Parkinson's disease. Cognitive changes in relation to treatment response.

Four groups of patients with Parkinson's disease matched for age, education and IQ were categorized by response to treatment and compared with a normal control group. The patient groups were (1) No Treatment (de novo); (2) Good Response (including minor fluctuations in symptoms); (3) Fluctuations (significant, including 'on-off' phenomena) and/or marked Abnormal Involuntary Movements (dyskinesias); and (4) Poor Response ('secondary treatment failure' characterized by significant deterioration over time in all major symptoms). As a previous investigation had established that neuropsychological tests thought to be sensitive to the functional integrity of the frontal lobes are selectively impaired in Parkinson's disease, the first phase of this study compared the five groups on five such tests and two tests of psychomotor ability. While all patient groups displayed deficits on the psychomotor tests and on several tests associated with frontal lobe function compared with normals, only the Poor Response group was impaired on all tasks. In a second phase, comprehensive testing of additional cognitive processes such as attention, mnemonic, and visuospatial functions, the latter two traditionally thought to depend primarily on posterior cortical regions, revealed no significant cognitive deficits in any patient group. Results are discussed with respect to the involvement of the nigrostriatal and mesocortical dopaminergic systems.