Anal sphincter EMG does not distinguish between multiple system atrophy and Parkinson's disease

Clinical distinction of multiple system atrophy (MSA) from Parkinson's dise ase (PD) is often difficult. Several recent reports indicate that objective classification may be accomplished using electromyographic (EMG) testing o f the anal or urethral sphincters, but some authors have found that these a re not reliable for this purpose. We studied 13 patients with PD and 10 wit h probable MSA as diagnosed by consensus of four movement disorders specali sts, according to accepted clinical criteria. Anal sphincter EMG was perfor med blind to the clinical diagnosis. We found no significant differences in the mean duration of motor unit potentials (MUPs), mean MVP amplitude, or prevalance of polyphasic potentials, satellite potentials, very long durati on MUPs, or spontaneous activity between the two groups Thus, anal sphincte r EMG does not differentiate between PD and MSA. MSA. (C) 200 John Wiley & Sons, Inc.