-Abstract-
The needle EMG study became a routine diagnostic work-up for various
neuromuscular disorders including myopathies, neuromuscular junction disease, motor
neuron diseases and other lower motor neuron disorders. The development of the
computerized modern EMG machines also enabled accurate and detailed analysis of the
motor unit physiology available in most of the electrophysiology laboratory. The main
purpose of this article is to illustrate the technique and interpretation of the needle EMG
finding. In the first part of the article, the basic anatomy and physiology of the motor
unit, technique of the needle EMG examination and motor unit potential(MUP) analysis
is reviewed. A MUP, which can be identified with conventional needle EMG study, is
composed of action potentials of individual muscle fibers belonging to the same motor
unit, and thus, its morphological changes reflect physiological and pathological alterations
of the motor unit. In the second part of the article, single fiber electromyography
(SFEMG) technique is briefly reviewed. As the action potentials of individual muscle
fibers cannot be recorded with the conventional needle EMG technique, this technique
requires specialized needle electrode and higher filter setting for the selective recording
of the single fiber action potential(SFAP), and lower sweep velocity for the better
separation of different SFAPs. Although SFEMG technique can be used for the
estimation of the motor unit size and territory, it is practically most useful for the study
of the neuromuscular transmission. In conclusion, the thorough understanding of the
motor unit physiology and MUP electrophysiology is essential for the correct application
and interpretation of the needle EMG.
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