Effect of age at onset on frequency of depression in Parkinson's disease.

In a consecutive series of 169 outpatients with Parkinson's disease the frequency of depression was compared in two groups: those who developed Parkinson's disease before the age of 50, and those who developed the disease after 50. Major depression was found in 36% of patients with early onset and in 16% of patients with late onset Parkinson's disease. This significant difference disappeared when both groups were matched for duration of Parkinson's disease. A stepwise regression analysis in both the early onset and the late onset Parkinson's disease showed a significant correlation only between depression scores and the impairment scores of activities of daily living.