Is freezing of gait in Parkinson's disease related to asymmetric motor function?

Freezing of gait (FOG) is a disabling phenomenon common in patients with advanced Parkinson's disease (PD). The cause of FOG is unclear. The objective of this study was to explore a novel hypothesis stating that FOG is related to asymmetric motor performance. We compared PD patients that experience FOG episodes (PD+FOG) with PD patients that do not (PD-FOG) and studied the relationship of FOG to asymmetry in gait and in rhythmic hand movement performance to determine whether potential FOG-related gait asymmetry is unique to walking or whether it is systemic. Subjects were tested in an "off" (unmedicated) and again in an "on" (medicated) state. Gait was more asymmetric in PD+FOG than in PD-FOG during "off" state (p = 0.005) and during "on" (p = 0.016). Rhythmicity of foot swing in one leg was correlated with the other leg in PD-FOG but not in PD+FOG. There was no difference in asymmetry in performance of rhythmic hand movements between the two groups. No correlation was found between asymmetry of clinical symptoms and gait asymmetry. Taken together, the results of this study suggest that bilateral uncoordinated gait and marked gait asymmetry, but not asymmetry in motor performance in general, are associated with FOG.