Safety and efficacy of faecal microbiota transplantation in Parkinson's disease.

The gut microbiota may influence Parkinson's disease's (PD) pathophysiology. Faecal Microbiota Transplantation (FMT) may therefore improve symptoms. We reviewed five randomized controlled trials (RCT), three cohort studies, one case series, and two single case reports (total of 236 subjects). FMT methods varied (donor selection, FMT preparation method, pre-treatment, administration). Mild, self-limiting gastrointestinal symptoms were the most common adverse events (AEs). Constipation improved consistently after FMT. Motor and non-motor outcomes were heterogeneous, with improvements mainly reported in uncontrolled studies. One RCT demonstrated motor improvement at 8-12 weeks, another only after one year, while others showed no significant changes. In most RCTs, changes fell within or just beyond the minimal clinically important differences (MCID). Five studies reported taxonomic shifts, most consistently increased within the phylum Firmicutes. Large, well-designed RCTs with optimized FMT protocol for patient selection, FMT preparation and delivery, and donor selection are needed to determine whether FMT can affect PD symptoms or disease progression.