Jasper R. Daube, MD, and Devon I. Rubin, MD, Editors
76 PERIPHERAL NEUROPATHIES IN CLINICAL PRACTICE
Steven Herskovitz, MD, Stephen N. Scelsa, MD, and Herbert H. Schaumburg, MD
77 CLINICAL NEUROPHYSIOLIOGY OF THE VESTIBULAR SYSTEM
Fourth Edition
Robert W. Baloh, MD, FAAN, and Kevin A. Kerber, MD
78 THE NEURONAL CEROID LIPOFUSCINOSES (BATTEN DISEASE)
Second Edition
Sara E. Mole, PhD, Ruth D. Williams, MD, and Hans H. Goebel, MD, Editors
79 PARANEOPLASTIC SYNDROMES
Robert B. Darnell, MD, PhD, and Jerome B. Posner, MD
80 JASPER’S BASIC MECHANISMS OF THE EPILEPSIES
Jeffrey L. Noebels, MD, PhD, Massimo Avoli, MD, PhD, Michael A. Rogawski, MD, PhD, Richard W. Olsen, PhD, and Antonio V. Delgado-Escueta, MD
81 MYASTHENIA GRAVIS AND MYASTHENIC DISORDERS
Second Edition
Andrew G. Engel, MD
82 MOLECULAR PHYSIOLOGY AND METABOLISM OF THE NERVOUS SYSTEM
Gary A. Rosenberg, MD
83 SEIZURES AND EPILEPSY
Second Edition
Jerome Engel, Jr., MD, PhD
84 MULTIPLE SCLEROSIS
Moses Rodriguez, MD, Orhun H. Kantarci, MD, and Istvan Pirko, MD
85 FRONTOTEMPORAL DEMENTIA
Bruce L. Miller, MD
86 AUTONOMIC NEUROLOGY
Eduardo E. Benarroch, MD
87 EVALUATION AND TREATMENT OF MYOPATHIES
Second Edition
Emma Ciafaloni, MD, Patrick F. Chinnery, FRCP, FMedSci, and Robert C. Griggs, MD, Editors
88 MOTOR NEURON DISEASE IN ADULTS
Mark Bromberg, MD
89 HYPERKINETIC MOVEMENT DISORDERS
Roger M. Kurlan, MD, Paul E. Green, MD, and Kevin M. Biglan, MD, MPH
90 THE NEUROLOGY OF EYE MOVEMENTS
Fifth Edition
R. John Leigh, MD, FRCP, and David S. Zee, MD
91 MIGRAINE
Third Edition
David W. Dodick, MD, and Stephen D. Silberstein, MD, FACP, FAHS, FAAN
92 CLINICAL NEUROPHYSIOLOGY, Fourth Edition
Devon Rubin, MD and Jasper Daube, MD, Editors
93 NEUROIMMUNOLOGY
Bibiana Bielekova, MD, Gary Birnbaum, MD, and Robert P. Lisak, MD, FRCP
94 PLUM AND POSNER’S DIAGNOSIS AND TREATMENT OF STUPOR AND COMA
Fifth Edition
Jerome B. Posner, MD, Clifford B. Saper, MD, PhD, Nicholas D. Schiff, MD, and Jan Claassen, MD, PhD
CLINICAL NEUROPHYSIOLOGY
Fifth Edition
Edited by Devon I. Rubin Professor of Neurology Director, EMG Laboratory Mayo Clinic Jacksonville, Florida
1
Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and certain other countries.
Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016, United States of America.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by license, or under terms agreed with the appropriate reproduction rights organization. Inquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above.
You must not circulate this work in any other form and you must impose this same condition on any acquirer.
Library of Congress Cataloging-in-Publication Data
Names: Rubin, Devon I., editor.
Title: Clinical neurophysiology / [edited by] Devon I. Rubin.
Description: 5th edition. | New York, NY : Oxford University Press, [2021] |
Series: Contemporary neurology series ; 95 | Includes bibliographical references and index.
Identifiers: LCCN 2020052816 (print) | LCCN 2020052817 (ebook) | ISBN 9780190067854 (hardback) | ISBN 9780190067878 (epub) | ISBN 9780190099923
Subjects: MESH: Nervous System Diseases—diagnosis | Nervous System Diseases—therapy | Electroencephalography | Electromyography | Evoked Potentials | Neurophysiology
LC record available at https://lccn.loc.gov/2020052816
LC ebook record available at https://lccn.loc.gov/2020052817
DOI: 10.1093/med/9780190067854.001.0001
This material is not intended to be, and should not be considered, a substitute for medical or other professional advice. Treatment for the conditions described in this material is highly dependent on the individual circumstances. And, while this material is designed to offer accurate information with respect to the subject matter covered and to be current as of the time it was written, research and knowledge about medical and health issues is constantly evolving and dose schedules for medications are being revised continually, with new side effects recognized and accounted for regularly. Readers must therefore always check the product information and clinical procedures with the most up- to- date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulation. The publisher and the authors make no representations or warranties to readers, express or implied, as to the accuracy or completeness of this material. Without limiting the foregoing, the publisher and the authors make no representations or warranties as to the accuracy or efficacy of the drug dosages mentioned in the material. The authors and the publisher do not accept, and expressly disclaim, any responsibility for any liability, loss, or risk that may be claimed or incurred as a consequence of the use and/ or application of any of the contents of this material. Links to third party websites are provided by Oxford in good faith and for information only. Oxford disclaims any responsibility for the materials contained in any third party website referenced in this work.
