Higher incidence of depression preceding the onset of Parkinson's disease: a register study.

Although case histories of depression preceding Parkinson's disease (PD) point to a possible pathophysiological relationship between these two disorders, there is as yet no epidemiological evidence to support this view. We compared the incidence of depression in patients later diagnosed with PD with that of a matched control population. Using data from an ongoing general practice-based register study, the lifetime incidence of depressive disorder was calculated for patients until their diagnosis of PD and compared with that of a matched control population from the same register. At the time of analysis, the register held information on 105416 people. At the time of their diagnosis of PD, 9.2% of the patients had a history of depression, compared with 4.0% of the control population (chi(2) = 22.388, df = 1, P < 0.001). The odds ratio for a history of depression for these patients was 2.4 (95% CI: 2.1-2.7). We concluded that the higher incidence of depression in patients who were later diagnosed with PD supports the hypothesis of there being a biological risk factor for depression in these patients. Copyright 2003 Movement Disorder Society