Objective: To investigate the importance of major depression in the pr
oduction of cognitive deficits in patients with Parkinson disease (PD)
. Design: A comprehensive neuropsychological and psychiatric assessmen
t was conducted in 19 patients with PD and major depression, 31 patien
ts with PD without depression, 27 patients with major depression but w
ithout 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 con
trols and patients with PD without depression on tests of verbal fluen
cy 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: Ma
jor depression in patients with PD is associated with significant defi
cits on specific cognitive tasks. While some of these deficits may be
explained by the presence of major depression, frontal lobe-related co
gnitive impairments may result from an interaction between neuropathol
ogic factors in PD and the mechanism of major depression.