Increased visceral sensitivity is one of the symptoms associated with irritable bowel syndrome (IBS). Most studies evaluating visceral pain sensation in IBS patients have been conducted with patients in the fasting state, and few comparisons have been made with regard to IBS subtype (IBS with constipation [IBS-C] or IBS with diarrhea [IBS-D]). In a study conducted by Maria P. Caldarella, MD, and colleagues (American Journal of Gastroenterology, February 2005), visceral sensitivity, perceptions, and symptoms were monitored in IBS patients and controls before and after low-fat intraduodenal infusion.
IBS patients perceived rectal wall tension at significantly lower levels than did healthy patients, and the infusion of fats significantly lowered the tension threshold. Furthermore, IBS patients perceived pain during distension, whereas healthy patients did not report pain even at greater pressures. During distension, there was a qualitative difference between the symptoms reported by patients with IBS-C and those with IBS-D. Most IBS-C patients reported a cramping/colicky sensation, and those with IBS-D reported feelings of urgency and the need to evacuate. These results suggest a possible difference in the mechanism(s) for processing peripheral stimulation of the rectum in the IBS subgroups.