Aims Mycophenolate-associated colitis has been previously reported to show patterns of colonic mucosal injury mimicking a host of conditions, including graft-versus-host disease, ischaemia and inflammatory bowel disease (IBD). The aim of this study is to characterise, semiquantitatively, pathological changes of mycophenolate mofetil (MMF) mucosal injury.

Methods Seven transplant patients receiving MMF who underwent colonoscopic examination and biopsy were identified retrospectively over a 2-year period. Multiple histologic parameters, including architectural distortion, cryptitis, stromal active inflammation, individual damaged crypts (IDC) and crypt apoptotic figures were evaluated in the biopsies semiquantitatively. Where biopsy site was identified, the parameters were assessed separately in biopsies from right and left colon.

Results All cases showed mixed patterns of mucosal injury. All seven cases showed focal architectural distortion (in 58% of fragments per case), focal cryptitis (mean 3.0 foci per case), increased crypt apoptosis (mean 26.5/100 crypts) and IDC (mean 3.0 foci). Focal changes resembling acute self-limited colitis were noted in three cases. Possible proximal accentuation of some changes was noted with right side biopsies tending to show greater crypt apoptotic activity and more foci of architectural distortion. Three cases showed dual pathology (two with cytomegalovirus (CMV) infection and one with IBD).

Conclusions Although a wide spectrum of changes may be seen in MMF-associated colitis, important microscopic clues include a mixed pattern of injury (typically a combination of crypt apoptosis, isolated crypt damage and architectural distortion), and possible proximal accentuation of pathologic changes. The need for clinical correlation and follow-up is emphasised by the occurrence of dual pathology in patients treated with MMF.