Cognitive impairments in different stages of Parkinson's disease.

A consecutive series of 94 patients with Parkinson's disease (PD) were evaluated for the presence of depression and neuropsychological deficits. Patients were divided into groups based on the severity of their PD symptoms and then further subdivided into depressed and nondepressed groups. Both stage of PD and existence of depression had significant effects on neuropsychological performance. The nondepressed group with severe symptoms showed deficits in cognitive tasks involving motor speed, and the depressed patients with severe symptoms demonstrated impairments in frontal-lobe-related tasks.