Arm swing asymmetry in Parkinson's disease measured with ultrasound based motion analysis during treadmill gait

The reduction of arm swing during gait is a frequent phenomenon in patients with early Parkinson's disease (PD). However, the objective quantification of this clinical sign using treadmill-based gait analysis has not been systematically evaluated so far. We simultaneously measured ultrasound based limb kinematics and spatiotemporal gait parameters during treadmill walking at different speeds in 21 early PD patients in Hoehn and Yahr (HY) stage I, 19 patients with bilateral PD in HY stage II and 25 age-matched controls. Both PD groups showed a highly significant reduction of the arm swing amplitude on the more affected body side (MAS). Decomposing total arm swing resulted in a bilateral decrease of arm retroversion in both PD groups, whereas anteversion was normal on the less affected side of the HY I cohort. Early stage patients exhibited a highly significant, almost threefold increase of the arm swing asymmetry index (I(A)) compared with controls. Reduced retroversion on the MAS and increased arm swing I(A) were the independent variables with the closest association to disease status in a multivariate logistic regression analysis. We conclude that ultrasound based motion analysis during treadmill walking allows reliable investigation of asymmetric arm movements in early PD patients which attenuate with ongoing disease. Impaired active arm retroversion seems to be the earliest sign of upper extremity dysfunction in parkinsonian gait. The measurement of limb kinematics during treadmill gait can broaden our methodological line-up for the analysis of complex motor programs in movement disorders.