Parkinson’s disease (PD) affects approximately 1 million individuals in the US. Depressive symptoms occur in approximately half of PD patients and are a significant cause of functional impairment.

Methodology: A computer-based search of the literature, augmented by extensive bibliography-guided article reviews, was utilized to find data on depression and Parkinson’s disease. Twenty articles were reviewed using evidence-based methods. Reviewed topics include PD, depression, neurodegeneration in PD patients, onset of depression in PD, and treatment of depression in PD patients.

Results: Postmortem and imaging studies have correlated clinical symptoms of depression with the non-motor basal ganglia-thalamic-frontal cortex circuit. PD patients with comorbid depression have smaller subcortical nuclei which is similar to non-PD patients with depression. Changes in both the serotonin and dopamine systems have been implicated in depression. Decreased numbers of serotonin neurons in the dorsal raphe nucleus and dopamine neurons in the ventral tegmental area are found postmortem in PD patients with a history of depression.

Conclusion: There is accumulating evidence suggesting that depression in PD is secondary to the underlying neuroanatomical degeneration, as well as a reaction to the psychosocial stress and disability of the PD diagnosis.