9 8 7 6 5 4 3 2 1
Printed by Integrated Books International, United States of America
Preface xi
Acknowledgments xiii
List of Contributors xv
INTRODUCTION 1
SECTION I BASIC NEUROPHYSIOLOGY
1. BASICS OF NEUROPHYSIOLOGY 9
Devon I. Rubin
2. ELECTROPHYSIOLOGICAL GENERATORS IN CLINICAL NEUROPHYSIOLOGY 41
Terrence D. Lagerlund
3. WAVEFORMS AND ARTIFACTS 47
Devon I. Rubin
SECTION II CLINICAL ELECTROENCEPHALOGRAPHY
ADULT EEG
4. ADULT ELECTROENCEPHALOGRAPHY: NORMAL AND BENIGN VARIANTS 65
23. TECHNICAL ISSUES AND POTENTIAL COMPLICATIONS OF NERVE CONDUCTION STUDIES 431
Devon I. Rubin
NEEDLE ELECTROMYOGRAPHY
24. NEEDLE ELECTROMYOGRAPHY 451
Devon I. Rubin
25. QUANTITATIVE ELECTROMYOGRAPHY 495
Benn E. Smith
26. SINGLE-FIBER ELECTROMYOGRAPHY 525
Brian A. Crum and C. Michel Harper Jr.
27. TECHNICAL PROBLEMS AND POTENTIAL COMPLICATIONS OF NEEDLE EMG 549
Devon I. Rubin
APPLICATIONS OF ELECTROMYOGRAPHY
28. ELECTRODIAGNOSTIC ASSESSMENT OF MONONEUROPATHIES 559
Julie A. Khoury
29. ELECTRODIAGNOSTIC ASSESSMENT OF RADICULOPATHIES 579
Jaimin S. Shah
30. ASSESSMENT OF PLEXOPATHIES 591
Elliot L. Dimberg
31. ELECTRODIAGNOSTIC ASSESSMENT OF POLYNEUROPATHIES 603
Michelle L. Mauermann
32. ELECTRODIAGNOSTIC ASSESSMENT OF MOTOR NEURON DISEASES 619
Nathan P. Staff
33. ASSESSMENT OF NEUROMUSCULAR JUNCTION DISEASES 627
Elie Naddaf
34. ELECTRODIAGNOSTIC ASSESSMENT OF MYOPATHIES 639
Teerin Liewluck
35. NEUROMUSCULAR ELECTRODIAGNOSTIC TESTING IN THE INTENSIVE CARE UNIT 653
Brent P. Goodman
36. NEUROMUSCULAR ULTRASOUND IN THE EMG LABORATORY 665
Andrea J. Boon
37. SOMATOSENSORY EVOKED POTENTIALS 683
James C. Watson and Devon I. Rubin
38. VISUAL EVOKED POTENTIALS 719
Jonathan L. Carter
39. BRAINSTEM AUDITORY EVOKED POTENTIALS 733
Jonathan L. Carter
40. MOTOR EVOKED POTENTIALS 747
Elizabeth A. Mauricio
SECTION V ASSESSMENT OF AUTONOMIC FUNCTION
41. AUTONOMIC PHYSIOLOGY 763
William P. Cheshire Jr.
42. QUANTITATIVE SUDOMOTOR AXON REFLEX AND RELATED TESTS 775
Phillip A. Low and Elizabeth A. Coon
43. EVALUATION OF ADRENERGIC FUNCTION 781
Phillip A. Low and Wolfgang Singer
44. THERMOREGULATORY SWEAT TEST 789
Robert D. Fealey
45. CARDIOVAGAL REFLEXES 807
Elizabeth A. Coon and William P. Cheshire Jr.
