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

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.

The goal was to characterize IMO prevalence in PD and compare findings with constipation reference groups.

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.

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).

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.