Differential Diagnosis Of Multiple-System Atrophy With Parkinson’s Disease By External Anal- And Urethral-Sphincter Electromyography

BACKGROUND: The differential diagnosis of Parkinson’s disease (PD) with multiple-system atrophy (MSA) is difficult because of their similarity in symptoms and signs. The objective of this study was to investigate the value of external anal-sphincter electromyography (EAS-EMG) and urethral-sphincter electromyography (US-EMG) in differentiating MSA from PD. METHODS: A total of 201 patients, — 101 MSA and 100 PD — were recruited in this study. Average duration and amplitude of motor unit potentials (MUPs), percentage of polyphasic MUPs, amplitude during strong contractions, and recruitment patterns during maximal voluntary contractions were recorded and analyzed to assess diagnostic efficiency of EAS-EMG and US-EMG for MSA. RESULTS: Significant differences in average MUP duration and recruitment patterns during maximal voluntary contractions were found between patients with MSA and patients with PD using both EAS-EMG (P<0.001, P<0.001) and US-EMG (P<0.001, P<0.001). The percentage of polyphasic MUPs and amplitude during strong contractions showed significant differences in MSA and PD using only EAS-EMG (P<0.001, P=0.005). Cutoff points for average MUP duration in EAS-EMG and US-EMG for differential diagnosis of MSA with PD were 10.9 and 11.1 milliseconds, respectively. With average MUP duration of EAS-EMG and US-EMG being applied jointly, sensitivity and specificity in distinguishing MSA from PD were 83.2% and 71.8%, respectively. CONCLUSION: EAS-EMG and US-EMG were sensitive and specific methods for the diagnosis and differential diagnosis of MSA, and the combination of both would improve the diagnostic rate of MSA compared to only one method being used.