICAL CONSIDERATIONS CT measures the degree of x-ray attenuation by tissue. Attenuation is defined simply as the removal (by absorption or scatter) of x-ray photons and is quantified on an arbitrary scale (in Hounsfield units) that is represented in shades of gray. Differences in the shades directly reflect the differences in the x-ray attenuation of different tissues, a property that depends on their atomic number and physical density. Images are usually obtained in either an axial or a coronal plane. Three-dimensional reconstruction and angiography are possible with new-generation spiral CT scanners. Magnetic resonance imaging (MRI) is similar to CT in that radiant energy is directed at the patient and detected as it emerges from the patient. MRI differs, however, in its use of radiofrequency (RF) pulses rather than x-rays. The images in MRI result from the varying intensity of radio-wave signals emanating from tissue in which hydrogen ions have been excited by an RF pulse. A detailed understanding of magnetic resonance physics is not necessary for the interpretation of routinely used MRI sequences. It is sufficient to understand that the patient is placed in a magnet and that an RF pulse is administered. Signal intensity is measured at a time interval, known as time to echo (TE), following RF administration. The RF pulse is administered many times in generating an image; the time to repetition (TR) is the time between these RF pulses. Two basic MRI sequences in common usage are T1- (short TE and TR) and T2- (long TE and long TR) weighted images. Fat is bright on a T1-weighted image, which imparts a brighter signal to the myelincontaining white matter. Water (including CSF) is dark on T1 and bright on T2. T2 images are most

Figure • T2-weighted MRI of the cervical spine.

useful in evaluating the spinal cord (Fig. ). Gadolinium is the contrast agent used in MRI, and gadolinium-enhanced images are usually acquired with a T1-weighted sequence. Contrast-enhanced images are invaluable in determining the presence of brain tumors, abscesses, other areas of inflammation, and new multiple sclerosis lesions (see Fig. ). Other commonly used MRI sequences are fluidattenuated inversion recovery (FLAIR) and susceptibility- and diffusion-weighted imaging (DWI). FLAIR is a strong T2-weighted image, but one in which the signal from CSF has been inverted and is thus of low rather than high intensity. FLAIR is the single best screening image sequence for most pathologic processes of the central nervous system (CNS). It is very useful in assessing the chronic lesion burden in multiple sclerosis (see Fig. ). A susceptibility-weighted sequence is one that is sensitive to the disruptive effect of a substance on the local magnetic field. Examples of substances that exert such a susceptibility effect are calcium, bone, and the blood breakdown products ferritin and hemosiderin. Areas of increased susceptibility appear black on these images. DWI demonstrates cellular toxicity with high sensitivity and is most commonly employed in the diagnosis of acute stroke, where it can be positive within half an hour of symptom onset. Areas of restricted

_CHqxd

10/4/08

PM

Page 13

Chapter 2 / Neurologic Investigations • 13

Figure • Normal T1, T2, FLAIR, and DWI images of the brain.

diffusion appear bright on DWI. Figure provides examples of T1, T2, FLAIR, and DWI images.

CLINICAL UTILITY Head CT is often the initial investigation used in a variety of neurologic disorders, including headache, trauma, seizures, subarachnoid hemorrhage, and stroke. The sensitivity of a CT scan for detecting lesions depends on many factors, including the nature and duration of the underlying disease process. The sensitivity for detecting areas of inflammation, infection, or tumor may be increased by the administration of intravenous contrast. Contrast enhancement indicates local disruption of the blood-brain barrier. CT is the investigation of choice for demonstrating fresh blood. Apart from providing better anatomic definition, MRI is particularly useful for imaging the contents of the posterior fossa and craniocervical junction, which are seen poorly on CT because of artifact from surrounding bone. DWI is the most sensitive technique

available for demonstrating early tissue ischemia and is therefore extremely useful in the evaluation of patients with suspected stroke.

SAFETY, TOLERABILITY, AND COMPLICATIONS CT scanning employs x-rays and is thus relatively contraindicated during pregnancy. The use of RF waves in MRI makes this the imaging modality of choice in pregnant women. There is no cross-reactivity between the iodinated contrast agents used in CT and the gadolinium used as a contrast agent in MRI. When contrasted imaging is required, MRI may therefore be preferable when there is a history of allergy to intravenous contrast. Similarly, gadolinium does not have the nephrotoxicity of iodinated contrast. MRI may be used safely only in the absence of metal objects (foreign bodies, plates, and screws) and pacemaker and defibrillator devices. Some people with claustrophobia cannot tolerate MRI; under these circumstances, CT is preferred.

