Quantitative electromyography of the external anal sphincter in Parkinson's disease and multiple system atrophy

The distinction of multiple system atrophy (MSA) from Parkinson's disease ( PD) can be difficult, especially early in the disease. In MSA degeneration of sacral anterior horn cells (Onuf's nucleus) results in denervation-reinn ervation of anal and urethral sphincter muscles, which can be recognized as neurogenic electromyographic (EMG) changes of motor unit potentials. Sphin cter EMG has therefore been recommended as a test for distinguishing MSA fr om PD, Our results confirm the presence of marked neurogenic EMG changes of the external anal sphincter muscle in patients with probable MSA compared to healthy controls. However, in patients with probable PD, our quantitativ e EMG data show a scatter from normal to marked neurogenic changes and the degree of EMG abnormality is correlated to the duration of the disease. Thu s an abnormal sphincter EMG cannot be taken as a strong indicator of MSA ra ther than PD in the individual patient, especially in long-standing cases, (C) 2000 John Wiley & Sons, Inc.