Depression in the patient with Parkinson's disease.

Depression is the most commonly encountered mental change in patients with Parkinson's disease. However, its cause is controversial and little is known about its natural history. Some view depression as reactive to the physical disability inherent to Parkinson's disease; however, others view the depressive disorder as the direct result of underlying biochemical changes caused by the disease process. Abnormalities within the serotonin metabolic pathway have been observed in depressed patients with Parkinson's disease and may help to explain why this form of depressive disorder is so common and persistent. Other forms of depression share this biochemical alteration. Attempts to alleviate depression with serotonin agonists have proven successful. Current research efforts are exploring biological aspects of depression in Parkinson's disease and the epidemiology of this disorder as a model of depression in the elderly, medically ill patient.