_CHqxd

10/4/08

PM

Page 14

14 • Blueprints Neurology

KEY POINTS • CT is the imaging modality of choice for demonstrating acute intracranial bleeding. • MRI is required for adequate imaging of the posterior fossa and craniocervical junction. • DWI is the most sensitive MRI sequence for demonstrating early cerebral ischemia or infarction.

VASCULAR IMAGING STUDIES Conventional angiography involves cannulation of the great vessels and injection of contrast dye to obtain an image of the vascular anatomy (Fig. ). This is the most sensitive and specific imaging study of the intracranial and extracranial circulation. Risks of the procedure include contrast dye reaction, stroke due to plaque dislodged by the catheter, and bleeding from the cannulation site. Although the risks of the procedure, and developments in magnetic resonance angiography (MRA) (below), have decreased the number of conventional angiograms performed, it remains the “gold standard” in vascular imaging. MRA uses blood flow as a contrast agent and MR technique to define vascular anatomy (Fig. ).

Figure • MRA of the circle of Willis.

Compared with conventional angiograpy, MRA is less invasive and can be performed more quickly and less expensively, but it is not as sensitive or specific for cerebrovascular disease. MRA is performed commonly on the intracranial circulation of stroke patients to look for evidence of vascular narrowing or occlusion. “Fat-suppressed” MRA of the neck is useful for determining the presence of vertebral or carotid artery dissections. Magnetic resonance venography (MRV) can be used to demonstrate venous sinus thrombosis and other venous disease. Extracranial Doppler sonography measures blood flow by determining the difference between emitted and received ultrasound frequencies. It is used commonly to detect stenosis or occlusion of the extracranial carotid circulation, especially in the planning stages for carotid endarterectomy. Transcranial Doppler (TCD) detects intracranial stenosis and emboli. Most of the intracranial circulation, however, is inaccessible to TCD. Although somewhat less accurate than MRA or conventional angiography, Doppler studies are noninvasive and virtually without contraindication.

KEY POINTS • Conventional angiography is the gold standard for evaluating cerebrovascular anatomy.

Figure • Conventional cerebral angiogram demonstrating aneurysm of the right middle cerebral artery (arrow). (Reproduced with permission from Patel PR. Lecture Notes: Radiology, 2nd ed. Oxford: Blackwell Publishing, )

• MRA is less invasive but also less accurate than conventional angiography. • MRV is useful for assessing the presence of venous sinus thrombosis.

_CHqxd

10/4/08

PM

Page 15

Chapter 2 / Neurologic Investigations • 15

OTHER IMAGING STUDIES Positron emission tomography (PET) scans measure regional brain metabolism. Hypermetabolism can be demonstrated during seizures (though it is rare to get the scan during a seizure), while hypometabolic regions may be evident interictally. Such a finding can be very useful in planning epilepsy surgery, especially in the temporal areas. Single-photon emission computed tomography (SPECT) uses a radioactive isotope to demonstrate increased blood flow during seizures. Both PET and SPECT scans have been studied in the evaluation of dementia. While regional patterns of abnormality help study disease processes, they are not specific enough for diagnosis in individual patients. Magnetic resonance spectroscopy is primarily a research tool used to demonstrate areas of neuronal damage or dysfunction and has been studied in the assessment of brain tumors, demyelinating disease, and infections of the CNS.

ELECTROENCEPHALOGRAPHY The electroencephalogram (EEG) provides a record of the electrical activity of the cerebral cortex. Normal EEG patterns are characterized by the frequency and amplitude of the recorded electrical activity, and the patterns of activity correlate with the degree of wakefulness or sleep. The normally observed frequency patterns are divided into four groups: alpha (8 to 13 Hz), beta (14 to 30 Hz), theta (4 to 7 Hz), and delta ( to Hz) (Fig. ). Under normal circumstances, alpha waves are observed over the posterior head

Figure • Electroencephalographic frequencies.

regions in the relaxed awake state with the eyes closed. Lower-amplitude beta activity is more prominent over the frontal regions. Theta and delta activity is normal during drowsiness and sleep, and the different stages of sleep are defined by the relative proportions and amplitudes of theta and delta activity (see Chapter 13).

TECHNIQUE The standard EEG is recorded from electrodes attached to the scalp in a symmetric array. The pattern in which these electrodes are connected to each other is referred to as the montage, of which there are essentially two types: bipolar and referential. In a bipolar montage, all electrodes are active and a recording is made of the difference in electrical activity between two adjacent electrodes. In a referential montage, the electrical activity is recorded beneath the active electrode relative to a distant electrode or common average signal. The signal recorded by an EEG is a sum of excitatory and inhibitory postsynaptic potentials of cortical neurons.

