Intestinal Methanogen Overgrowth in Parkinson's Disease Reflects Constipation Physiology: A Matched Cohort Study

BACKGROUND: Intestinal methanogen overgrowth (IMO) is associated with delayed intestinal transit. Chronic constipation and slow colonic transit are common in Parkinson's disease (PD) and may favor methanogen overgrowth. OBJECTIVES: The goal was to characterize IMO prevalence in PD and compare findings with constipation reference groups. METHODS: We retrospectively studied patients with PD who underwent hydrogen-methane breath testing at a tertiary center. IMO was defined as peak methane ≥10 ppm. Patients were matched 1:2 to constipation-spectrum comparators by age, sex, body mass index, test substrate, and irritable bowel syndrome status. A separate constipation cohort with objective colonic transit data provided sensitivity comparisons. RESULTS: Among 93 patients with PD, IMO was present in 46.2% and small intestinal bacterial overgrowth (SIBO) in 15.1%. Isolated IMO occurred in 36.6% and IMO + SIBO in 9.7%. IMO prevalence did not differ by substrate, time relative to PD diagnosis or Movement Disorder Society Unified Parkinson's Disease Rating Scale part III motor score (all P > 0.05). IMO prevalence was comparable between PD and the matched chronic constipation population (42.1% vs. 44.7%; P = 0.703) with similar methane burden. Specifically, IMO prevalence in PD was comparable to that in slow-transit constipation (46% vs. 48%), but significantly higher than in normal-transit constipation (46% vs. 29%; adjusted P = 0.038). CONCLUSIONS: In this first characterization of IMO in PD, nearly half of patients tested met criteria for IMO-a prevalence comparable to slow-transit constipation and independent of motor severity or disease duration. Prospective studies should determine whether constipation-directed treatment alone or with methanogen-directed therapy improves outcomes in this population.