SATB2 and Hep Par 1 Immunohistochemistry Is Helpful in Distinguishing Between Inflamed and Architecturally Altered Ileal Pouch and Rectal Cuff Mucosa

The management of patients with ulcerative colitis after proctocolectomy with ileal pouch-anal anastomosis includes independent histological assessments of inflammation in the ileal pouch and the rectal cuff. However, the distinction between pouchitis and cuffitis can be impeded both endoscopically and histologically by the combined effects of inflammation and regeneration. We investigated the use of 2 markers, hepatocyte paraffin 1 (Hep) and SATB2 (special AT-rich sequence-binding protein 2), which are expressed immunohistochemically in the small and large bowel epithelium, respectively, as ancillary methods to deal with this problem. Immunohistochemical staining was performed retrospectively on 20 consecutive pairs of post–ileal pouch-anal anastomosis biopsies with varying degrees of histological inflammation and architectural distortion, which had each been designated as “ileal pouch” or “rectal cuff” by the referring endoscopists. Expression was graded as focal (10% to 74% stained cells) or diffuse (75% to 100%). Among the ileal pouch biopsies, 20 (100%) expressed Hep either diffusely (75%) or focally (25%), whereas SATB2 staining was either negative in 15 (75%) or focal in 5 (25%), the latter group all expressing Hep diffusely. Among the rectal cuff biopsies, 14 expressed SATB2 diffusely. Of these, Hep was either negative in 11 (79%) or focally positive in 3 (21%), the latter group all expressing SATB2 diffusely. Six ostensibly rectal cuff biopsies (30%) expressed Hep diffusely and were negative for SATB2, suggesting endoscopic misidentification. None of the 40 biopsies expressed both markers diffusely. We conclude that in doubtful cases, diffuse expression of either Hep or SATB2 can be helpful in discriminating between ileal pouch and rectal cuff mucosa, respectively.