Incomplete microscopic colitis in Vietnam: perspectives for clinical practice

Microscopic colitis (MC) is an established cause of chronic watery diarrhea in Western countries but remains underrecognized in Asia. Incomplete forms, such as incomplete collagenous colitis (iCC), pose additional diagnostic challenges as they exhibit borderline histological changes and are often mislabeled as “nonspecific colitis” or overlooked entirely. iCC was defined by accepted histological criteria as a subepithelial collagen band of 5–10 μm and/or borderline intraepithelial lymphocyte (IEL) counts of 10–20 per 100 surface epithelial cells. No case of iCC has previously been documented in Vietnam. We report a 60-year-old woman who presented with persistent watery diarrhea and was initially diagnosed with diarrhea-predominant irritable bowel syndrome (IBS-D). Despite a macroscopically normal colonoscopy, segmental biopsies were obtained. Histology with Masson’s trichrome revealed a 7-µm subepithelial collagen band, while CD3 immunohistochemistry demonstrated 6–7 intraepithelial lymphocytes per 100 epithelial cells, consistent with iCC. Because budesonide was unavailable, loperamide 4 mg/day was prescribed, leading to rapid improvement and sustained symptom control over six months. We reviewed Asian and selected Western studies on MC and its incomplete variants. Most Asian cohorts did not disaggregate incomplete phenotypes, terminology was inconsistent, and staining practices varied. Systematic biopsies were rarely performed in patients with normal colonoscopy, contributing to the apparently low incidence of MC in Asia. This first Vietnamese case of iCC, together with systematic review findings, highlights diagnostic gaps rooted in biopsy practices, staining availability, and terminology. Adoption of a biopsy-first reflex in chronic watery diarrhea, use of minimal stain bundles, and regionally calibrated criteria are essential to uncover the true burden of MC in Asia and improve patient outcomes.