The histopathology of ‘microscopic colitis’: Classical and non-classical forms

Microscopic colitis is an inflammatory condition of the large bowel that is distinct from inflammatory bowel disease and infection. Several histological patterns of inflammation have been described. The classification of microscopic colitis needs to evolve to take into account newly described patterns. We suggest an approach to analysing biopsies in cases of suspected microscopic colitis and propose a new classification system. We divide microscopic colitis into classical (collagenous colitis, lymphocytic colitis) and non-classical (granulomatous colitis, giant-cell microscopic colitis, pseudomembranous microscopic colitis). We also propose that minimal-change colitis should not be considered under the heading of microscopic colitis.