Clinical Characteristics and Treatment Outcomes in Patients With Incomplete Microscopic Colitis: Consideration for Expanding the Definition of Microscopic Colitis.

BACKGROUND & AIMS: Incomplete microscopic colitis (MCi) is inadequately characterized and does not meet the histologic criteria for microscopic colitis (MC). The clinical features, treatment outcomes, and rates of recurrence are not well-known. The objective of this study was to assess these features.

METHODS

Adults with chronic watery diarrhea diagnosed with MCi on histology (2010-2023) at Mayo Clinic were identified. Response at 12 ± 4 weeks after treatment initiation was defined as: complete (resolution of diarrhea), partial (≥50% improvement), nonresponse (<50% improvement), or intolerance (withdrawal due to adverse effects). Logistic and Cox regression were used to identify predictors of nonresponse and risk of recurrence.

RESULTS

A total of 204 patients were identified (median age, 62 years [range, 22-90 years]; 66.2% women) with median follow-up of 3.1 years (range, 0.4-13.3) years. Most (80.4%) were on drugs commonly implicated in MC; 6.8% had improvement after discontinuation of associated culprit medications alone. Patients were treated with the following: 37.3% loperamide, 28.4% budesonide, 18.6% bismuth subsalicylate, 7.4% bile acid sequestrant, and 1.5% other medications. Clinical outcomes were: 72.6% complete response, 22.1% partial response, 3.4% nonresponse, and 1.9.% intolerance. There were no differences in outcomes between MCi subtypes (P = .11). Fecal incontinence was the only predictor of nonresponse. After discontinuation of therapy, 35.8% had recurrence, and 13.7% developed MC.

CONCLUSIONS

In one of the largest cohorts of MCi, the majority were on drugs implicated in MC and almost three-fourths had a complete response to therapy including budesonide. Given the commonalities with MC, the histologic definition should potentially be expanded to include these patients.