Small intestinal bacterial overgrowth: histopathologic features and clinical correlates in an underrecognized entity.

CONTEXT: Small intestinal bacterial overgrowth (SIBO) is a common cause of chronic diarrhea and malabsorption. Morphologic changes associated with this condition have not, to our knowledge, been studied in detail.
OBJECTIVE: To better characterize the histopathologic changes associated with SIBO by comparing the clinicopathologic features of patients with SIBO (duodenal aspirate cultures with > or =10(5) colony-forming units [CFUs]/mL) to controls with cultures found to be negative (<10(5) CFUs/mL).
DESIGN: We included 67 consecutive patients with SIBO and 55 controls in the series. Each duodenal biopsy was assessed for the following features: villous to crypt ratio, intraepithelial lymphocytosis, crypt apoptoses, basal plasmacytosis, cryptitis/villitis, peptic duodenitis, erosions/ulcers, eosinophilia, and absence of goblet and Paneth cells; and correlated with clinical features and culture results.
RESULTS: Decreased villous to crypt ratio (<3ratio1) was more frequent in SIBO than controls (24% versus 7%; P = .01). Duodenal biopsies from patients with SIBO were slightly less likely to be judged within reference range than were controls (52% versus 64%; P = .27). There were no significant differences in any of the other histologic features. Clinically, patients in the SIBO group were older than the age of controls (mean, 60 years versus 52 years; P = .02), and they were more likely to have one of the known predisposing factors for bacterial overgrowth (66% versus 36%; P = .002). Other clinical features, including presenting symptoms, were similar.
CONCLUSIONS: Villous blunting is the only feature more common to SIBO than to controls. More than half of biopsies from SIBO patients are histologically unremarkable. Therefore, SIBO needs to be considered as a potential etiology for gastrointestinal symptoms even when duodenal biopsies are found to be normal.