SECTION VI CLINICAL NEUROPHYSIOLOGY OF MOVEMENT DISORDERS
46. MOVEMENT-RELATED CORTICAL POTENTIALS AND EVENT-RELATED POTENTIALS 825
Rene L. Utianski and John N. Caviness
47. LONG LATENCY REFLEXES AND THE SILENT PERIOD 833
Anhar Hassan and John N. Caviness
48. ELECTROPHYSIOLOGY TESTING OF MOVEMENT DISORDERS 845
Bryan T. Klassen, John N. Caviness, and James H. Bower
SECTION VII ASSESSMENT OF SLEEP
49. ASSESSMENT OF SLEEP AND SLEEP DISORDERS: POLYSOMNOGRAPHY AND OTHER TESTS 871
Michael H. Silber and Cameron D. Harris
50. PEDIATRIC SLEEP ASSESSMENT 895
Suresh Kotagal
51. ABNORMAL SLEEP AND SLEEP DISORDERS 905
Erik K. St. Louis and Mithra R. Junna
SECTION VIII INTRAOPERATIVE MONITORING
52. CEREBRAL FUNCTION MONITORING AND CORTICAL MAPPING FOR NONEPILEPSY SURGERY 925
Elson L. So and E. Matthew Hoffman
53. BRAINSTEM AND CRANIAL NERVE MONITORING 943
Iryna M. Muzyka and E. Matthew Hoffman
54. SPINAL CORD AND ROOT MONITORING 957
E. Matthew Hoffman
55. PERIPHERAL NERVOUS SYSTEM MONITORING 977
Iryna M. Muzyka, Jeffrey A. Strommen, and C. Michel Harper Jr.
SECTION IX ELECTRICAL CONCEPTS AND SAFETY
56. VOLUME CONDUCTION IN CLINICAL NEUROPHYSIOLOGY 1001
Terrence D. Lagerlund and Devon I. Rubin
57. INSTRUMENTATION AND ELECTRICITY FOR CLINICAL NEUROPHYSIOLOGY 1019
Terrence D. Lagerlund
58. DIGITAL SIGNAL PROCESSING: DIGITIZATION, AVERAGING, FILTERS, AND TIME/FREQUENCY DOMAIN ANALYSIS 1033
Terrence D. Lagerlund
59. ELECTRICAL SAFETY 1051
Terrence D. Lagerlund and Brian Nils Lundstrom
Index 1063
Preface
I took my seat in the classroom in the basement of the Guggenheim Building at Mayo Clinic, Rochester, Minnesota that first day of my clinical neurophysiology course during my PGY3 year of neurology residency, and was prepared to “put my time in” and “get through” the course so I could then focus on other areas of neurology that were of more interest to me at the time. As the course began and the passionate, brilliant, and dedicated faculty presented the intricacies and aspects of the various realms of clinical neurophysiology, I began to realize that clinical neurophysiology was not simply a required “foundation” class in neurology residency, but that clinical neurophysiology as a field is truly the foundation for ALL of neurology. I realized that, in essence, neurophysiology IS the nervous system, and all voluntary and involuntary functions in our bodies occur because of the physiologic changes in our neurons.
As the two months progressed, not only did I become more interested in neurophysiology as a field, but I came to realize the value of clinical neurophysiology testing in the diagnosis and understanding of patients’ symptoms. These methods of testing different portions of the nervous system have yielded important measures of identifying, studying, and following patients with diseases of the central and peripheral nervous system. While some of the methods of recording the electrical signals that are in current use today stem from early research and knowledge gained decades ago and are similar to those that I was taught in residency, there has been substantial and continued expansion and development of novel methods and techniques to further understand the nervous system. These advances continue to assist physicians and scientists to better recognize and treat neurologic diseases.
Clinical neurophysiology training at Mayo Clinic began over six decades ago. The lectures and handouts that were developed initially by Dr. Reginald Bickford in electroencephalography and Dr. Edward Lambert in electromyography were the seeds of what has grown into extensive, multidisciplinary training of clinicians in the various methods for assessing diseases of the central and peripheral nervous system. Through expansion of the focus on clinical neurophysiology education by other Mayo Clinic physicians, such as Drs. Donald Klass, Barbara Westmoreland, and Jasper Daube (who all taught me during my CNP course), education in clinical neurophysiology has grown in parallel with advances in techniques and knowledge in the field. Over time, the clinical neurophysiology educational programs at Mayo Clinic Rochester, Florida, and Arizona evolved into a formal, comprehensive 2-month course that provides trainees in multiple specialties (including neurology, physical medicine and rehabilitation, and neurosurgery) with the knowledge and experience needed to apply the principles of neurophysiology clinically. The course includes lectures, on-line digital educational programs, hands-on workshops and practice sessions, and clinical experience in each of the areas of clinical neurophysiology. Mayo Clinic staff neurophysiologists serve as faculty for the course; these faculty members are the authors of the chapters of this textbook. The material for the clinical neurophysiology course was initially consolidated from individual lecture handouts into manuals. The success of these manuals prompted the publication of the first edition of Clinical Neurophysiology in 1996 with subsequent editions in 2002, 2009, and 2016. The continued evolution and expansion of the field of clinical neurophysiology has resulted in this 5th edition. Clinical Neurophysiology, 5th edition is the result of the cumulative experience and advances in all areas of neurophysiology. While the content for the 5th edition of Clinical Neurophysiology expands upon previous editions and is based on Mayo Laboratory protocols, differences in the methods and techniques vary among institutions. Thus, the current edition also includes content based on established guidelines where applicable.
