Prevalence of Intestinal Methanogen Overgrowth in Progressive Supranuclear Palsy: A Case-Control Study

Objective　Progressive supranuclear palsy (PSP) is a rare neurodegenerative disorder frequently accompanied by severe gastrointestinal dysfunction, particularly constipation. Although small intestinal bacterial overgrowth (SIBO) has been reported in several neurological diseases, intestinal microbial phenotypes in patients with PSP have not been systematically evaluated. This study aimed to assess the prevalence of intestinal methanogen overgrowth (IMO) and hydrogen-type SIBO in patients with PSP.Methods　We conducted a cross-sectional case-control study to evaluate hydrogen- and methane-based breath test profiles in patients with PSP. Breath testing was performed in accordance with the North American Consensus criteria. The prevalence of hydrogen-type SIBO and IMO was compared between patients with PSP and healthy controls.Results　Five patients with PSP and 33 healthy controls were included. IMO was identified more frequently in patients with PSP than in healthy controls (40.0% vs. 3.0%; P = 0.040). In contrast, hydrogen-type SIBO was not observed in either group. The mean Gastrointestinal Symptom Rating Scale (GSRS) score among patients with PSP was 29.4±5.9, and no clear association was observed between IMO positivity and gastrointestinal symptom severity or the presence of constipation.Conclusions　Patients with PSP exhibited a distinct intestinal microbial phenotype characterized by methanogen predominance rather than hydrogen-type SIBO. Although limited by the small sample size, this pilot study provides novel insights into the gut microbial characteristics of PSP and suggests that qualitative alterations in the small intestinal microbiota and motility may contribute to PSP-associated gastrointestinal dysfunction.