Parkinson's disease and depression: the relationship to disability and personality.

In a study of 104 patients with Parkinson's disease (PD) and 61 control subjects with equal disability scores, PD patients had higher depression scores (P < 0.001) than control subjects. Functional disability was correlated with depression in PD and, in a regression analysis, explained 9% of the variance in depression (P < 0.001). Depression was not correlated with novelty seeking, a personality trait related to dopaminergic pleasure and reward systems. Harm avoidance, a trait related to central serotonergic systems, was, however, correlated with depression (P < 0.001) and explained 31% of the variance in depression scores. Results support the hypotheses that both physiologic and psychologic factors contribute to depression seen in these patients and that serotonergic function plays a more critical role than dopaminergic function.