CLINICAL UTILITY To appreciate the utility of the EEG, it is important to understand its limitations. First, the patterns of electrical activity recorded by the EEG are rarely (if ever) specific to their cause. For example, the presence of diffuse theta or delta activity during the awake state suggests an encephalopathy but does not indicate the etiology. Second, the EEG records the electrical activity of cortical neurons. Although subcortical structures influence cortical activity, the surface EEG may be insensitive to dysfunction of deep structures. For example, seizures originating in the medial frontal or temporal lobes may not be readily apparent on the surface EEG. Furthermore, the EEG provides a measure of the electrical activity of the cortex at the time of the recording and is therefore frequently normal in paroxysmal conditions such as seizures. The interictal EEG, for example, may be abnormal in only about 50% of adults with epilepsy. The frequency of interictal EEG abnormalities may be higher in certain forms of epilepsy. Several common patterns of abnormal activity are recognized. Focal arrhythmic or polymorphic slow activity in the theta or delta range suggests local dysfunction in the underlying brain. Vascular disease is a common cause of such findings, but the slowing

_CHqxd

10/4/08

PM

Page 16

16 • Blueprints Neurology

cannot specify the etiology. Generalized arrhythmic slow activity often indicates a diffuse encephalopathy. Interictal epileptiform findings include sharpand spike-wave discharges, with or without an accompanying slow wave. Electrographic seizures may take various forms. The most common are rhythmic spike- or sharp- and slow-wave discharges or rhythmic slow waves. They may be focal or generalized. Activation procedures can be used to enhance the likelihood of finding abnormal EEG patterns: hyperventilation is useful for provoking EEG changes in patients with absence seizures, while photic stimulation can induce EEG changes in patients with myoclonic seizures.

KEY POINTS • Alpha frequency (8 to 13 Hz) is the dominant posterior rhythm on the EEG in the awake restful state with the eyes closed. • Epilepsy is a clinical diagnosis; interictal epileptiform EEG findings are demonstrable in about half of patients with epilepsy.

NERVE CONDUCTION STUDIES AND ELECTROMYOGRAPHY Nerve conduction studies (NCS) and electromyography (EMG) are appropriately used as an extension of the clinical examination.

are placed over the endplate of a muscle innervated by the nerve being stimulated. The nerve is stimulated in at least two locations (distal and proximal), and the distance between the two sites of stimulation is measured carefully. The distal latency, compound muscle action potential (CMAP), and conduction velocity are recorded. The CMAP is a recording of the contraction of the underlying muscle. The distal latency is the time interval between stimulation over the distal portion of the nerve and the initiation of the CMAP. Conduction velocity is calculated by measuring the difference in latency to CMAP initiation between proximal and distal sites of stimulation. For sensory studies, the nerve is stimulated at one site and the sensory nerve action potential (SNAP) is recorded either at a more proximal site (orthodromic study) or at a more distal site (antidromic study). Repetitive nerve-stimulation studies are used to demonstrate either decremental or incremental CMAP responses in disorders of the neuromuscular junction. Electromyography involves the insertion of a needle into individual muscles. Recordings are made of the muscle electrical activity upon insertion (insertional activity), while the muscle is at rest (spontaneous activity), and during contraction (volitional motor unit potentials). To increase the strength of muscular contraction, motor units can fire more quickly (activation) or more motor units can be added (recruitment). Reduced activation is seen in CNS disease. Reduced recruitment suggests a lower motor neuron lesion, while early recruitment can be seen in myopathic disease. For routine EMG studies, activity is recorded from a group of muscle fibers simultaneously. Singlefiber EMG is the technique used in the investigation of disorders of the neuromuscular junction.

TECHNIQUE CLINICAL UTILITY In performing NCS, an electrical stimulus is applied over a nerve and recordings are made from surface skin electrodes. For motor studies, the recording electrodes 䊏

NCS and EMG are used primarily to assist in the localization of dysfunction within the peripheral

TABLE Electromyography in Neurogenic and Myopathic Disorders Neurogenic

Myopathic

Insertional activity:

↑ (active denervation)

Usually normal ↑ (necrotizing myopathies)

Spontaneous activity:

↑ (active denervation)

Usually normal ↑ (necrotizing myopathies)

Volitional motor unit potentials: Recruitment:

