Sustained normalization of hydrogen-positive small intestinal bacterial overgrowth after polyethylene glycol bowel preparation.

Small intestinal bacterial overgrowth (SIBO) is a frequent complication of chronic liver disease with portal hypertension that often persists or recurs despite standard treatments. Polyethylene glycol (PEG)-based bowel preparations are routinely used before colonoscopy; however, their effects on SIBO have not yet been systematically evaluated. We report the case of a 44-year-old man with metabolic dysfunction-associated steatohepatitis, complicated by intrahepatic portal vein thrombosis and esophagogastric varices. Before colonoscopy, hydrogen and methane breath testing revealed hydrogen-positive and methane-negative SIBO, while the gastrointestinal symptoms were mild, with a Gastrointestinal Symptom Rating Scale score of 15. Subsequently, the patient underwent a standard bowel preparation using a PEG electrolyte solution. No antibiotics, probiotics, laxatives, or dietary interventions were administered before or after the procedure. Follow-up breath tests performed 1 week after bowel preparation demonstrated normalization of both hydrogen and methane levels. Importantly, repeat testing at 6 weeks confirmed sustained negativity without any additional interventions. This case highlights a previously unreported phenomenon, suggesting that transient luminal interventions, such as bowel preparation, may influence small intestinal microbial dynamics in selected high-risk patients. This observation should be considered hypothesis-generating, and no conclusions regarding therapeutic efficacy can be drawn from this single case.