Early-occurrence of manual motor blocks in Parkinson's disease: A quantitative assessment

Objectives - Quantitative analysis of internally-cued, repetitive motor performance in patients with Parkinson's disease (PD). Material and methods - Computerized quantitative measurements of the frequency, duration and temporal profile of manual motor blocks (MMBs) during performance of a manual tapping task, in 39 patients with PD, as compared to 17 age-matched healthy controls. Results - Performance of PD patients was markedly abnormal both quantitatively and qualitatively, as reflected by an increase (7.0% vs 4.6%) in MMBs, and by their occurrence from onset of movement. The phenomenon was already observed in the early stages of the disease, and was also correlated with the occurrence of freezing of gait. A standard levodopa-carbidopa (125- 12.5 mg) dose only partially affected this phenomenon. Conclusions - Augmented motor blocks in internally-cued performance should be recognized as a frequent, distinct and generalized feature of PD. Whereas the gait disorder is regarded as characteristic of the advanced stage of PD, our findings suggest that the basic defect in internal rhythm formation can be detected by sensitive measurement tools from the early stages of the disease. In addition, the methodology developed in this study to quantitatively measure manual motor blocks may be a useful tool for future development of therapeutic regimens for this debilitating aspect of motor dysfunction in PD.