Number of potential reversals (turns) and amplitude of the pattern of electrical activity of the abductor pollicis brevis muscle in patients with neurogenic diseases.

We have quantified the pattern of electrical muscle activity at a force of 0.3 kg, 30% of maximum force, and maximum force in the abductor pollicis brevis muscle of 21 patients with neurogenic disorders (10 with carpal tunnel syndrome, 9 with polyneuropathy and 2 with motor neurone disease) and of 15 normal subjects. In normal subjects, the number of turns, the mean amplitude and the ratio between them were independent of maximum force, age and sex of the subjects. In 21 patients with neurogenic disorders, the cumulative diagnostic yield of the analysis of the pattern of electrical activity was 86% compared to the diagnostic yield of the mean duration and mean amplitude of individual motor unit potentials of 90%. These diagnostic yields in a small distal muscle were of the same order as those of the brachial biceps muscle in previous studies.