There is an increasing awareness that non-motor symptoms in Parkinson’s disease have a significant impact on quality of life and caregiver burden. Depression, often accompanied by anxiety, affects at least a third of all patients during the course of the disease and is associated with poor prognosis. Not only are patients with depression more likely to be affected by cognitive problems such as poor memory, they are also known to be at higher risk of requiring nursing home placement.

While the cause of depression in Parkinson’s disease is not well understood, it is likely to be due to a number of factors. It does appear that depressive symptoms are not simply due to a reaction by the individual to their levels of physical disability. Indeed there is strong evidence to suggest that mood disturbances may predate the manifestation of motor symptoms by up to several years. This suggests that biochemical disturbances that result from early cell loss in Parkinson’s may cause depression, which could therefore represent a possible target for detecting pre-morbid disease.

There is also an emerging literature exploring the phenomenon of heterogeneity in Parkinson’s disease, which characterises differing sub-groups of patients by their predominant disease symptoms. Such work has identified that depression appears to be more common in patients with the specific motor symptoms of bradykinesia and rigidity, rather than those patients who are more troubled by tremor. This work again raises the likelihood that underlying pathological changes are responsible for the feature of depression.