Frequency of Depressive Disorders in Parkinson's Disease: A Systematic Review and Meta-Analysis

Background: Depressive disorders are recognized as a common neuropsychiatric disorder of Parkinson's disease (PD). Reported frequencies vary widely among studies and depend on the diagnostic criteria, the methods of ascertainment used, and the population sampled. Objective: We aimed to evaluate the frequency of depressive disorders in PD and to investigate the relationship with PD clinical variables. Methods: A systematic review and meta-analysis of observational studies (community-based, prospective and retrospective cohort, case-control, and cross-sectional studies) reporting the frequency of depressive disorders in PD patients. Results: Electronic database search wielded 3,536 articles; an additional 91 were identified through citation chaining. 163 full-text articles were assessed for eligibility. Of these, 49 met the inclusion criteria for our analysis. The pooled frequency of depressive disorders was 30.7% (95% confidence interval [CI] 25.6 to 36.2; I-2 = 95%; 49 studies; combined n = 10,039). The pooled frequency of major depressive disorder was 14.0% (95% CI 10.5 to 18.5; I-2 = 88%; 23 studies; combined n = 5,218). Subgroup/meta-regression analyses were conducted to investigate the relationship between frequency and study inclusion criteria, methodology used for diagnosis, and study design. We found a statistically significant correlation between study design and depressive disorders frequency (ranging from 8% in the community-based study to 44% in the retrospective studies) and a statistically significant positive correlation between mean baseline PD duration and major depressive disorder frequency. Conclusion: The current meta-analysis found a global frequency of depressive disorders of 30.7% and major depressive disorder of 14.0%. Study design influenced the frequency of depressive disorders in PD. Mean baseline PD duration and major depressive disorder frequency were positively correlated.