Interference of rhythmic constraint on gait in healthy subjects and patients with early Parkinson's disease: evidence for impaired locomotor pattern generation in early Parkinson's disease.

Patients in the early stages of Parkinson's disease have been shown to walk slower with smaller steps, resembling the gait of normal elderly subjects, but specific disorders of dynamic equilibrium or rhythmic gait patterning have not yet been identified. In the present study, gait control in 22 healthy subjects and 22 patients with early Parkinson's disease was challenged by means of a paradigm requiring subjects to decrease their step rate (cadence) by 20% in response to a metronome signal (rhythmic constraint). Control subjects and patients were matched for age, sex, and body height. Eleven patients were receiving standard antiparkinsonian therapy and were assessed under their ongoing medication, whereas the remaining 11 patients had not yet been started on dopaminergic therapy ("de novo" Parkinson's disease). Gait parameters reflecting dynamic equilibrium (double-support time) and locomotor patterning (step length, stride duration) were recorded by means of a mechanical device (locometer). Sixteen patients and 16 control subjects were able to accomplish the task. Whereas regulation of step length became irregular during rhythmic constraint in both patients and control subjects, irregular timing of steps was only observed in patients suggesting disturbance of periodic locomotor activity generation.