Clinical Neurophysiology, 5th edition approaches each of the major areas and types of tests individually. The first section is a review of the basics of clinical neurophysiology—knowledge that is common to each of the areas of clinical neurophysiology. The second section focuses on
clinical electroencephalography (EEG) and the associated studies to evaluate patients with epilepsy and central nervous system disorders. The third section focuses on the somatic peripheral neurophysiology and neuromuscular diseases and includes chapters on techniques and electrodiagnostic approaches to neuromuscular disorders. The fourth section is dedicated to evoked potential testing, which may be used to assess a variety of central and peripheral nervous system disorders. Subsequent sections focus on assessment of autonomic function, movement disorder neurophysiology, sleep disorders and polysomnography, and intraoperative monitoring. The final section reviews important foundation concepts, such as electricity and safety, common to all types of neurophysiologic testing.
Clinical Neurophysiology, 5th edition includes several new areas, such as chapters devoted to approach to patients with seizures and spells in the outpatient and inpatient setting, electrodiagnostic approaches to patients with different categories of neuromuscular disorders, pediatric sleep assessment and abnormal sleep disorders, and updated chapters on intraoperative monitoring.
The goal of this book is to provide the reader with a general, concise overview of the types of routine, advanced, and research testing used to evaluation the electrical properties of the nervous system. Through understanding the techniques and interpretations of these tests, the hope is that the reader will be able to apply the concepts into clinical practice and use this book as a resource in the evaluation of patients with a variety of central and peripheral nervous system diseases.
Acknowledgments
I would like to acknowledge and express my gratitude to all the authors of Clinical Neurophysiology, 5th edition, each of whom is active in clinical neurophysiology practice, education, and research. They bring their experiences and knowledge to bear in the chapters they have written. The neurophysiology faculty has also contributed in a large way to the clinical neurophysiology courses on which this textbook is based. As with previous editions, through reviewing the chapters in the editing process, my own knowledge and understanding in multiple areas of clinical neurophysiology has expanded, particularly those outside of my primary area of expertise.
Mayo Clinic Neurology leadership has continued to encourage and support the Clinical Neurophysiology faculty in their combined efforts to provide internal trainees as well as physicians around the world with the broad background of knowledge they will need as they enter and continue through active practice. This support has been critical in the continuation of the clinical neurophysiology course as well as allowed the faculty to develop new directions and unique training programs in clinical neurophysiology.
I would also acknowledge the trainees who have participated in our clinical neurophysiology program, our technologists who have played a major part in our teaching program, and the physicians who have participated in our continuing professional development courses. The feedback that we have received on our teaching material and the thoughtful questions that have been posed related to neurophysiology concepts and applications have allowed us to make continuous improvements and research within the field which, ultimately, helps to advance our understanding of the nervous system.
I would like to thank Kenna Atherton and William Hoffman of the Mayo Clinic Section of Scientific Publications, whose skill and professionalism have helped to ensure appropriate recognition of the figures used in many of the chapters.
Finally, I would like to acknowledge the late Dr. Jasper Daube, who was instrumental in teaching clinical neurophysiology not only to the authors of this book but to thousands of other residents, fellows, practitioners, and academicians over the decades. The concept of Clinical Neurophysiology began with Jasper, who was the original and sole editor of the first and second editions. Through his vision, clinical neurophysiology advanced as a subspecialty and he vastly broadened the knowledge and training in the field. He was an invaluable teacher, mentor, and friend to me. His vast experience, innovative ideas, and unparalleled dedication not only led to the advancement of the field of clinical neurophysiology, but also led to the training of countless numbers of physicians in clinical neurophysiology. Jasper’s legacy will remain a strong part of neurophysiology in the future, and he will always be an inspiration to me as I strive to improve the knowledge of as many students and physicians as possible, which will, in turn, improve the care of patients throughout the world.
