In Regard to Harris et al

Abstract

To the Editor: We would like to congratulate Harris et al ( 1 Harris V. Benton B. Sohaib A. et al. Bile acid malabsorption after pelvic and prostate intensity modulated radiation therapy: an uncommon but treatable condition. Int J Radiat Oncol Biol Phys. 2012; 84: e601-e606 Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar ) for their recent publication. The authors have done an interesting research in studying bile acid malabsorption (BAM) caused by radiation delivered to the terminal ileum during intensity modulated radiation therapy and highlighting the need and advantages of expert gastrointestinal assessment of symptoms after pelvic irradiation. Certain issues in the study need consideration. It is important to rule out other causes of BAM. Three types of BAM are proposed: type 1, resulting from severe disease, resection, or bypass of the distal ileum; type 2, or primary BAM; and type 3, in which BAM follows upper abdominal surgery, either truncal vagotomy or cholecystectomy, celiac disease, or pancreatic insufficiency ( 2 Williams A.J.K. Merrick M.V. Eastwood M.A. Idiopathic bile acid malabsorption: a review of clinical presentation, diagnosis, and response to treatment. Gut. 1991; 32: 1004-1006 Crossref PubMed Scopus (124) Google Scholar ). Lower gastrointestinal endoscopy should have been undertaken to look for radiation-induced structural changes and confirm that BAM is secondary to radiation therapy. The selenium homocholic acid taurine (SeHCAT) test should be used cautiously in patients with liver diseases as these may interfere with the results. Moreover, the presence of bacterial overgrowth in the small bowel may also influence the interpretation of the SeHCAT test result ( 3 Pattni S. Walters J.R. Recent advances in the understanding of bile acid malabsorption. Br Med Bull. 2009; 92: 79-93 Crossref PubMed Scopus (83) Google Scholar ). The combination of bile acid breath test and SeHCAT together with the 14C-xylose breath test is useful in evaluating chronic diarrhea after radiation therapy because both bile acid malabsorption and bacterial contamination by anaerobic and aerobic bacteria can be detected ( 4 Danielsson A. Nyhlin H. Persson H. et al. Chronic diarrhoea after radiotherapy for gynaecological cancer: occurrence and aetiology. Gut. 1991; 32: 1180-1187 Crossref PubMed Scopus (79) Google Scholar ). It is also important to know what fraction of total patients experienced diarrhea in the present cohort, because it can be a manifestation of radiation therapy without BAM. Although the SeHCAT test is very specific, it is not without limitations. The normal values for bile acid retention, which are used to compare normal and abnormal bile acid malabsorption, were obtained only in healthy persons without diarrhea ( 5 Sciarretta G. Vicini G. Fagioli G. et al. Use of 23-selena-25-homocholyltaurine to detect bile acid malabsorption in patients with illeal dysfunction or diarrhea. Gastroenterology. 1986; 91: 1-9 PubMed Google Scholar ). Also, secondary bile acid malabsorption can be induced by diarrhea itself and is proportional to the stool weight, so it should have been demonstrated with a carbon-14-taurocholate bile acid absorption test ( 6 Schiller L.R. Hogan R.B. Morawski S.G. et al. Studies of the prevalence and significance of radiolabeled bile acid malabsorption in a group of patients with idiopathic chronic diarrhea. Gastroenterology. 1987; 92: 151-160 PubMed Google Scholar , 7 Guirl M.J. Högenauer C. Santa Ana C.A. et al. Rapid intestinal transit as a primary cause of severe chronic diarrhea in patients with amyloidosis. Am J Gastroenterol. 2003; 98: 2219-2225 Crossref PubMed Scopus (42) Google Scholar ). The study would have been more interesting if the doses to terminal ileum in patients having diarrhea without BAM had also been commented on to obtain a dose-response relationship curve, because it may have established the relationship of dose and volume of the irradiated terminal ileum to complications. In view of the lack of oral contrast medium and the difficulty in identifying and contouring the terminal ileum, the doses to the terminal ileum could have been underestimated. Bile Acid Malabsorption After Pelvic and Prostate Intensity Modulated Radiation Therapy: An Uncommon but Treatable ConditionInternational Journal of Radiation Oncology, Biology, PhysicsVol. 84Issue 5PreviewIntensity modulated radiation therapy (IMRT) is a significant therapeutic advance in prostate cancer, allowing increased tumor dose delivery and increased sparing of normal tissues. IMRT planning uses strict dose constraints to nearby organs to limit toxicity. Bile acid malabsorption (BAM) is a treatable disorder of the terminal ileum (TI) that presents with symptoms similar to radiation therapy toxicity. It has not been described in patients receiving RT for prostate cancer in the contemporary era. Full-Text PDF