Comparative analysis of gait and speech in Parkinson's disease: hypokinetic or dysrhythmic disorders?

Gait and speech are automatic motor activities which are frequently impaired in Parkinson's disease. Obvious clinical similarities exist between these disorders but were never investigated. We propose to determine whether there exist any common features in Parkinson's disease between spatiotemporal gait disorders and temporal speech disorders. Gait and speech were analysed on 11 Parkinsonian patients (PP) undergoing deep-brain stimulation of the subthalamic nucleus (STN-DBS) and 11 control subjects under three conditions of velocity (natural, slow and speed). The patients were tested with and without L-dopa and stimulator ON or OFF. Locomotor parameters were recorded using an optoelectronic system. Speech parameters were recorded with a headphone while subjects were reading a short paragraph. The results confirmed that PP walk and read more slowly than controls. Patient's difficulties in modulating walking and speech velocities seem to be due mainly to an inability to internally control the step length and the interpause-speech duration (ISD). STN-DBS and levodopa increased patients' walking velocity by increasing the step length. STN-DBS and levodopa had no effect on speech velocity but restored the patients' ability to modulate the ISD. The walking cadence and speech index of rythmicity tended to be lower in patients and were not significantly improved by STN-DBS or levodopa. Speech and walking velocity as well as ISD and step length were correlated in both groups. Negative correlations between speech index of and walking cadence were observed in both groups. Similar fundamental hypokinetic impairment and probably a similar rhythmic factor similarly affected the patients' speech and gait. These results suggest a similar physiopathological process in both walking and speaking dysfunction.