Sex Differences in Motor Unit Behavior in Patients With Parkinson's Disease

The aim of this study was to determine whether there are sex differences in motor unit firing behavior in patients with Parkinson's disease. Twenty-seven patients with Parkinson's disease (females = 14 [age = 71.1 ± 6.8], males = 13 [age = 69.2 ± 10.3], Unified Parkinson's Disease Rating Scale Part III score; females = 10.8 ± 4.8, males = 11.4 ± 1.4) performed a contraction at 30% of the maximal voluntary contraction. For each participant, motor unit spike trains were decomposed from high-density surface electromyography data recorded from bilateral vastus lateralis muscles via blind source separation algorithms. In addition to the mean discharge rates, persistent inward currents were estimated via a paired motor unit analysis. Females presented significantly greater laterality of discharge rate (p = 0.001) and persistent inward currents (p = 0.0121) than males. A significant correlation was observed between the discharge rate and the recruitment threshold on the bilateral side of males and the less-affected side of females but not on the more-affected side of females. These findings indicate that sex differences in motor unit behavior exist in Parkinson's disease patients. Motor unit behavior may be a sensitive and quantitative evaluation tool to highlight differences in disease presentation between males and females.