What contributes to depression in Parkinson's disease?

Depression is a common problem in patients with Parkinson's disease, but its mechanism is poorly understood. It is thought that neurochemical changes contribute to its occurrence, but it is unclear why some patients develop depression and others do not. Using a community-based sample of patients with Parkinson's disease, we investigated the contributions of impairment, disability and handicap to depression in Parkinson's disease.

Ninety-seven patients seen in a population-based study on the prevalence of Parkinson's disease completed the Beck Depression Inventory (BDI). Clinical and historical information on symptoms and complications of Parkinson's disease were obtained from the patients by a neurologist. In addition, clinician and patient ratings of disability on the Schwab and England scale were obtained and a quality of life questionnaire was completed.

Moderate to severe depression (BDI > or = 18) was reported by 19.6% of the patients. Higher depression scores were associated with advancing disease severity, recent self-reported deterioration, higher akinesia scores, a mini-mental score of < 25 and occurrence of falls. Disability as rated by the neurologist accounted for 34% of the variance of depression scores. Self-reported impairment of cognitive function and the feeling of stigmatization accounted for > 50% of the variance of depression scores.

Depression in patients with Parkinson's disease is associated with advancing disease severity, recent disease deterioration and occurrence of falls. Regression analysis suggests that depression in Parkinson's disease is more strongly influenced by the patients' perceptions of handicap than by actual disability. The treatment of depression should therefore be targeted independently of treatment of the motor symptoms of Parkinson's disease, and consider the patients' own perception of their disease.