Devon I. Rubin, MD
Contributors
Andrea J. Boon, MBChB
Professor of Neurology and Physical Medicine and Rehabilitation Mayo Clinic Rochester, MN, USA
James H. Bower, MD, MSc Professor of Neurology Mayo Clinic Rochester, MN, USA
Benjamin H. Brinkmann, PhD
Associate Professor of Neurology and Assistant Professor of Biomedical Engineering Mayo Clinic Rochester, MN, USA
Jeffrey W. Britton, MD Professor of Neurology Mayo Clinic Rochester, MN, USA
David B. Burkholder, MD Assistant Professor of Neurology Mayo Clinic Rochester, MN, USA
Jonathan L. Carter, MD
Associate Professor of Neurology Mayo Clinic Arizona Scottsdale, AZ, USA
John N. Caviness, MD Professor of Neurology Mayo Clinic Scottsdale, AZ, USA
William P. Cheshire Jr., MD Professor of Neurology Mayo Clinic Jacksonville, FL, USA
Elizabeth A. Coon, MD
Assistant Professor of Neurology Mayo Clinic Rochester, MN, USA
Amy Z. Crepeau, MD
Assistant Professor of Neurology Mayo Clinic Phoenix, Arizona, USA
Brian A. Crum, MD
Associate Professor of Neurology Mayo Clinic Rochester, MN, USA
Jasper R. Daube, MD Professor of Neurology Mayo Clinic Rochester, MN, USA
Elliot L. Dimberg, MD
Assistant Professor of Neurology Mayo Clinic Jacksonville, FL, USA
Joseph F. Drazkowski, MD Professor of Neurology Mayo Clinic Phoenix, AZ, USA
Robert D. Fealey, MD
Assistant Professor of Neurology (Emeritus) Mayo Clinic Rochester, MN, USA
Anteneh M. Feyissa, MD, MSc Associate Professor of Neurology Mayo Clinic Jacksonville, FL, USA
Brent P. Goodman, MD
Assistant Professor of Neurology Mayo Clinic Scottsdale, AZ, USA
Cameron D. Harris, BS, RPSGT
Assistant Professor of Medicine (Retired) Mayo Clinic Rochester, MN, USA
Anhar Hassan, MBBCh, FRACP
Associate Professor of Neurology Mayo Clinic
Rochester, MN, USA
E. Matthew Hoffman, DO, PhD
Assistant Professor of Neurology Mayo Clinic
Rochester, MN, USA
Lyell K. Jones Jr., MD Professor of Neurology Mayo Clinic Rochester, MN, USA
Mithra R. Junna
Assistant Professor of Neurology Mayo Clinic
Rochester, MN, USA
Kathleen D. Kennelly, MD, PhD
Assistant Professor of Neurology Mayo Clinic
Jacksonville, FL, USA
Julie A. Khoury, MD
Assistant Professor of Neurology Mayo Clinic
Scottsdale, AZ, USA
Bryan T. Klassen, MD
Assistant Professor of Neurology
Mayo Clinic
Rochester, MN, USA
Suresh Kotagal, MD Professor of Neurology Mayo Clinic
Division of Child Neurology Rochester, Minnesota, USA
Terrence D. Lagerlund, MD, PhD
Associate Professor of Neurology Mayo Clinic
Rochester, MN, USA
Ruple S. Laughlin, MD
Associate Professor of Neurology Mayo Clinic
Rochester, MN, USA
Teerin Liewluck, MD
Associate Professor of Neurology Mayo Clinic
Rochester, MN, USA
Phillip A. Low, MD Professor of Neurology Mayo Clinic
Rochester, MN, USA
Brian Nils Lundstrom, MD, PhD
Assistant Professor of Biophysics and Neurology
Mayo Clinic
Rochester, MN, USA
Michelle L. Mauermann, MD Professor of Neurology Mayo Clinic
Rochester, MN, USA
Elizabeth A. Mauricio, MD
Assistant Professor of Neurology Mayo Clinic Jacksonville, FL, USA
C. Michel Harper Jr., MD Professor of Neurology Mayo Clinic Rochester, MN, USA
Iryna M. Muzyka, MD
Assistant Professor of Neurology Mayo Clinic
Scottsdale, AZ, USA
Elie Naddaf, MD
Assistant Professor of Neurology Mayo Clinic
Rochester, MN, USA
Katherine C. Nickels, MD
Associate Professor of Neurology Mayo Clinic
Rochester, MN, USA
Katherine H. Noe, MD, PhD
Associate Professor of Neurology Mayo Clinic Phoenix, AZ, USA
Devon I. Rubin, MD
Professor of Neurology Mayo Clinic
Jacksonville, Florida, USA
Jaimin S. Shah, MD Instructor in Neurology Mayo Clinic Jacksonville, FL, USA
Cheolsu Shin, MD
Associate Professor of Neurology (Emeritus)
Mayo Clinic
Rochester, MN, USA
Michael H. Silber, MBChB Professor of Neurology Mayo Clinic Rochester, MN, USA
Wolfgang Singer, MD Associate Professor of Neurology Mayo Clinic Rochester, MN, USA
Joseph I. Sirven, MD Professor of Neurology Mayo Clinic Jacksonville, Florida, USA
Benn E. Smith, MD
Associate Professor of Neurology Mayo Clinic
Scottsdale, AZ, USA
Elson L. So, MD Professor of Neurology Mayo Clinic Rochester, MN, USA
Eric J. Sorenson, MD Professor of Neurology Mayo Clinic Rochester, MN, USA
Erik K. St. Louis, MD, MS Associate Professor of Neurology Mayo Clinic Rochester, MN, USA
Nathan P. Staff, MD., PhD Professor of Neurology Mayo Clinic Rochester, MN, USA
Jeffrey A. Strommen, MD
Associate Professor of Physical Medicine and Rehabilitation
Mayo Clinic Rochester, MN, USA
William O. Tatum, DO Professor of Neurology Mayo Clinic Jacksonville, Florida, USA
Rene L. Utianski, PhD, CCC-SLP Associate Professor of Speech Pathology
Assistant Professor of Neurology Mayo Clinic Rochester, MN, USA
James C. Watson, MD Professor of Neurology and Anesthesiology
Mayo Clinic Rochester, MN, USA
Elaine C. Wirrell, BSc (Hon), MD Professor of Neurology Mayo Clinic Rochester, MN, USA
Lily C. Wong-Kisiel, MD
Associate Professor of Neurology Mayo Clinic Rochester, MN, USA
Gregory A. Worrell, MD, PhD Professor of Neurology Physiology and Biomedical Engineering Mayo Clinic Rochester, MN, USA
Introduction
SECTION I—BASIC NEUROPHYSIOLOGY
Our nervous system controls every function in our bodies. The neurons at every level of the nervous system—cortex, brainstem, spinal cord, cranial and peripheral nerves, neuromuscular junctions, and muscles—are ultimately involved in every type of voluntary and involuntary activity that occurs within our bodies to allow us to function as human beings. Without our nervous systems, we cannot function appropriately or even survive. In conditions resulting in a focal loss of neurons, one may experience symptoms localized to one part of the body, such as paralysis, involuntary shaking, or loss of feeling in an arm or a leg; in other situations, abnormally functioning neurons in a more diffuse distribution may result in generalized symptoms, such as a loss of consciousness or diffuse weakness. The electrical properties of the neurons and their communications with each other and other organs help to maintain the multitude of functions that allow us to exist. Clinical neurophysiology is the study of the electrical properties of these cells. If these electrical signals “go awry,” resulting in either an increase in excitation or loss of excitability, neurologic symptoms develop. For example,
