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Clinical Neurophysiology CHAPTER 12 Committee 8 Clinical Neurophysiology Chairman D.B. VODUSEK (SLOVENIA), Members G. AMARENCO (FRANCE), A. BATRA (USA), T. BENSON (USA), A.E. BHARUCHA (USA), S. PODNAR (SLOVENIA), C.C. YANG (USA) Consultant B. SCHURCH (SWITZERLAND) Disclaimer: The views and opinions expressed in the chapter are those of the authors and do not represent the views or the policies of the US Food and Drug Administration. 675 CONTENTS INTRODUCTION II. USEFULNESS OF CLINICAL NEUROPHYSIOLOGICAL TESTS IN EVALUATION OF INDIVIDUAL A. GENERAL PATIENTS WITH LOWER URINARY CONSIDERATIONS TRACT OR ANORECTAL DYSFUNCTION I. HISTORICAL BACKGROUND III. USEFULNESS OF CLINICAL NEUROPHYSIOLOGICAL TESTS IN II. CLASSIFICATION OF CLINICAL RESEARCH NEUROPHYSIOLOGICAL TESTS D. RECOMMENDATIONS III. GENERAL METHODOLOGICAL CONSIDERATIONS I. CLINICAL RECOMMENDATIONS B. CLINICAL NEUROPHYSIO- II. RECOMMENDATION FOR LOGICAL TESTS TECHNICAL STANDARDS III. RESEARCH I. SOMATIC MOTOR SYSTEM RECOMMENDATIONS TESTS E. APPENDIX II. SENSORY SYSTEM TESTS ANALYSIS OF THE CONCENTRIC III. SACRAL REFLEXES NEEDLE EMG SIGNAL IV. AUTONOMIC NERVOUS SYSTEM REFERENCES TESTS ABBREVIATIONS USED MSA – multiple system atrophy IN TEXT MU – motor unit C. GENERAL COMMENTS ON MUP – motor unit potential BCR – bulbocavernosus reflex PD – Parkinson's disease NEUROPHYSIOLOGICAL CMAP – compound muscle PNTML – pudendal nerve ter- action potential minal motor latency TESTING CMCT – central motor QST – quantitative sensory conduction time testing CNEMG – concentric needle SEP – somatosensory evoked I. EVIDENCE BASED USE, electromyography potential CRITERIA FOR ABNORMALITY, EAS – external anal sphincter SFEMG – single fibre electro- ED – erectile dysfunction myography SENSITIVITY AND SPECIFICITY OF EMG – electromyography SSR – sympathetic skin CLINICAL NEUROPHYSIOLOGICAL GSI – genuine stress responses incontinence SUI – stress urinary TESTS IP – interference pattern incontinence MEP – motor evoked potential T/A – turns / amplitude 676 Clinical Neurophysiology D.B. VODUSEK, G. AMARENCO, A. BATRA, T. BENSON, A.E. BHARUCHA, S. PODNAR, C.C. YANG was first performed by Danish investigators [3] wor- INTRODUCTION king with the founder of electromyography Buch- thal. This was followed by the use of kinesiological Neurophysiological investigations of the bladder and EMG recordings during urodynamics. [4] Latency anorectum originated over 60 years ago, and have recordings of the bulbocavernosus reflex were repor- evolved with the developments in general clinical ted [5] soon after electrical stimulation for motor neurophysiology. The data from these investigations conduction studies had been introduced. Recording can assist clinicians in diagnosing neurological of evoked potentials following repetitive stimulation disease or injury of the uro-genital-anal organs. Ano- of the pudendal nerves [6] and other pelvic sensory ther application of neurophysiological testing is in nerves developed within a few years of the introduc- research, to identify the neural pathways that media- tion of somatosensory evoked potential recordings te urogenital and anorectal function. Compared to into general clinical practice. Cortical and nerve root neurophysiological testing of the limbs and trunk, stimulation by first electrical [7] and then magnetic pelvic neurophysiological testing is relatively limi- stimulation[8] while recording from pelvic floor ted, primarily because of the restrictions imposed by musculature followed afterwards. pelvic neuroanatomy. This chapter details the investigations, their applica- II. CLASSIFICATION OF CLINICAL tions and limitations, enabling investigators and cli- NEUROPHYSIOLOGICAL TESTS nicians to make a well informed decision about using these tests. It is possible to classify neurophysiological tests in The present text is based on the two previous chap- different ways. As the tests are an extension of the ters on clinical neurophysiology prepared for the clinical examination, a functional anatomic approach International Consultations on Incontinence.[1, 2] to classification makes most sense. For the purpose of this categorisation, the nervous system is divided into the somatic and the autonomic nervous systems. A. GENERAL The somatic nervous system provides motor innerva- CONSIDERATIONS tion to the skeletal muscles and joints, and sensory innervation from skin and muscle spindles. The auto- nomic nervous system provides motor innervation to the viscera and other endorgans not under voluntary I. HISTORICAL BACKGROUND control (e.g., sweat glands). Its sensory fibers are referred to as visceral afferents. Both systems have central pathways (neurons participating in spinal Neurophysiological techniques to investigate pelvic cord and supraspinal control) and peripheral nerves