Di Stefano M et al. (2006) Meal induced rectosigmoid tone modification: a low caloric meal accurately separates functional and organic gastrointestinal disease patients. Gut 55: 1409–1414

There is no accurate test for a positive diagnosis of IBS, despite the high incidence of the condition; at present, arbitrary criteria are used to arrive at the diagnosis. There are two clinical patterns of IBS—constipation-predominant and diarrhea-predominant—and there have been conflicting reports as to whether altered sensation and/or motor activity in the intestine result in the alterations in motility that give rise to the symptoms associated with this condition.

Di Stefano et al., therefore, measured the postprandial rectosigmoid response of patients with and without IBS, using the rectosigmoid barostat test (they assessed 32 patients with constipation-predominant IBS, 24 patients with diarrhea-predominant IBS, 10 patients with functional diarrhea, 10 patients with functional constipation, 29 patients with organic gastrointestinal disease, and 10 healthy volunteers).

Healthy individuals and patients with organic disease had a reduced rectosigmoid volume after consuming a 200 kcal meal (compared with their fasting rectosigmoid volumes), which indicated a postprandial increase in muscle tone. By contrast, patients with diarrhea-predominant IBS had a postprandial reduction in rectosigmoid tone, and patients with constipation-predominant IBS had little or no postprandial change in muscle tone.

The authors conclude that patients with IBS have an altered gastrorectal reflex, and that the postprandial response patterns differ for patients with constipation-predominant and diarrhea-prominent IBS. They highlight the need for large trials to evaluate the use of postprandial rectosigmoid tone modification as a diagnostic test for IBS.