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Central nervous system amplification

Its potential in the diagnosis of early multiple sclerosis

Department of Medicine, Division of Neurology, the University of British Columbia, and Department of Diagnostic Neurophysiology, Vancouver General Hospital, Vancouver, B.C.

Ability to record a sizable somatosensory evoked potential (SEP) in the absence of a recordable sensory nerve action potential (SNAP) suggests a normally occurring central nervous system amplifying process. Increments in SEP and SNAP amplitude with increasing stimulus strength between threshold and 2.5 times threshold (maximum) were compared. At threshold (40% of maximum stimulus) and 50% maximum stimulus, amplification measured 2.3 ± 0.7 and 2.0 ± 0.6, respectively. In 21 MS patients, the SEP at threshold stimulation was absent in 15, but normal in 5 of these at maximum stimulation. It is postulated that normal central amplification is markedly attenuated in MS, and this may be a sensitive indicator of early disease.

Address correspondence and reprint requests to Dr. Eisen, Diagnostic Neurophysiology—EMG, Vancouver General Hospital, 855 West 12th Avenue, Vancouver, B.C., Canada V5Z 1M9.

Supported by the Multiple Sclerosis Society of Canada.

Accepted for publication September 21, 1981.

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