Response to: Kittisupamongkol W (2009) Depth of inflammation in Crohn's disease. Nat Clin Pract Nephrol [doi:10.1038/ncpneph1044]

Original article: Waters AM et al. (2008) Tubulointerstitial nephritis as an extraintestinal manifestation of Crohn's disease. Nat Clin Pract Nephrol 4: 693–697 [doi:10.1038/ncpneph0955]

Technically, the reader is correct, that Crohn's disease is differentiated from ulcerative colitis by the depth of inflammation on surgical specimens of resected bowel: ulcerative colitis is limited to the mucosa and Crohn's disease can be deeper or transmural. Endoscopically, of course, we can only appreciate mucosal ulcerations, and endoscopic biopsies are only mucosal. Perhaps we could have modified the opening line of the discussion to something simpler such as “Crohn's disease is a chronic relapsing inflammatory disease of the gastrointestinal tract.” And maybe we could have expanded this section regarding the nature of the inflammation. We didn't think this was necessary, however, as our case met diagnostic criteria. We hope this response helps, a little.