Lessons for inflammatory bowel disease from rheumatology.

There are several areas of overlap between gastroenterology and rheumatology, some related to the side effects of drugs but others related to the similarities in probable pathogenic mechanisms and treatments. This is best illustrated by comparison between inflammatory bowel disease and rheumatoid arthritis-conditions of uncertain aetiology that are due to a combination of genetic and environmental factors and are associated with chronic inflammation in the absence of any clearly recognisable pathogen. Medical research is increasingly specialised but careful comparison of the relevant gastroenterological and rheumatological literatures suggests several common areas that are worthy of greater attention than they are currently receiving. These could include studies to address the following questions: (1) What are the functional and antigen-binding differences of the HLA class II alleles that are differently associated with rheumatoid arthritis and ulcerative colitis? (2) Why are both Crohn's disease and rheumatoid arthritis associated with smoking, yet, with one condition (Crohn's disease) increasing recently in incidence and the other (rheumatoid arthritis) becoming less common? (3) Which genetic and/or environmental factors distinguish the Turkish patients with HLA-B51-associated Behcet's disease who tend not to develop colitis and the Japanese patients with HLA-B51-associated Behcet's disease who develop colitis? (4) Is pANCA directly involved in the pathogenesis of ulcerative colitis-given evidence of its direct involvement in the pathogenesis of vasculitis? (5) Given the arguably greater similarity between rheumatoid arthritis and ulcerative colitis than with Crohn's disease, is etanercept effective in ulcerative colitis? (6) Do the very different risks of cancer in chronically inflamed colon and inflamed joints imply that cancer development requires both NFkappaB activation, to inhibit apoptosis, and the presence of agents, such as bacteria, to initiate DNA damage?