| Separate studies have described dementia of Parkinson's Disease (PD) as including neuropsychological deficits in memory, executive function, and visuospatial skills. However, it is not known to what extent, if at all, the neuropsychological profile in PD dementia represents a more severe form of the mild cognitive deficits seen in nondemented PD patients. If the pattern of demented patients matches that of the nondemented, in all respects except degree of impairment, then it can be argued that dementia represents a progression of the nondemented state. If dementia is not a simple progression of the deficits of the nondemented state, one or more other processes might be at work, likely involving multiple pathogenetic cascades. These issues have implications for research both into the pathogenesis of, as well as treatment for, Parkinsonian dementia. To address these questions, 23 demented Parkinson's disease patients were tested in multiple cognitive domains and compared to 23 nondemented PD patients, and 23 normal controls. Results were analyzed in terms of differences between groups as well as heterogeneity within the dementia group. The PD demented, PD nondemented, and normal controls groups all had unique neuropsychological profiles. The demented PD group was significantly impaired, compared to both the nondemented group and the normal controls, on all measures, including global intellect, memory, visuospatial, language, attention, and executive functions, with the sole exception of long term memory. Relative deficits, compared to controls, in the nondemented patient group were restricted to episodic memory and visuospatial skills. The memory deficit of the nondemented group, however, was as great as that found in the demented group. A cluster analysis of the demented group identified three neuropsychologically distinct subgroups. Since length of disease, age, and motor status failed to differentiate these clusters it is likely that these are not different disease stages, but rather neuropsychologically distinct subgroups of dementia in Parkinson's disease. Therefore, these findings suggest that dementia in PD is not a simple progression of cognitive deficits, but a separate and distinct process. Current results suggest the presence of three different neuropsychological profiles in this sample. |
