Chapter 17: Electrophysiological Testing of Nerves and Muscles

WHAT IS ELECTRONEUROMYOGRAPHY?

Clinical electroneuromyography (ENMG) includes observing, analyzing, and interpreting the bioelectrical activity of muscles and nerves as they respond to electrical stimulation, needle provocation, and voluntary activation. Most often, the testing consists of a combination of nerve conduction studies (NCSs) and electromyography (EMG), although additional tests may occasionally be appropriate. These may include somato-sensory-evoked potentials, brainstem auditory-evoked potentials, visual-evoked potentials, intraoperative monitoring, and repetitive stimulation. Of these additional electrophysiological tests, somatosensory-evoked potentials and repetitive stimulation are more commonly accomplished on a routine basis. However, this overview focuses on clinical NCS and EMG studies.

EMG and NCS have been a part of physical therapy practice for well over 50 years and are documented in the original and subsequent versions of the Guide to Physical Therapist Practice.¹ In the 1980s, the APTA was determined to encourage specialization within the broad profession of physical therapy and one such area of specialization was Clinical Electrophysiology (primarily EMG and NCS). Specialization in this area

acknowledged that electrophysiologic testing was a germane aspect of the practice of physical therapy and represented an example of the expansion of the knowledge base required of physical therapists and was one of many reasons that we have seen the practice of physical therapy develop into a “doctoring profession.” An important aspect of the doctoring physical therapy profession is the responsibility to determine, as Delitto² and others have proposed, whether a patient can be appropriately treated by the physical therapist without assistance or additional information, or a patient for whom our treatment should proceed with additional information provided by other medical specialists or special test data (imaging, blood studies, EMG/NCS, etc.). For this reason, physical therapists are required to be acquainted with the information provided by such testing and this serves as a primary reason many professional physical therapy programs include didactic and practical experiences on EMG/NCS in their curriculum.

ANATOMY AND PHYSIOLOGY REVIEW

Peripheral Nerve Structure

The anatomic unit of the nervous system is the neuron, with its various processes or nerve fibers.³ By contrast, the functional unit of the neuromuscular system is the motor unit, consisting of the anterior horn cell, the nerve root, the plexus, individual nerve fibers, the neuromuscular junction (NMJ), and all the muscle fibers innervated by that axon (Fig. 17-1).

ENMG testing assesses various aspects of the neuron and the motor unit. EMG testing examines the delineated components of the motor unit, allowing the practitioner to determine the location of a ...