Fecal Microbiota Transplantation in Parkinson Disease: A Systematic Review, Meta-Analysis, and Meta-Regression

Parkinson disease (PD) is a progressive neurodegenerative disorder increasingly linked to gut microbiota dysbiosis, which may influence disease mechanisms and symptom expression. Fecal microbiota transplantation (FMT) targets the gut-brain axis, but clinical evidence remains inconsistent. This study aimed to evaluate the efficacy and safety of FMT in PD.

We conducted a systematic review and meta-analysis following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, with protocol registration in International Prospective Register of Systematic Reviews (CRD420251142846). MEDLINE, Embase, and the Cochrane Library were searched from inception through September 2025. Randomized controlled trials (RCTs) and observational studies enrolling adults with mild-to-moderate PD who received FMT through any administration route were eligible. The primary outcome was motor function assessed by the Unified Parkinson's Disease Rating Scale (UPDRS) part III. Secondary outcomes included UPDRS part II, quality of life (Parkinson's Disease Questionnaire-39 [PDQ-39]), constipation severity (Wexner score), and adverse events. Random-effects models pooled effect estimates with 95% CIs, and exploratory meta-regression assessed follow-up duration, publication year, and sample size.

Eight studies (5 RCTs and 3 observational studies) including 220 participants were analyzed. The mean age ranged from approximately 60 to 70 years, and women comprised about 40% of participants. FMT was associated with significant improvement in motor function (UPDRS part III: mean difference [MD] -9.67, 95% CI -16.81 to -2.53) and constipation severity (Wexner score: MD -3.91, 95% CI -7.68 to -0.13). Improvements in UPDRS part II and PDQ-39 were observed at 12 weeks but not sustained at 24 weeks. In RCT-only analyses, UPDRS part III improvement remained significant (MD -6.82, 95% CI -11.23 to -2.40), whereas other outcomes were not consistently significant. Meta-regression indicated that longer follow-up was associated with greater improvement in UPDRS part II (p = 0.043). FMT was generally well tolerated; however, gastrointestinal adverse events were more frequent in the FMT group (risk ratio 3.12, 95% CI 1.14-8.53), predominantly mild to moderate.

FMT may provide short-term improvements in motor and gastrointestinal symptoms in PD, but effects appear transient. Small sample sizes, heterogeneity, and limited follow-up restrict conclusions, underscoring the need for larger randomized trials. Pooled estimates reflected evidence from observational studies and should be interpreted cautiously.