Atypical forms of inflammatory bowel disease

Interaction of gut microbiota with bile acid metabolism and its influence on disease states

Primary bile acids serve important roles in cholesterol metabolism, lipid digestion, host-microbe interactions, and regulatory pathways in the human host. While most bile acids are reabsorbed and recycled via enterohepatic cycling, ∼5% serve as substrates for bacterial biotransformation in the colon. Enzymes involved in various transformations have been characterized from cultured gut bacteria and reveal taxa-specific distribution. More recently, bioinformatic approaches have revealed greater diversity in isoforms of these enzymes, and the microbial species in which they are found. Thus, the functional roles played by the bile acid-transforming gut microbiota and the distribution of resulting secondary bile acids, in the bile acid pool, may be profoundly affected by microbial community structure and function. Bile acids and the composition of the bile acid pool have historically been hypothesized to be associated with several disease states, including recurrent Clostridium difficile infection, inflammatory bowel diseases, metabolic syndrome, and several cancers. Recently, however, emphasis has been placed on how microbial communities in the dysbiotic gut may alter the bile acid pool to potentially cause or mitigate disease onset. This review highlights the current understanding of the interactions between the gut microbial community, bile acid biotransformation, and disease states, and addresses future directions to better understand these complex associations.

Ischaemia: a pathogenetic clue in diversion colitis?

OBJECTIVE

It is not common that, after diversion of the faecal stream by a colostomy, the defunctioned colon develops colitis. The pathogenesis of this colitis is still unclear and it has been proposed that ischaemia may play a major role. Our aim is to look for signs of ischaemia in a group of patients developing colitis after diversion colostomy for various causes.

METHOD

Surgical specimens from 32 patients resected for colitis developed after diverting colostomy were examined with routine (haematoxylin-eosin) and Elastic-Van Gieson and Perls' stains.

RESULTS

The histological features related to mucosal crypt architecture, crypt epithelium and inflammation were mild, non specific or related to the underlying disease. Fibrosis was present in 21 (65.6%) patients, superficial coagulative necrosis was found in 18 (56%) patients, splitting and/or thickening of muscularis mucosae was present in 20 (62%) patients. The vessels were substantially normal or ectasic without thrombi or alterations in the wall. Evident ischaemia with coagulative necrosis, submucosal oedema and focal fibrosis was detected in only two (6%) patients and an intermediate picture between acute and chronic ischaemia was present in 16 (50%) patients.

CONCLUSION

It is possible that ischaemia plays some role in the pathogenesis of diversion colitis; however, further studies are needed to firmly establish its role.

Audit of the histopathological diagnosis of non-neoplastic colorectal biopsies: achievable standards for the diagnosis of inflammatory bowel disease

AIM

To assess the performance of a histopathology department in diagnosing inflammatory bowel diseases with comparison of reports from other centres.

STUDY POPULATION

1067 sets of endoscopic biopsies received in the department of histopathology, Royal Hallamshire Hospital, 1990-1995.

METHODS

The histopathological diagnosis of non-neoplastic endoscopic colorectal biopsies was audited using data from histopathology reports. The biopsy diagnosis by the initial reporting pathologist and final diagnosis after additional investigations (endoscopy, radiology, microbiology) or surgery were used to derive sensitivity, specificity, and positive predictive values for categories of disease.

RESULTS

Diagnosis was validated for 1067 biopsy sets (43% of those initially assessed). For all biopsies (with or without active inflammation) reports highly suggestive or suggestive of Crohn's disease had a sensitivity of 50%; for ulcerative colitis the comparable figure was 62%. Sensitivity was the same for both diagnoses (74%) in those biopsies with active inflammation. Positive predictive values for highly suggestive diagnoses of ulcerative colitis or Crohn's disease were 100%. In all biopsies the specificity of a histopathological diagnosis of normality was 96%.

CONCLUSIONS

These results compare favourably with the other published audits and present an achievable level of performance for non-specialist hospitals with non-specialist histopathology services.