The Utility of Post-Void Residual Volume versus Sphincter Electromyography to Distinguish between Multiple System Atrophy and Parkinson’s Disease

OBJECTIVE To determine the ability of sphincter electromyography (EMG) and post-void residual urine volume (PVR) during a free-flow study and a pressure-flow study (PFS) for distinguishing multiple system atrophy (MSA) from Parkinson's disease (PD). METHODS We retrospectively reviewed 241 case records; both urodynamic study and sphincter EMG were performed in patients with MSA (n = 147) and PD (n = 94). RESULTS There was a statistically significant difference (p < 0.01) in the mean PVR during the free-flow study (113.1 ± 7.5 mL in MSA and 40.4 ± 3.8 mL in PD), mean PVR during PFS (230.1 ± 12.6 mL in MSA and 71.7 ± 6.6 mL in PD), and mean duration of MUP for sphincter EMG (9.3 ± 0.1 ms in MSA and 7.7 ± 0.1 ms in PD). The area under the curve used for differentiating MSA from PD was 0.79 and 0.73 for PVR during PFS and the free-flow study, respectively. There was a mean duration of 0.69 ms for the sphincter EMG. CONCLUSIONS The present results suggested that PVR was more appropriate than sphincter EMG for differentiating MSA from PD.