Evoked muscle action potentials in patients with muscular dystrophy.

Electromyographic study of evoked muscle action potentials was made in a group of 31 patients with muscular dystrophy. Potentials, recorded with bipolar needle electrodes, were evoked by supramaximal stimuli applied to the motor nerve. The potentials recorded in 21 (67.7%) patients appeared markedly polyphasic, with a considerable degree of temporal dispersion. In general, the average number of phases was 20.9 +/- 9.08; the average duration attained 29.1 +/- 10.57 msec. The latency for the first component of the potentials and the motor conduction velocity along the main trunks were normal. The polyphasic potentials of dystrophic patients were similar to the MAP evoked in neuropathic patients. It is concluded that the long-lasting polyphasic potentials of dystrophic patients may represent the involvement of the thin peripheral branches of motor nerves in the pathologic process.