Quality of life and depression in Parkinson's disease.

This paper reviews the literature on health-related quality of life (Hr-QoL) and depressive disorders, and the relationship between them, in patients with Parkinson's disease (PD). PD is associated with reduced Hr-QoL, including motor and non-motor physical consequences of the disease, emotional well-being and social functioning. While this effect is greater in advanced disease stages, there is no close relationship between disease duration and impact on quality of life, and the relationship between clinical rating scales and Hr-QoL scores is only moderate. On the other hand, presence and severity of depression in PD strongly correlates with Hr-QoL scores, and a number of studies have reported depression as the main determinant of poor HR-QoL scores. Despite being the main determinant of poor Hr-QoL and being recognized as an important problem by clinicians, until recently depression in PD has received relatively little attention in research studies. It is known that depression and anxiety occur more frequently in PD than in controls. Depression occurs in a bimodal pattern in PD, with increased rates at the onset and a later peak in advanced disease. Both anxiety and depression can also occur before the first motor symptoms of PD and predate the diagnosis of PD, indicating that these co-morbidities are manifestations of the underlying disease process of PD. Imaging studies have demonstrated abnormalities of dopaminergic, noradrenergic and serotonergic functioning with some correlation with severity of depression. The overall relationship between disease severity and rate of depression (except for off-period related depression) is poor, suggesting that nigrostriatal dysfunction alone is not sufficient to explain depressive symptoms in PD. Other factors are likely to contribute to occurrence and severity of depression in PD, either due to extrastriatal pathology or due to psychological and environmental factors leading to reactive depression. Thus, it is likely that depression in PD is multifactorial. The investigation of depression in PD is complicated by diagnostic difficulties in measuring and diagnosing depression in patients with PD due to the considerable overlap between symptoms of PD and depression. While a number of treatment approaches have been suggested, double-blind randomized controlled trials to demonstrate improvement of depression and overall Hr-QoL in PD are warranted.