Subtypes of Parkinson's disease defined by intellectual impairment.

Sixty patients with Parkinson's disease were administered a battery of neuropsychological tests. Using regression data from a matched normal control sample, age- and education-residualized test scores were obtained for the patients. Three clusters of patients were identified: those with both verbal memory and visuospatial reasoning disorders (n = 24), those with memory impairment only (n = 17) and those with normal intellectual function (n = 12). Analysis of variance and planned comparisons (Newman-Keuls) were performed to detect group differences. No difference on 9 memory measures were found between the 2 memory-impaired groups. However, these groups differed significantly on all memory measures from the group with normal function. The 2 memory-impaired groups also differed significantly from each other on all 7 measures of visuospatial reasoning. The group with memory loss only was significantly younger than the group with both visuospatial and memory impairment and also demonstrated less bradykinesia. Otherwise, there were no group differences in the severity of motor signs, disease duration or duration of levodopa therapy. These findings support a different etiology for motor and intellectual deficits in Parkinson's disease.