The mechanism of diarrhoea resulting from pelvic and abdominal radiotherapy; a prospective study using selenium-75 labelled conjugated bile acid and cobalt-58 labelled cyanocobalamin.

An attempt was made to elucidate the mechanism of diarrhoea resulting from pelvic and abdominal radiotherapy in a prospective study of 10 patients undergoing treatment for curable pelvic malignant tumours using the synthetic trihydroxy 75Se-labelled conjugated bile acid, SeHcat and 58Co-labelled cyanocobalamin (58Co Vit B12). Evidence of malabsorption of vitamin B12 measured as a significant fall in whole body percentage retention of 58Co Vit B12 from baseline levels was found in all nine patients who developed diarrhoea during radiotherapy. Only four out of these nine patients also had malabsorption of the trihydroxy conjugated bile acid, cholic acid, measured as a significant fall in SeHcat whole body percentage retention and these patients had the most severe diarrhoea. The findings are discussed in the light of what is known about the pathophysiology of diarrhoea during pelvic and abdominal radiotherapy and lend support to previous work which implicated increased bowel motility in the pathogenesis of radiation-induced diarrhoea. The hypothesis that local neuroendocrine mechanisms in the gut may be involved is put forward, with possible implications for treatment.