Variability of EMG patterns: a potential neurophysiological marker of Parkinson's disease?

OBJECTIVE: This study evaluated whether changes in the electromygraphic (EMG) pattern during rapid point-to-point movements in individuals diagnosed with PD can: (1) distinguish PD subjects from healthy subjects and (2) determine if differences in the EMG pattern reflect disease severity in PD. METHODS: Three groups of 10 PD subjects and 10 age/sex-matched healthy subjects performed rapid 72 degree point-to-point elbow flexion movements. PD subjects were divided, a priori, into three groups based upon off medication motor UPDRS score. RESULTS: Measures related to the EMG pattern distinguished all PD subjects and 9 out of 10 healthy subjects, resulting in 100% sensitivity. Further, significant correlations were shown between EMG measures and the motor UPDRS score. After 30 months, the one healthy subject whose EMG pattern was abnormal was reexamined. The EMG measures remained abnormal and the motor UPDRS score went from 0 to 10. Parkinson's disease was diagnosed. CONCLUSION: Measures related to the variability of the EMG pattern during rapid point-to-point movements provide neurophysiological measures that objectively distinguish PD subjects from healthy subjects. These measures also correlate with disease severity. SIGNIFICANCE: EMG measures may provide a non-invasive measure that is sensitive and specific for identifying individuals with PD.