Large amplitude; polyphasic Reduced

Small amplitude; polyphasic Usually normal early

_CHqxd

10/4/08

PM

Page 17

Chapter 2 / Neurologic Investigations • 17

䊏

TABLE Nerve Conduction Studies in Demyelinating and Axonal Neuropathies Demyelinating

Axonal

Distal latency:

Markedly prolonged

Normal, or mildly prolonged

Conduction velocity:

Markedly reduced

Normal; may be slightly slowed

CMAP amplitude:

Normal or mildly reduced

Reduced

CMAP, compound muscle action potential.

nervous system and to define pathophysiology more clearly. For example, NCS and EMG may help to differentiate a C8–T1 radiculopathy from a lower brachial plexopathy or an ulnar neuropathy in the patient who presents with numbness of the fourth and fifth fingers and weakness of the hand. Similarly, the combination of motor NCS, repetitive nerve stimulation, and EMG may help to localize motor dysfunction (i.e., weakness) to the peripheral nerve, the neuromuscular junction, or the muscle (Table ). In a patient with a polyneuropathy, NCS may help to define the relative degree of motor and sensory involvement and to

distinguish primary demyelinating from axonal disease (Table ).

KEY POINTS • The goal of NCS and EMG is to localize the neurologic dysfunction within the peripheral nervous system. • Repetitive nerve stimulation and single-fiber EMG are useful in the diagnosis of disorders of the neuromuscular junction.

_CHqxd

10/4/08

PM

Page 18

_CHqxd

10/4/08

PM

Page 19

Part 2

Common Neurologic Symptoms

19

_CHqxd

10/4/08

PM

Page 20

_CHqxd

10/4/08

Chapter

3

PM

Page 21

The Approach to Coma and Altered Consciousness

The neurologic evaluation and management of a patient with coma or altered consciousness can be intimidating for the student, because such patients are usually critically ill and may require prompt intervention. The fundamental principles behind the evaluation of a neurologic problem, however, should not be discarded. On the contrary, an orderly and hypothesis-based approach may be even more important in a comatose patient than in others, given the need for timely diagnosis and the relative limitations on history and examination.

KEY POINTS • Coma is a state of unarousable unresponsiveness. • It is important to describe a patient’s responses to various degrees of stimulation. • The Glasgow Coma Scale, which has prognostic value in patients with head trauma, is reproducible and easy to use.

CLINICAL APPROACH DEFINITION Coma is defined as a state of unarousable unresponsiveness. Typically the patient lies with eyes closed and does not open them even to vigorous stimulation, such as sternal rub, nasal tickle, or nailbed pressure. Alterations in consciousness short of coma are often described using terms such as drowsiness, lethargy, obtundation, and stupor, but these terms tend to be used imprecisely and it is generally best to describe simply how the patient responded to various degrees of stimulation. The Glasgow Coma Scale assigns a numerical score to a patient’s level of responsiveness and is commonly used by neurosurgeons in cases of head trauma (see Table ). Its utility lies in its ease of use by nurses and paramedics, its interrater reproducibility, and its prognostic value following head injury.

An algorithm for approaching patients with coma or altered consciousness is presented in Figure The initial steps of stabilization and evaluation culminate in the neurologic exam, which is performed with two goals in mind: to assess brainstem function and to look for focal signs. The differential diagnosis and further investigations stem from this clinical assessment. 1. Remember the ABCs. In any patient with altered consciousness, the airway, breathing, and circulation should be checked and maintained according to usual protocols, including intubation and mechanical ventilation if required. 2. Look for obvious clues to etiology. A brief history and general exam should be performed to search for obvious clues. A history of medical problems

21

_CHqxd

10/4/08

PM

Page 22

22 • Blueprints Neurology

Remember the ABCs

Look for obvious clues to etiology • Brief history • General exam • Meningeal signs

Try reversing common reversible etiologies • Naloxone • Thiamine • Dextrose

Use the neurologic exam • to check brainstem reflexes • to look for focal signs

Focal signs present

Suspect structural cause • Urgent neuroimaging • Different diagnosis in Table

Focal signs absent

Suspect diffuse cause • Metabolic, toxic, and/or infectious workup • Neuroimaging • Differential diagnosis in Table

Figure • The approach to coma and altered consciousness.

such as diabetes, hepatic failure, alcoholism, or a seizure disorder may be provided by the family, noted on a medical alert bracelet, or deduced from prescription labels. The circumstances in which the patient was found can offer clues to the onset or etiology of depressed consciousness. The general exam may yield telling signs, such as an odor on the breath, needle tracks on the skin, or a tongue laceration. It is important to check for meningeal signs in any unconscious patient because both bacterial meningitis and subarachnoid hemorrhage may lead to depressed consciousness.

