Constipation in Parkinson's Disease: A Systematic Review and Meta-Analysis

Introduction: Constipation is a common nonmotor symptom of Parkinson's disease (PD) and has been reported to increase the risk of developing PD. However, previous studies have yielded conflicting results. Understanding this correlation may promote early diagnosis and treatment of PD, which could help patients improve their quality of life. This study aimed to investigate the association between constipation and PD onset. Methods: The study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Meta-analyses of Observational Studies in Epidemiology (MOOSE) guidelines. We searched the Medline, Embase, Scopus, SINOMED, and Cochrane databases as well as specific journals from inception to September 2021 for observational studies that evaluated the association between constipation and the risk of PD. The Newcastle-Ottawa Scale was used to evaluate the methodological quality of the included studies. Associations were summarized as odds ratios (ORs) using a random-effects model. Subgroup, meta-regression, and sensitivity analyses were performed. Results: Seventeen studies comprising 3,024,193 participants (case-control = 1,636,831; cohort = 1,387,362) were eligible for inclusion. The pooled OR for the association between constipation and PD was 2.36 (95% confidence interval: 1.93-2.88), although strong heterogeneity was observed (I-2 = 90%, p < 0.01). Subgroup and meta-regression analyses indicated that study design and disease duration were the major sources of heterogeneity. A sensitivity analysis confirmed the stability of the outcomes. In addition, the prevalence of among those with prodromal PD was 20%, whereas it was only 11% in the control group (p < 0.01). Moreover, there were no significant age-based differences in constipation between the prodromal stage of PD patients and the controls (p > 0.05). Conclusion: Constipation has a relatively high incidence in the prodromal phase of PD and is associated with an increased risk of developing PD.