organ and pelvic floor function evolved as general (those going to and from endorgans). clinical neurophysiological techniques developed and were applied to these structures. Sphincter EMG We have applied this simplified classification to the 677 innervation of the pelvis, generally classifying the nerve action potential [9]. Supramaximal stimuli electrophysiological tests as tests of the a) the soma- yield responses with the largest amplitude and shor- tic motor system (EMG, terminal motor latency mea- test latency, and are the least variable and most surements/ motor nerve conduction studies, and reproducible. The sites at which stimulation elec- motor evoked potentials (MEP)); b) the somatosen- trodes are applied should be described using anato- sory system (sensory neurography, somatosensory mical terms. evoked potentials (SEP)); c) reflexes, which assess whole reflex arcs including sensory and motor 3. RECORDING PARAMETERS nerves; and d) the autonomic nervous system (i.e., assessing the function of sympathetic or parasympa- a) Apparatus settings thetic fibres). For recording, the apparatus settings (gain, sweep speed) have to be adapted to the known range of amplitudes, latencies, and duration of the response III. GENERAL METHODOLOGICAL and it has to be appropriately displayed for analysis. CONSIDERATIONS Particularly important is the frequency setting of fil- ters: for surface electrode recordings it is typically 2 Hz – 1000 Hz; for needle EMG recordings, it is 5 – 1. EQUIPMENT 10000 Hz for concentric needle or 500 – 10000 Hz Clinical neurophysiological tests are conducted with for single fibre needle. complex electronic instruments and various devices Placement of electrodes on the scalp for evoked that come into contact with the patient. Though this potential recordings is defined according to the 10- equipment is mostly standard, some specially 20 International EEG System. constructed electrodes or stimulating devices have been devised to conform to uro-genito-anal anatomy. b) Reproducibility and Reliablity As long as the standards of electrical safety are adhe- Any potential elicited by stimulation should be red to, the risk to patients is negligible. reproducible; therefore, as a rule, at least two conse- The most common form of neurophysiological tes- cutive recording procedures need to be performed. ting is electrophysiological, whereby neurons are Some responses need to be averaged because of their depolarized with electrical current. Surface elec- small amplitude to improve the signal-to-noise ratio. trodes, which are applied to skin or mucosal sur- Therefore, many repetitions of stimulation/recording faces, or needle electrodes are used for electrical sti- need to be done (typically 100-200). Even such an mulation and to record bioelectrical activity. The averaged recording needs to be repeated at least important neurophysiological difference between twice. CMAPs or M waves, MEP, sacral reflexes and surface and needle electrodes is their selectivity, and sympathetic skin responses (SSR) are recognisable the practical difference is their invasiveness. The after single stimuli. However, as a rule, several res- choice and application of electrodes is guided by the ponses are recorded to demonstrate reproducibility. need for selective recording or stimulation. Less In contrast, other responses (e.g., sympathetic skin commonly, special devices are used for magnetic and responses) show marked fatigability with stimulus mechanical stimulation. To date, there are no gene- repetition. rally accepted guidelines for conducting individual uro-genital-anal neurophysiological tests. c) Waveform Analysis For a particular stimulation procedure, the shape, 2. STIMULATION PARAMETERS latency, and amplitude of the recorded potentials are The electrical stimulus should be specified and cha- analysed. Morphologically, a particular response (or racterised both in technical (e.g., rectangular pulse, part of it) needs to be recognised as present or absent. 0.2 ms, 15 mA) and physiological terms (e.g., 3- The shape of potentials is important to accurately times sensory threshold). A stimulus with defined determine the latency and amplitude of the response. technical parameters may have variable biological The onset of the response (for M waves, MEP and effects because of the variable influences of electro- sacral reflex testing) or the individual peaks of the de condition, contact, tissue conductivity etc. Supra- potentials (for SEP) are used to determine the laten- maximal stimulation is preferred to elicit a com- cy. The amplitudes are analysed relative to the base- pound muscle action potential (CMAP) or sensory line or “peak to peak”. 678 4. ANATOMIC CORRELATES OF NEUROPHYSIO- sympathetic skin responses, relate not only to LOGIC
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