3. Try reversing common reversible etiologies. Most emergency rooms (ERs) make it standard practice to administer naloxone, thiamine, and dextrose to any patient with depressed consciousness and no obvious etiology. Note that thiamine should always be given before glucose, because the latter can precipitate Wernicke encephalopathy if given alone. 4. Check brainstem reflexes and look for focal signs. These are the two primary goals of the neurologic exam in this setting, because the subsequent diagnostic and therapeutic steps will depend on these clinical findings.

_CHqxd

10/4/08

PM

Page 23

Chapter 3 / The Approach to Coma and Altered Consciousness • 23

KEY POINTS • The clinical approach to the patient with altered consciousness begins with the ABCs: airway, breathing, and circulation. • Look for obvious clues to etiology. • Try reversing common reversible etiologies. • Use the neurologic exam to check brainstem reflexes and look for focal signs.

EXAMINATION It is important to proceed with the neurologic exam of a comatose patient in an orderly fashion—it is easy to be intimidated or distracted by the array of attached tubes and lines or by the intensity and anxiety of other clinicians. An appropriate way to begin is to progress systematically through the sequence of the usual neurologic exam, making adjustments as necessary for the patient’s altered level of responsiveness. Mental status testing in these patients begins with assessing the level of consciousness. An increasing gradient of stimulation should be applied and the patient’s responses recorded. For example, does the patient lie with his or her eyes closed but open them slowly when spoken to in a loud voice? Does he or she groan but not open his or her eyes when sternal rub is applied? For many patients, further cognitive testing may not be possible. For those who can be aroused 䊏

even briefly, however, a short evaluation of attention, language, visuospatial function, and neglect is in order, because this may reveal a gross focal finding such as an aphasia or dense neglect of the left side. Cranial nerves should be examined in detail, because this is the portion of the exam most relevant to the assessment of brainstem function. In an arousable patient, most cranial nerves can be tested in the usual manner. In a patient who is not arousable enough to follow commands, several important brainstem reflexes should be tested (Table ), including the pupillary, corneal, oculocephalic, and gag reflexes. In addition, a funduscopic examination should always be performed. For many patients with altered consciousness, testing for a blink to visual threat may be the only way to judge visual fields. If the patient cannot move his or her face to command, the examiner may be restricted to looking for an asymmetry at rest, such as a flattened nasolabial fold on one side. The presence of an endotracheal tube may make such observation difficult. Motor tone should be checked in all extremities. If the patient can cooperate with some testing, a gross hemiparesis can be ruled out by having the patient hold the arms extended or legs elevated and observing for downward drift. Otherwise, the examiner may be restricted to observing for asymmetry of spontaneous movements (or to asking caretakers whether all extremities have been seen to move equally). Failing that, noxious stimuli such as nailbed pressure or a pinch on a flexor surface can be applied

TABLE Brainstem Reflexes

Reflex

Cranial Nerves Involved

How to Test

Pupillary

II (afferent); III (efferent)

Shine light in each pupil and observe for direct (same side) and consensual (contralateral side) constriction

Oculocephalic (doll’s eyes)

VIII (afferent); III, IV, VI (efferent)

Forcibly turn head horizontally and vertically and observe for conjugate eye movement in opposite direction (contraindicated if cervical spine injury has not been ruled out)

Caloric testing (if necessary)*

Same

Inject 50 mL ice water into each ear and observe for conjugate eye deviation toward the ear injected

Corneal

V1 (afferent); VII (efferent)

Touch lateral cornea with cotton tip and observe for direct and consensual blink

Gag

IX (afferent); X/XI (efferent)

Stimulate posterior pharynx with cotton tip and observe for gag

*Caloric testing should be performed if turning the head is contraindicated or does not result in eye movement. Never assume the eyes are immobile unless caloric testing has been done.

_CHqxd

10/4/08

PM

Page 24

24 • Blueprints Neurology

DIFFERENTIAL DIAGNOSIS

Figure • Decorticate (above) and decerebrate (below) posturing in response to noxious stimuli. Both indicate brainstem dysfunction, although decorticate posturing suggests dysfunction slightly more superior than decerebrate posturing. (Reproduced with permission from Kandel ER, Schwatz JH, Jessell TM. Principles of Neural Science, 4th ed. New York: McGraw-Hill, )

to each limb and the speed and strength of withdrawal noted, although abnormalities here may result from sensory loss as well as motor dysfunction. Decorticate and decerebrate posturing, signs of brainstem dysfunction, may be seen either spontaneously or in response to noxious stimuli (Fig. ). Muscle stretch reflexes can be tested in the usual manner, and a Babinski sign should be sought. Sensory testing in most patients with altered consciousness is limited to testing of light touch or pain sensation. Noxious stimulation to each limb, as described previously, may be useful in looking for gross sensory abnormalities. Coordination and gait may be tested in patients who are arousable enough.

