Depression is a common complication of PD that negatively influences patient and caregiver quality of life (QOL),
and is associated with a worsening of disease symptoms, a more rapid decline in health status, high psychiatric
comorbidity, and increased caregiver burden. Symptoms of depression in patients with PD tend to occur at two
time points: near the time of diagnosis and later in the disease as disability and impairment increases. Depression in
early PD may be associated with the emotional adjustment to having a chronic, progressive disease, while depression
late in PD is likely related to biochemical or degenerative changes related to PD (e.g., a deficiency in dopamine,
serotonergic system dysfunction).