Depression and cognitive impairment in Parkinson's disease.

Neuropsychological deficits including cognitive impairment as well as depression are among the most frequent and important mental disorders found in patients with Parkinson's disease (PD). It has never been determined, however, whether there is a specific relationship between cognitive impairment and depression. A consecutive series of patients with PD was therefore examined for the presence of depression and neuropsychological deficits. Severity of depression was found to be the single most important factor associated with the severity of cognitive impairment. When PD patients with major depression were compared with an age and stage-matched group of nondepressed patients with PD using a neuropsychological battery, major depressed patients performed significantly worse than the nondepressed patients on all aspects of neuropsychological function tested. These impairments were most pronounced on frontal lobe tasks.