In theory, there are two main ways in which consciousness can be depressed: the brainstem can be dysfunctional or both cerebral hemispheres can be dysfunctional simultaneously. In fact, acute disease in the brainstem (e.g., pontine hemorrhage) can lead to coma, as can processes affecting both cerebral hemispheres at once (e.g., hypoglycemia). Unilateral cerebral hemispheric lesions, however, can also lead to coma if they are large or severe enough to cause swelling and compression of the opposite hemisphere or downward pressure on the brainstem. Therefore most neurologists interpret the information obtained from the exam of the comatose patient using the following principle: the presence or absence of brainstem reflexes suggests how deep the coma is, while the presence or absence of focal signs narrows the differential diagnosis and guides the workup. Thus, in milder cases of depressed consciousness, the pupillary, corneal, and gag reflexes may all be preserved. In more severe cases, some or all of these brainstem reflexes may be lost, no matter what the etiology. (Note that if a brainstem reflex is abnormal in an asymmetric fashion, such as a unilateral unreactive pupil, this would be interpreted as a focal sign and suggests compression of or primary disease in the brainstem.) The presence of focal signs either on cranial nerve testing or in the remainder of the examination— including such findings as hemiparesis, aphasia, reflex asymmetry, facial droop, or a unilateral Babinski sign—suggests a structural cause of depressed consciousness (Box ). Examples include a large unilat䊏 BOX Structural Causes of Depressed

Consciousness Acute ischemic stroke Brainstem

KEY POINTS • The mental status exam in patients with altered consciousness primarily assesses the level of responsiveness. • The cranial nerve exam includes the testing of important brainstem reflexes, including the pupillary, corneal, and oculocephalic reflexes. • The remainder of the examination should be dedicated to looking for focal abnormalities.

Unilateral cerebral hemisphere (with edema) Acute intracranial hemorrhage Intraparenchymal Subdural Epidural Brain tumor (with edema or hemorrhage) Primary Metastatic Brain abscess

_CHqxd

10/4/08

PM

Page 25

Chapter 3 / The Approach to Coma and Altered Consciousness • 25

eral stroke or intracranial hemorrhage. The absence of focal signs suggests a diffuse cause of depressed consciousness, including metabolic, toxic, or hypoxicischemic etiologies (Box ). Examples include coma from fulminant hepatic failure, barbiturate overdose, or anoxia following prolonged cardiac arrest.

KEY POINTS

䊏 BOX Diffuse Causes of Depressed

Consciousness Metabolic Electrolyte abnormality Hyponatremia, hypernatremia, hypocalcemia, hypercalcemia, hypomagnesemia, hypermagnesemia, hypophosphatemia Glucose abnormality Hypoglycemia, nonketotic hyperosmolar coma, diabetic ketoacidosis

• In theory, consciousness can be depressed either by dysfunction of the brainstem or dysfunction of both cerebral hemispheres simultaneously; in reality, large unilateral hemispheric lesions (with pressure on the other side) qualify as well.

Hepatic failure

• The presence or absence of brainstem reflexes suggests how deep the coma is.

Thyroid dysfunction Myxedema coma, thyrotoxicosis

• The presence of focal signs suggests a structural cause of coma.

Adrenal insufficiency

• The absence of focal signs suggests a diffuse cause of coma, such as metabolic, toxic, infectious or hypoxic-ischemic etiologies.

Uremia

Toxic Alcohol Sedatives Narcotics Psychotropic drugs

LABORATORY AND RADIOGRAPHIC STUDIES The distinction between structural and diffuse causes of depressed consciousness, arrived at by interpreting the findings on exam, suggests different pathways of diagnostic workup. The presence of focal findings on examination, suggesting a structural cause, demands urgent head imaging, almost always a noncontrast computed tomography (CT) scan. One should be looking for signs of a large acute stroke, an intracranial hemorrhage, or a mass lesion that may have enlarged rapidly or had hemorrhage within it. (Contrast-enhanced CT should be avoided if acute hemorrhage is possible.) Even in cases where focal brainstem signs are found, the initial choice of head imaging may have to be a CT scan rather than magnetic resonance imaging (MRI), despite the poor quality of the former in evaluating the brainstem, because of the possibility of a large cerebral hemispheric lesion compressing the brainstem as well as because of the more immediate availability of CT. The absence of focal findings on examination, suggesting a diffuse cause, warrants an extensive workup for causes of metabolic, toxic, or infectious etiologies. Blood testing—including complete blood count (CBC), electrolytes, glucose, liver function tests, and

