Probing motor dynamics at the muscle level—Acoustic myography in Parkinson's disease

Acoustic myography (AMG) noninvasively probes muscle activity. We explored whether AMG captures abnormal motor activity in patients with Parkinson's disease (PD) and how this activity is modulated by antiparkinsonian medication. Twenty patients with PD underwent AMG of the biceps, triceps, extensor carpi radialis longus, and adductor policis muscles of the more affected arm during active and passive movements, using a mobile AMG device (CURO, Denmark). AMG and assessment of motor symptoms were performed in a pragmatic off‐medication state, as well as one and 3 h after oral intake of 200 mg levodopa. Three AMG parameters were calculated using the CURO analysis system. Motor efficiency was expressed by the E‐score, muscle fiber recruitment by the temporal T‐score, spatial summation by the S‐score, and S/T ratio. Twenty age‐ and sex‐matched healthy subjects served as controls. Group mean values were statistically compared using unpaired two‐tailed adjusted t‐test and ANOVA with Tukey´s correction for multiple comparison (p ≤ 0.05). For the biceps and extensor carpi radialis longus muscles, the active movement S:T ratio was lower in PD relative to healthy controls. The E‐score was also lower during active and passive flexion/extension movements in the off‐medication state. No significant between‐group differences in the AMG scores were noted for the triceps muscle during active or passive movements. The active S:T ratio and the E‐score during active elbow flexion and extension may offer a useful means to quickly assess abnormal motor activity and the effect of drug treatment in PD.