Basic Principles in Nerve Conduction Studies

Lee, Dong Kuck

Ann Clin Neurophysiol > 2003 ;5(1) > Article

Ann Clin Neurophysiol. 2003; 5(1): 119-131.

Dong Kuck Lee

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Electrodiagnostic studies can be a valuable method in the diagnosis and follow-up study of various neuromuscular diseases. They must be used as an extension of the clinical evaluation, however, and not as routine tests. After the physician decides what kinds of pathophysiology could explain the patient? signs and symptoms, he or she is then in a position to request specific electromyography (EMG) studies to shed light on diseases that could affect the anterior horn cells, nerve roots, peripheral nerve, neuromuscular junctions, or muscles. Nerve conduction studies (NCS) assess peripheral motor and sensory functions by recording the evoked response to stimulation of peripheral nerves. Motor NCS require stimulation of a peripheral nerve while recording from a muscle innervated by that nerve. Sensory NCS are performed by stimulating a mixed nerve while recording from a cutaneous nerve or by stimulating a cutaneous nerve while recording from a mixed or cutaneous nerve. Motor and sensory NCS studies have been used clinically for many years to identify the location of peripheral nerve disease in single nerves and along the length of nerves and to differentiate these disorders from diseases of muscle or the neuromuscular junction. NCS also can help to distinguish between axonal degeneration, segmental demyelination, and abnormal nerve irritability. But it is important to recognize the inherent limitations of the EMG study. First, the kinds of tests and the muscles or nerves to be tested must be determined by clinical findings. Then, the EMG findings must be interpreted in light of the clinical findings because no EMG results are pathognomonic of a specific disease entity. For these reasons, it is essential that the clinical problem be assessed throughly and that a careful neurological examination be performed before the electrophysiologic study.

Key words: Electromyography, Nerve conduction studies