Other exogenous toxins (carbon monoxide, heavy metals) Infectious Meningitis (bacterial, viral, fungal) Diffuse encephalitis Hypoxic-ischemic Respiratory failure Cardiac arrest Other Subarachnoid hemorrhage Carcinomatous meningitis Seizures or postictal state

toxicologic screen—may be necessary. If infection is suspected, a chest x-ray, urinalysis, and blood or urine cultures may be called for. There should be a low threshold for obtaining a lumbar puncture (LP). If a basic workup is unrevealing, one should search for more unusual causes (such as myxedema coma, by checking thyroid function tests). Head imaging is usually needed even in these cases of suspected diffuse cause because it may demonstrate signs of global hypoxic-ischemic injury, diffuse cerebral edema, or bilateral lesions mimicking a diffuse

_CHqxd

10/4/08

PM

Page 26

26 • Blueprints Neurology

process, although the urgency is not as high as for patients with focal findings. Of course, a head CT should be performed before obtaining an LP almost without exception in the evaluation of a patient with depressed consciousness, given the risk of precipitating brain herniation if a large intracranial mass (particularly in the posterior fossa) is present. (If bacterial meningitis is suspected, empiric antibiotic treatment can be started if CT scanning is delayed.) Frequently, an electroencephalogram (EEG) is ordered in patients with coma or altered consciousness. Although many of its findings may be nonspecific, the EEG can help to assess how deep a coma is based on the degree of background slowing. In addition, there are occasionally more specific patterns on EEG that suggest a particular diagnosis, such as hepatic encephalopathy or anoxic brain injury. Finally, the EEG can rule out nonconvulsive status epilepticus as a cause of coma in cases in which this is (or is not) clinically suspected.

KEY POINTS • If a structural cause of coma is suspected, urgent head imaging, usually with a noncontrast head CT, should be performed. • If a diffuse cause is suspected, an extensive workup for metabolic, toxic, or infectious causes should be undertaken. • Head imaging in suspected diffuse cases may demonstrate cerebral edema, signs of global hypoxic-ischemic injury, or bilateral lesions mimicking a diffuse process.

hemorrhages, Chapter 17 for head trauma, Chapter 18 for systemic and metabolic disorders, Chapter 19 for brain tumors, and Chapter 21 for central nervous system (CNS) infections. When increased intracranial pressure (ICP) is suspected clinically or radiographically, treatments aimed at lowering ICP should be applied. These include raising the head of the bed, hyperventilation, and the use of an osmotic diuretic such as mannitol. Corticosteroids tend to be useful only in cases of edema associated with brain tumors. The lowering of ICP may be a neurologic or neurosurgical emergency if the patient shows signs of brain herniation, which is discussed in more detail in Chapter The prognosis of depressed consciousness is mostly dependent on etiology—the patient with a barbiturate overdose may recover completely, whereas one with a severe anoxic injury likely will not. Age is an important prognostic factor as well. One of the most frequent reasons for admission to an intensive care unit (ICU) or neurologic consultation is to estimate the prognosis of a patient in coma following cardiopulmonary arrest. In these cases the circumstances and duration of the arrest are important, and published studies have correlated outcome with findings on neurologic examination performed at least 24 hours after the arrest.

KEY POINTS • The treatment of coma or altered consciousness depends on etiology.

• Almost without exception, head CT should be performed before LP.

• The lowering of intracranial pressure may be a neurologic emergency if the patient shows signs of brain herniation.

• EEG can assess the depth of coma and can occasionally suggest a specific diagnosis.

• Prognostic factors for coma or altered consciousness include both etiology and patient age.

TREATMENT AND PROGNOSIS

SPECIAL TOPICS

The treatment of coma and altered consciousness rests on the specific diagnosis. Metabolic, infectious, or toxic etiologies require mostly medical management, while some structural causes of coma may require neurosurgical intervention. Specific treatments for particular conditions are detailed in later chapters, in particular Chapter 14 for strokes and

PERSISTENT VEGETATIVE STATE Persistent vegetative state is a state in which patients have lost all awareness and cognitive function but may remain with their eyes open, exhibit sleep-wake cycles, and maintain respiration and other autonomic functions. Patients may progress into this state after

_CHqxd

10/4/08

PM

Page 27

Chapter 3 / The Approach to Coma and Altered Consciousness • 27

being in coma for a prolonged period if their vital functions have been supported.

