The role of gait rhythmicity and bilateral coordination of stepping in the pathophysiology of freezing of gait in Parkinson's disease

Freezing of gait (FOG) is a disabling episodic gait disturbance that is common among patients with Parkinson's disease (PD). In this review, we describe a new approach for understanding the mechanisms underlying this puzzling phenomenon. We propose that impairments in the ongoing regulation of gait, even during periods in which freezing is not present, set the stage for the occurrence of a FOG episode. More specifically, three "interictal" walking attributes are associated with FOG: gait rhythmicity, gait asymmetry, and bilateral dyscoordination of left-right stepping. Gait is less rhythmic, more asymmetric, and less coordinated among PD patients with FOG, when compared with PD patients without FOG. We describe the relationship between these changes and other features of patients with FOG and discuss whether these gait changes may predispose to FOG or if they also cause FOG, perhaps, when they are altered beyond a certain threshold or exacerbated by another trigger.