hyperexcitability of cortical or subcortical neurons may result in seizures or movement disorders, whereas loss of function of central or peripheral neurons may result in paralysis, orthostatic hypotension, or peripheral neuropathy.
In clinical neurophysiology, neural function is assessed by measuring the electric potentials generated by neural tissue and the changes in these potentials produced by disease. These potentials can be studied in every system—consciousness, motor, sensory, autonomic, and movement. They can be studied in awake or asleep patients in the outpatient setting, in patients in a state of unconsciousness in the intensive care unit (ICU), or in patients undergoing surgery in the operative setting. The various tests used to assess nerve function have been routinely used in clinical practice for decades. While the basics of the tests and the underlying concepts of basic neurophysiology have not dramatically changed in the past several years, advances in the ability to study the intricacies of the systems, technologic improvements in equipment, and advances in the methods to detect subtle changes in the nerve function continue. The fifth edition of Clinical Neurophysiology focuses on neurophysiologic techniques and applications that are used in clinical practice to assist physicians
in the evaluation of a variety of neurologic symptoms and diseases.
An understanding of the basic concepts of neurophysiology is critical to understanding the meaning and implications of each type of test performed in clinical practice. Furthermore, understanding the generator sites and waveforms produced from the electrical signals is important, as they form the basis of interpretation of the studies. The book begins with three chapters that review of the concepts of basic neurophysiology (Chapter 1), neurophysiology generators (Chapter 2), and basic waveforms (chapter 3); these chapters provide an important foundation for understanding the rationale and responses obtained with the different types of testing detailed in subsequent sections.
SECTION II—CLINICAL ELECTROENCEPHALOGRAPHY
Clinical electroencephalography (EEG) records the continuous electrical signals arising from cerebral cortex using electrodes applied to the scalp. The patterns of the signals can provide important clues to the underlying function of the cortex and the presence of diseases that affect the brain. The techniques of EEG are used primarily to assess disorders that affect the cerebral cortex, including seizures, spells, and disorders of consciousness, and are used to monitor the function of the cerebral cortex during surgeries that place the cortex at risk of injury. The EEG techniques and patterns detailed in Chapters 4–9 reflect the normal and abnormal EEG findings and the alterations in disease processes that directly involve the cerebral cortex in the adult and pediatric populations.
Expansion of EEG beyond that performed in the outpatient EEG laboratory setting has proven necessary in order to more effectively study epilepsy and related conditions. For example, longer recordings may be needed to document infrequent episodes or sporadic interictal activity and to provide clinical correlation. Long-term, computer-assisted ambulatory EEG recordings can be used to provide a longer duration EEG recording in a patient’s home environment in cases where symptoms are suspicious for seizures yet the routine EEG
is negative (Chapter 10). In patients who are unable to utilize ambulatory EEG or those in whom more in-depth assessment of epilepsy to identify a precise seizure focus often require prolonged video-EEG monitoring in an inpatient setting. Video-EEG monitoring in an epilepsy monitoring unit (EMU) allows correlation of a patient’s clinical activity as viewable on video with the EEG, which helps in determining whether a patient’s clinical events are seizures, syncope, or due to other causes (Chapter 11). Long-term EEG analysis is also being increasingly utilized in patients in the ICU to established trends that indicate cerebral function or seizures. The EEG is an important tool in the ICU setting for the diagnosis and management of status epilepticus. It is also useful in this setting for the purposes of monitoring cerebral activity in certain neurologic critical care disorders, such as for the detection of vasospasm in subarachnoid hemorrhage, changes in function in traumatic brain injury and stroke, and the detection of nonconvulsive seizure activity that may impact neurologic function (Chapter 12). Finally, patients being considered for epilepsy surgery require highly specialized recordings, utilizing intracranial electrodes and advanced methods of analysis, including new correlations with magnetic resonance imaging (Chapter 13 and 14). While each of these techniques is discussed in detail in their respective chapters in this section, Chapters 15 and 16 provide a practical overview of the clinical applications of neurophysiologic testing when assessing patients with spells or seizures in the outpatient setting and during evaluation for epilepsy surgery.
