Cognition in Parkinson's Disease: an examination of clinically meaningful subgroups
Miller, Ivy N
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The nature and progression of cognitive change in Parkinson's disease (PD) are not well understood and may depend on subgroup membership. Though investigators have examined subgroups with respect to cognition, most use limited neuropsychological assessments and do not account for important disease and participant characteristics. The present series of studies was designed to systematically examine potentially informative subgroups. Cognition, mood and quality of life were evaluated in 65 nondemented PD patients and 54 age- and education-matched healthy control participants (HC). Neuropsychological measures of executive, visuospatial, memory and psychomotor function, as well as questionnaires of mood, anxiety, daily functioning and quality of life were administered to all participants. The first study compared motor subtype measurement methodologies and examined the differential value of tremor vs. non-tremor motor subtypes in understanding PD-related cognition. The patients with non-tremor but not tremor motor subtype performed significantly worse than HC on tests of executive, visuospatial, and psychomotor function, and endorsed more anxiety. The second study compared men and women with PD to HC men and women on cognition and mood, and compared men and women with PD on quality of life and motor, vision and activities of daily living. Gender was unrelated to any clinical or mood variable or to performance on most cognitive tests. The third study compared PD and HC on cognitive abilities known to be supported by frontal- vs. posterior-cortical lobes in order to determine the usefulness of considering type of neuropsychological deficit as an indicator of disease status. Half the PD participants were categorized in a deficit group based on performance of the frontaland posterior-type tests, and several more exhibited deficits at a sub-threshold level. Examination of individual test performance highlighted executive-function and psychomotor tests that were particularly sensitive to cognition in PD. Taken together, these studies suggest that motor subtype and frontal-posterior cortical subtype but not gender may be important to understanding cognition in highfunctioning, non-demented PD patients. This information may be applicable to investigations of the nature and progression of cognitive change in this disorder.
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