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Despite several antibody tests being available for the assessment of disorders of neuromuscular transmission, electrophysiological testing of the neuromuscular junction remains a very important part of clinical practice. The neuromuscular junction is a complex structure and an understanding of its anatomy and physiology can assist in better understanding the value of electrodiagnostic testing. The most common disorders include myasthenia gravis, Lambert-Eaton myasthenic syndrome, and botulism, and are usually readily identified using several electrophysiological techniques including slow (2-3 Hz) and fast (20- to 50-Hz stimulation). Single-fiber needle EMG remains an additional powerful and sensitive test for patients with disorders that are more mild, in whom repetitive stimulation testing is negative or indeterminate.

A variety of neuromuscular conditions affect children, ranging from severe, usually fatal disorders, such as spinal muscular atrophy type I (Werdnig-Hoffman syndrome) to relatively mild problems, such as benign congenital hypotonia. The evaluation of children in the EMG laboratory requires special care because of the discomfort of the tests. Moreover, other considerations, such as slower baseline nerve conduction velocities and conditions that generally do not present in adulthood, such as congenital myasthenic syndromes, can make the pediatric neurophysiological examination especially challenging. This chapter reviews both the common pediatric neuromuscular conditions and their assessment in the EMG laboratory.

The classification of sleep disorders is based both on clinical and neurophysiological criteria and is undergoing constant refinement. Sleep disorders can be caused by either a primary disorder of a mechanism controlling sleep or inadequate function of an end organ, such as the upper airways and lungs. Understanding the physiology and pattern of normal sleep is an important foundation for interpreting the clinical symptoms, signs, and neurophysiological abnormalities observed in patients with sleep disorders. The term polysomnography refers to the simultaneous recording of multiple sleep parameters, including a limited electroencephalogram, respiratory parameters, chest excursion, limb movements, and the electrocardiogram. Polysomnography is important for assessing a variety of sleep disturbances, including disorders such as sleep-related breathing disorders (including obstructive sleep apnea), rapid eye movement behavior disorder, and periodic movements of sleep. The multiple sleep latency test and maintenance of wakefulness test are studies that are especially useful in the evaluation of narcolepsy and other hypersomnias.

Autonomic testing encompasses an array of procedures that can be used to assess a variety of symptoms ranging from lightheadedness and dizziness to anhydrosis to constipation and urinary incontinence. A number of procedures are available for testing of the many varied aspects of both the parasympafhetic and sympathetic nervous systems. These tests include Valsalva maneuver testing, RR interval testing, tilt-table testing, microneurography, and the thermoregulatory sweat test. This chapter reviews the basic neuroanatomy and neurophysiology of the autonomie nervous system and the tests that are most effective in their evaluation.

The visual evoked potential (VEP) is primarily a relatively large, positive polarity wave generated in the occipital cortex in response to visual stimulation. It measures the conduction time of neuronal activity from the retina to the occipital cortex and is used clinically as a measure of the integrity and function of that pathway. The optic nerve is the primary structure examined. The standard VEP averages many responses, time-locked to a photic stimulus. Of primary interest is the latency of the positive wave at a midline occipital EEG electrode, usually at approx 100 ms after stimulation, called the P100. This chapter summarizes the methodology for recording the VEP, provides an approach to its interpretation, and discusses its role in clinical practice.

Brainstem auditory evoked potentials (BAEPs) are electrical field potentials generated by stimulation of the auditory pathways. With repetitive auditory stimulation, reproducible electrical potentials can be elicited and recorded from scalp electrodes. These waves are generated by specific brain regions and occur at predictable intervals. Clinically, this neurophysiological property is useful to evaluate the integrity of auditory pathways (plus, by extension, neighboring CNS structures) and to localize defective transmission. This chapter summarizes the methodology and clinical application of BAEPs in the investigation of disorders affecting auditory pathways and the surrounding brainstem.

Somatosensory evoked potentials (SSEPs) are electrical potentials generated by various portions of the ascending sensory pathways in response to stimulation of peripheral sensory nerves. SSEPs can be easily elicited and recorded and can be used to examine the functional integrity of somatosensory pathways. This chapter summarizes the methodology for the recording of SSEPs, as well as their role in the evaluation of processes that may affect ascending sensory pathways (e.g., demyelination), and highlights their particular usefulness as an intraoperative tool during spinal cord surgery.

During the past two decades, transcranial magnetic stimulation (TMS) has emerged as an important modality for the exploration of cerebral function and assessing the integrity of human motor pathways. In TMS, a strong magnetic pulse activates neural elements oriented predominantly horizontally to the brain surface, and a motor evoked potential can be recorded in the activated muscles. In single-pulse TMS, stimulation can be applied to different levels of the nervous system, including the spinal cord, to assist in localizing a lesion to a specific level and helping to characterize it as demyelinating or axonal in nature. A central motor conduction time can also be calculated; this is defined as the latency difference between the motor evoked potentials induced by stimulation of the motor cortex and those evoked by spinal (motor root) stimulation. A variety of additional testing paradigms have been created over the years, including the use of paired-pulse techniques and repetitive stimulation, the latter potentially assisting in treating a variety of disorders, including depression and Parkinson disease.