ELECTROMYOGRAPHY OF THE EXTERNAL ANAL-SPHINCTER IN PATIENTS WITH PARKINSONS-DISEASE AND MULTIPLE SYSTEM ATROPHY - FREQUENCY OF ABNORMAL SPONTANEOUS ACTIVITY AND POLYPHASIC MOTOR UNIT POTENTIALS

Electromyographic studies of the external anal sphincter muscle have r eceived increasing attention in the differential diagnosis of patients with parkinsonism. Based on the fact that the external anal sphincter muscle is partly innervated by fibers that originate in Onuf's nucleu s in the segments S2-S4 of the spinal cord, an increased duration of t he motor unit potentials (MUPs) and an increased polyphasia may reflec t neuronal loss of these lower motor neurons characteristic for multip le system atrophy. We report the results of anal sphincter electromyog raphy in 15 patients with clinically probable multiple system atrophy (MSA) and 10 patients with Parkinson's disease (PD). There was no sign ificant difference between patients with MSA and patients with PD conc erning the duration of MUPs, mean number of phases, and rate of polyph asic motor potentials. There was a tendency for a longer mean duration and increased polyphasia in patients with MSA compared to patients wi th PD. Spontaneous activity was recorded in 11 of 15 patients with MSA occurring especially in patients with MSA of the striatonigral type, but not in patients with PD. In this study, the duration of MUPs and t he rate of polyphasia were unreliable criteria in the electrophysiolog ical differential diagnosis of patients with parkinsonism. Abnormal sp ontaneous activity, although difficult to detect, is a more specific m arker for neuronal degeneration of Onuf's nucleus occurring in patient s with MSA. (C) 1997 John Wiley & Sons, Inc.