Cognitive impairment in Parkinson's disease: a 6year follow-up study

Parkinson's disease (PD), originally characterized as a motor disorder, has received increasing attention for its cognitive deterioration. Both positive and negative correlations between motor disability and cognitive disorders have been reported. To clarify the nature of the relationship between motor disability and cognitive impairment, we examined event-related potentials (P300) and cognitive state in 29 non-demented patients with Parkinson's disease, together with changes in the degree of motor disability over a period of 6years. Over the 6year period, the peak latency of P300 became longer when motor activity deteriorated from the Hoehn and Yahr stage II to stage III, or from stage III to stage IV. The cognitive state in PD patients was characterized by the impairment of attention/calculation and of constructional ability in categories of the Folstein Mini-Mental State examination. The degree of impairment of these items deteriorated in proportion to the progression of motor disability. The disruption of some neuronal loops related to both P300 latency and cognitive functions, such as attention/calculation and visuospatial ability, became prominent with the deterioration of motor ability in PD patients.