Cognitive functions in major depression and Parkinson disease.

OBJECTIVE To investigate the importance of major depression in the production of cognitive deficits in patients with Parkinson disease (PD). DESIGN A comprehensive neuropsychological and psychiatric assessment was conducted in 19 patients with PD and major depression, 31 patients with PD without depression, 27 patients with major depression but without PD, and 12 age-comparable healthy controls. SETTING Outpatient clinic. RESULTS Patients with major depression (with or without PD) had significantly more severe cognitive deficits than both healthy controls and patients with PD without depression on tests of verbal fluency and auditory attention, while patients with PD and major depression had significantly more severe deficits on tasks of abstract reasoning and set alternation compared with the other 3 groups. CONCLUSIONS Major depression in patients with PD is associated with significant deficits on specific cognitive tasks. While some of these deficits may be explained by the presence of major depression, frontal lobe-related cognitive impairments may result from an interaction between neuropathologic factors in PD and the mechanism of major depression.