EMG and histochemical findings in neurogenic atrophy with electrode localisation.

A new technique permitting electromyographic electrode localisation during open muscle biopsy is described. Using this technique recordings were made from biceps brachii from 22 normal subjects and 19 patients with neurogenic atrophy. Motor unit potential duration and onset interspike interval were the best predictors of histochemical evidence for atrophy. Of patients with neurogenic atrophy, polyphasic potentials and increased rise time of the major spike were found in 18 and 10 cases respectively. Abnormal motor unit potentials were always associated with findings of atrophy. However, normal duration, amplitude, and recruitment intervals occurred in 36%, 58% and 50% respectively of subjects with neurogenic atrophy in the region of the recording.