Assessment methods and factors associated with depression in Parkinson's disease.

Depression is a common problem experienced by patients with Parkinson's disease (PD). Identifying depression in PD is difficult and the determinants of depression in PD are complex and debatable. Here we review our recent studies which have (i) examined the validity of current depression rating scales in PD, (ii) introduced a self-reported and validated strategy to identify a lifetime history of depression in PD, and (iii) investigated genetic and non-genetic factors associated with depression in the context of PD. Our research showed PD-specific cut-off values suitable to use for the Hamilton Depression Scales (HAMD and HDI) and the Geriatric Depression Scale (GDS-15) when dichotomising patients with and without a current depression. Using the GDS-15 specific cut-off scores and a number of self-reported questions that screen for a lifetime history of depression, we developed a novel method to dichotomise PD patients according to current depression or a past history of depression. This method was applied in a large-scale study examining the factors associated with depression in PD. We clarified that the severity of PD is positively related to depression. We also showed that a number of other clinical factors including a longer duration of PD, a younger PD onset age, frequent falls, a history of anxiety disorder and memory problems were associated with depression in PD. In addition to these clinical factors, we observed associations between depression, and lower education levels, a history of smoking and a regular use of non-aspirin bases NSAIDs or analgesics. No associations were found between depression in PD and common genetic variations examined across the serotonin and dopamine transporter genes. Our studies provide a focus for future intervention strategies.