SECTION III—CLINICAL ELECTROMYOGRAPHY
Neuromuscular diseases manifest with variable symptoms, signs, distributions of deficits, and degrees of severity. They may involve any level of the peripheral nervous system, from the anterior horn cell to the muscle and may involve the bulbar, upper, or lower extremity regions. Some disorders may be focal, such as an ulnar mononeuropathy, and others diffuse, such as motor neuron disease; some are symmetric and others asymmetric.
In some cases, patient’s symptoms are so characteristic of a specific neuromuscular disorder that additional testing may not be warranted to confirm the diagnosis; however, in many instances the symptoms or signs may suggest several possible diagnoses. Clinical electromyography (EMG) methods test the peripheral nervous system, provide objective evidence of the function of the neuromuscular system, and help confirm a suspected clinical diagnosis.
Several types of studies may be used to evaluate neuromuscular diseases. This section of Clinical Neurophysiology, 5th edition , reviews the different types of tests used in the neuromuscular electrodiagnostic examination. Motor conduction studies and sensory nerve conduction studies (NCSs) (Chapters 17 and 18) assess the function of the peripheral axons, and motor NCSs also provide information regarding the neuromuscular junction and muscle. Since these routine studies mostly assess the distal nerve segments, late responses such as the F wave and H reflexes may be incorporated to assess proximal nerve segments (Chapter 19). Repetitive nerve stimulation is an advanced technique used to assess patients with suspected disorders of neuromuscular transmission, such as myasthenia gravis or Lambert- Eaton syndrome (Chapter 20). Less commonly, patients are referred for primarily symptoms involving cranial nerves or muscles, and unique neurophysiologic cranial reflexes can be assessed in the EMG laboratory (Chapter 21). Although less commonly used for diagnostic purposes, motor unit number estimates are techniques that can provide an objective estimate of the number of motor units in a muscle and can be used to follow the progression of patients with neuromuscular diseases, such as amyotrophic lateral sclerosis (Chapter 22). Each of these types of conduction studies may be fraught with potential technical pitfalls that may impede reliable interpretation of the results. The pitfalls and potential complications of NCSs are reviewed in Chapter 23.
The electrophysiologic assessments described in the needle EMG section complement NCSs in defining the character, severity, and distribution of neuromuscular diseases. Distinguishing among primary muscle
diseases, disorders of the neuromuscular junction, and neurogenic disorders usually depends on the findings on needle EMG (Chapter 24) since many of these may demonstrate similar or no findings on NCSs. In addition, needle EMG helps characterize the number of functioning axons or anterior horn cells, the size of the motor units, and defects of neuromuscular transmission. These aspects of neuromuscular disease can be quantified more precisely with the special techniques of quantitative EMG (Chapter 25) and single-fiber EMG (Chapter 26). Needle EMG has potential risks and pitfalls that can affect interpretation of the recording, and these are discussed in Chapter 27. Chapters 28–35 review the clinical applications, approaches, and findings of these tests in mononeuropathies, radiculopathies, plexopathies, polyneuropathies, motor neuron diseases, neuromuscular junction diseases, myopathies, and neuromuscular disorders encountered in the ICU. Finally, neuromuscular ultrasound is now commonly incorporated in EMG laboratories as a complement to NCSs and needle EMG; the utility of ultrasound is reviewed in Chapter 36.
SECTION IV—EVOKED POTENTIALS
While NCSs are considered one type of evoked potential technique, they only assess the peripheral nervous system. In clinical practice, testing regions of the central nervous system may be important to identify and follow disease. In this section, testing of other evoked potentials, primarily of the central nervous system, are detailed. The somatosensory pathways, from the distal sensory nerve to the somatosensory cortex, can be tested with somatosensory evoked potentials (Chapter 37), the visual pathway with visual evoked potentials (Chapter 38), the peripheral and central auditory pathway with brainstem auditory evoked responses (Chapter 39), and the motor system with motor evoked potentials (Chapter 40). Each of these techniques may be used in a variety of clinical situations, such as in the evaluation for central demyelination diseases (e.g., multiple sclerosis), myelopathies, or diseases affecting the optic nerves or the brainstem.
