Depression in patients with early versus late onset of Parkinson's disease.

We examined correlates of depression in patients whose onset of Parkinson's disease (PD) began before age 55 (early-onset group) compared with patients whose onset was after age 55 (late-onset group). The early-onset group showed a significantly higher frequency of depression than the late-onset group. When both groups were matched for duration of the disease, the early-onset group still showed a significantly higher frequency of depression, whereas tremor, akinesia, and rigidity were significantly more severe in the late-onset group. A stepwise regression analysis showed that in the early-onset group, depression scores were significantly correlated with scores of cognitive impairment and duration of the disease, while in the late-onset group, depression scores were significantly correlated with impairments in activities of daily living. These data suggest that depression in patients with early-onset PD may have a different etiology than in patients with late-onset PD.