Chapter 4 . 1 Clinical EMG and glossary of terms most commonly used by clinical electromyographers

Electromyography is best regarded as an extension of the clinical neurological examination and taken outside this context results are often meaningless and dif®cult to interpret. Test design must be based upon the clinical problem if the most comprehensive and valid information with a minimum number of procedures is to be achieved, and predetermined stereotyped protocols should be discouraged. However, the standards within a particular technique used (needle EMG, nerve conduction) should be rigidly adhered to if results are to be reproducible Clinical application of electromyography dates back to the 1930s. Lindsley (1935) described variations of motor unit potential amplitude during voluntary muscle activity in a patient with myasthenia gravis, and in 1938 Denny-Brown and Pennybacker (1938) described ®brillation and fasciculation spontaneous potentials in denervated muscles. Over subsequent years technology improved allowing more con®dent differentiation between myopathic and neurogenic disorders, the ability to detect subclinical disorders, assessment of the extent and the severity of a lesion, accurate localization of the site of the lesion and in many cases offering a reasonable differential diagnosis. Major contributors to electromyography during its developmental years were Kugelberg (1947, 1949) in Stockholm, who described the motor unit changes in neuromuscular disorders, and Buchthal and his co-workers in Copenhagen (Buchthal and Clemmesen 1941; Buchthal et al. 1957) who quantitatively measured the motor unit. Later, Ekstedt, StaÊlberg and their associates (Ekstedt 1964; Ekstedt and StaÊlberg 1973; StaÊlberg et al. 1974) devised single ®bre electromyography (SFEMG), which proved to be very useful in ``morphological'' characterization of the motor unit. Subsequently macroand scanning-electromyography enabled measurement of the entire motor unit in a three-dimensional plane (StaÊlberg 1980). Other important steps 189 Recommendations for the Practice of Clinical Neurophysiology: Guidelines of the International Federation of Clinical Physiology (EEG Suppl. 52) Editors: G. Deuschl and A. Eisen q 1999 International Federation of Clinical Neurophysiology. All rights reserved. Published by Elsevier Science B.V.