Receiver operating characteristic analysis of sphincter electromyography for parkinsonian syndrome

We performed receiver operating characteristic (ROC) analysis to determine the ability of sphincter electromyography (EMG) to distinguish multiple system atrophy (MSA) from other parkinsonisms. The following was determined: (1) the appropriate motor unit potential (MUP) parameter among duration, phase, and amplitude; (2) the desirable parameter of our duration criteria; that is, more than 20% MUPs having >10 ms duration (criteria a) or mean duration >10 ms (criteria b).

We retrospectively reviewed 441 case records where sphincter EMG were performed in patients with parkinsonian syndromes: MSA, n = 263; Parkinson's disease, n = 129; dementia with Lewy bodies, n = 25; and progressive supranuclear palsy, n = 24. We performed ROC analysis of the data sets.

The area under the curve used to differentiate MSA from other parkinsonian syndromes was 0.68 in duration, 0.57 in phase, and 0.51 in amplitude, respectively; these values were statistically significant. With regard to our duration criteria, area under the curve was 0.69 for the average duration of MUPs (criteria b) and 0.67 for percentage of MUPs of duration >10 ms (criteria a); these values were also statistically significant.

This study suggests that duration is appropriate parameter for the differentiation of MSA. However, the area under the curve of the mean duration was insufficient to confirm the diagnosis; sphincter EMG should be used as a supportive diagnostic tool for the diagnosis of MSA.