SECTION V—ASSESSMENT OF AUTONOMIC FUNCTION
The autonomic nervous system controls many of our “automatic” functions, including heart rate and blood pressure, sweating, urogenital functions, and gastric motility. It regulates visceral function and the internal environment of the body through its effects on the heart, intestine and other internal organs, peripheral blood vessels, and sweat glands (Chapter 41). Autonomic dysfunction is often underrecognized in neurologic diseases. Clinical signs of autonomic dysfunction are easily overlooked, and neural activity in the autonomic nervous system is difficult to record directly. Involvement of the autonomic nervous system may occur in various neurological diseases involving the central nervous system (e.g., multiple system atrophy) or peripheral nervous system (e.g., diabetic polyneuropathy). Assessment of autonomic function depends primarily on measuring the response of the autonomic nervous system to external stimuli, which can be accomplished with several neurophysiological tests.
The measurements of sweating (Chapters 42 and 44), cardiovascular activity and peripheral blood flow (Chapters 43 and 45), and central autonomic-mediated reflexes provide insight into the broad range of disorders that affect the central and peripheral components of the autonomic nervous system—from the hypothalamus to the autonomic axons in the trunk and limbs. With better understanding of the clinical importance of measuring autonomic function and with increasing use of tests of cardiovagal function, segmental sympathetic reflexes, postural hemodynamics, and power spectral analysis, the tests and measurements of autonomic function will continue to be of benefit in patient care.
SECTION VI—CLINICAL NEUROPHYSIOLOGY OF MOVEMENT DISORDERS
The evaluation of patients with movement disorders primarily relies on the clinical neurological examination findings to help characterize the abnormal movements. However,
sometimes the clinical features may be difficult to classify, such as for a tremulous patient, who may have a fine tremor or orthostatic myoclonus. Neurophysiologic techniques can be useful and complementary to the neurologic examination in classifying abnormal movements. Movement-related and event-related potentials utilize specialized EEG recordings that are time locked to specific movements to help characterize the generator of the movements (Chapter 46). Techniques such as long latency reflexes (Chapter 47) or surface EMG (Chapter 48) may be used in the assessment of patients with tremor, myoclonus, dystonia, or other movement disorders
SECTION VII—ASSESSMENT OF SLEEP
The subspecialty of sleep medicine includes various medical specialists—neurologists, pulmonologists, and psychiatrists. Neurophysiologic techniques of polysomnography are important in the evaluation of a patient with a suspected sleep disorder. Multiple physiologic parameters can be assessed using one or a combination of polysomnography, multiple sleep latency or maintenance of wakefulness tests, actigraphy, and portable monitoring. Chapter 49 reviews the techniques that are available to study sleep and disorders that may occur during sleep, and Chapter 50 discusses application of these tests to the pediatric population. The use of these tests is helpful not only to identify different stages of sleep, but also to assess sleep disorders, such as sleep apnea, other disorders manifesting with excessive somnolence, and parasomnias (Chapter 51).
SECTION VIII—INTRAOPERATIVE MONITORING
Neurophysiologic monitoring has become the standard of care during many operative procedures involving the spine, brainstem, cranial nerves, and cortex. Monitoring the electrical signals during surgical procedures that may place critical nervous system structures at risk can help to alert the surgeon to potential injury. Many of the neurophysiologic testing
modalities used in the outpatient setting can be incorporated, with some modifications, in the operating room. Cerebral monitoring with EEG and somatosensory and motor evoked potentials may be used during epilepsy surgery or cranial surgery to help identify specific structures within the cortex (Chapter 52). Monitoring of brainstem function and cranial nerve function during posterior fossa surgeries, such as microvascular decompression for trigeminal neuralgia or posterior fossa tumor resections, can be performed using brainstem auditory and somatosensory evoked potentials, nerve action potentials, and EMG (Chapter 53). Intraoperative monitoring of spine surgeries is the most common use of neurophysiologic monitoring in the operating room and typically combines somatosensory evoked potentials, motor evoked potentials, and EMG to monitor the function of the spinal cord and nerve roots (Chapter 54). Finally, peripheral nerve monitoring may be utilized in brachial plexus
reconstruction surgeries or surgeries involving individual nerves or roots (Chapter 55).
SECTION IX—ELECTRICAL CONCEPTS AND SAFETY
Concepts that are inherent to all of the electrical activity in the nervsous system and relate to the safe performance and interpretation of neurophysiolologic studies are reviewed in section IX. Volume conduction (Chapter 56) relates to the ability to record generated signals from a structure from nearby or distant recording electrodes. Various components of the electrical equipment and their effect on the recorded responses are reviewed in Chapter 57. The process and effect of digital signal processing is discussed in Chapter 58. Finally, important electrical safety issues that are critical to the performance of safe studies are reviewed in Chapter 59.
