The significance of motor (a)symmetry in Parkinson's disease.

This study was undertaken to evaluate whether the predominant motor distribution pattern (ie, symmetric or asymmetric) observed in patients with Parkinson's disease (PD) contributes independently to disease severity and progression. We further examine whether this pattern is stable over time, and whether a potential change in pattern affects the course of the disease. We used data from the longitudinal PROPARK study (N > 400) to examine the association of the predominant motor distribution pattern with motor, cognitive, depressive, psychotic, and autonomic symptoms, and with excessive daytime sleepiness. We found that a symmetrical distribution of motor features was associated with poorer performance on nearly all domains, but that this was entirely explained by confounding, in particular by higher age and longer disease duration. We also found that greater asymmetry was associated with younger age, younger age at onset, and shorter disease duration. We further observed a clear tendency to develop a more symmetric distribution pattern as the disease advanced. Conversion to a symmetric pattern was associated with more severe disease, but this conversion did not contribute independently to the less favorable disease course. With increasing age and disease duration comes a clear tendency to develop a more symmetric distribution of motor features in PD. Although this change in distribution pattern is associated with more severe disease as compared with nonconvertors, this pattern change did not contribute independently to the less favorable course. We discuss these findings in light of the evidence from the literature.