LOCKED-IN SYNDROME Although a locked-in syndrome can be confused with coma at first glance, a patient with locked-in syndrome is awake and may be intact cognitively, with no abnormality of consciousness. Usually a consequence of large lesions in the base of the pons, the locked-in syndrome leaves patients unable to move the extremities and most of the face. If all other motor function is lost, they may be limited to communicating by vertical eye movements or blinks.

BRAIN DEATH Death can be declared either when there has been irreversible cessation of cardiopulmonary function or there has been irreversible cessation of all functions of the entire brain, including the brainstem. A declaration of death based on the latter criterion is commonly referred to as brain death. Many institutions have specific guidelines for how brain death must be determined, but in general the patient must be comatose, have absent brainstem reflexes, and have no spontaneous respirations even when the PCO2 has been allowed to rise (the apnea test). Confounding factors such as hypothermia or drug overdose must not be present. Confirmatory tests most commonly include an EEG, which can demonstrate electrocerebral silence (“flat line”), or cerebral angiography, which can demonstrate absence of blood flow to the brain. Local institutional guidelines for declaration of brain death should always be consulted.

KEY POINTS • A persistent vegetative state may follow prolonged coma and is characterized by preserved sleep-wake cycles and maintenance of autonomic functions, with absence of awareness and cognition. • Locked-in syndrome, in which awareness and cognitive function are preserved but almost complete paralysis occurs, is often caused by large lesions in the base of the pons. • Brain death is a declaration of death based on irreversible cessation of all brain functions.

ACUTE CONFUSIONAL STATE Definition The terms confusion, delirium, and encephalopathy are often used nonspecifically to indicate a disturbance of mental status in which the patient is unable to carry out a coherent plan of thought or action. Most neurologists employ the terms confusion or encephalopathy, while delirium (commonly used by psychiatrists) often implies a state of encephalopathy characterized by a waxing and waning level of alertness. At its core, an acute confusional state results from a problem of attention. Thus, a patient’s failure to answer questions in a coherent manner or to carry out an intended series of actions in an expected way derives from an inability to maintain attention for long enough to proceed through the cognitive or motor steps required for the task. On formal mental status testing, therefore, patients with confusion typically do poorly on standard tests of attention, such as spelling the word “world” in reverse, reciting the months of the year backward, or completing serial subtractions. Such inattention may be significant enough to make impossible the performance of more detailed mental status testing. Depending on the underlying etiology of the acute confusional state, other associated features may be present on neurologic or general physical examination as well.

Differential Diagnosis The differential diagnosis of acute confusion includes a number of different disorders, among them aphasia (particularly Wernicke), psychosis, and complex partial seizures. Patients with Wernicke aphasia may appear “confused” but in fact are attentive and able to carry out coherent series of actions; their deficit lies solely in their ability to communicate. Although patients with psychosis may also behave as if they were acutely confused, pure confusional states do not result in frank psychotic symptoms like hallucinations or delusions. Complex partial seizures can be characterized by behavior that appears “confused,” but seizures are typically self-limited in duration and may be associated with clonic motor movements or automatisms such as lip-smacking.

_CHqxd

10/4/08

PM

Page 28

28 • Blueprints Neurology

Diagnostic Evaluation

Treatment and Prognosis

An acute confusional state is most commonly caused by an underlying systemic or neurologic disorder, including infection, metabolic disturbance, inflammatory condition, or hypoxic-ischemic state, among many possibilities. Focal brain disorders, particularly acute right hemispheric lesions, can also lead to confusion. The appropriate diagnostic workup in a patient with confusion is therefore potentially quite extensive. Blood work and urinalysis to search for infectious or metabolic disturbances are often warranted. If there is clinical suspicion for a CNS infection, cerebrospinal fluid (CSF) analysis should be performed. Neuroimaging should be obtained if the neurologic history or examination suggests the possibility of an acute focal lesion. An EEG can help to determine whether there is a widespread dysfunction (encephalopathy) or focal abnormalities. It is unlikely to demonstrate the precise cause of an acute confusional state but can help to confirm a diagnosis, since characteristic findings of an encephalopathy may be present.

The treatment and prognosis of acute confusional states depend largely on the underlying etiology. Most cases of confusion arise from a reversible underlying cause and will resolve if the underlying disorder is treated appropriately. Confusional states arising from structural neurologic lesions or more chronic underlying disturbances may be less likely to improve spontaneously.