Table 3.

Histopathological criteria for MC according to the UEG and EMCG guidelines.

MC Features	CC	LC	MCi
Characteristic feature	Thickening of the collagen band > 10 μm, which may be irregularly thicker at the periphery (vertical positioning of the biopsy is recommended to better visualise the collagen band)	>20 IEL per 100 epithelial cells (IHC staining is recommended to facilitate counting)	CCi: thickening of subepithelial collagen band > 5 μm but less than 10 μm LCi: >10 IEL but less than 20 IEL per 100 epithelial cells and normal collagen band
Damage to the surface epithelium	Focal detachment from basement membrane, flattening, less mucus	Flattening, reduced mucin, and vacuolisation (less well expressed than in CC)
Inflammatory plaque infiltration	Composed of plasma cells, lymphocytes, eosinophils, mast cells, and neutrophils	Predominance of lymphocytes and plasma cells; eosinophils and neutrophils sometimes present
Paneth cell metaplasia	Rarely	Rarely
Inflammation of the crypts	Rarely	Rarely

CC—collagenous colitis, CCi—incomplete collagenous colitis, IEL—intraepithelial lymphocyte, IHC—immunohistochemistry, LC—lymphocytic colitis, LCi—incomplete lymphocytic colitis, and MCi—incomplete microscopic colitis.