Increased visceral sensitivity is one of the symptoms associatedwith irritable bowel syndrome (IBS). Most studies evaluatingvisceral pain sensation in IBS patients have been conductedwith patients in the fasting state, and few comparisons havebeen made with regard to IBS subtype (IBS with constipation[IBS-C] or IBS with diarrhea [IBS-D]). In a study conducted byMaria P. Caldarella, MD, and colleagues (American Journal ofGastroenterology, February 2005), visceral sensitivity, perceptions,and symptoms were monitored in IBS patients and controlsbefore and after low-fat intraduodenal infusion.
IBS patients perceived rectal wall tension at significantly lowerlevels than did healthy patients, and the infusion of fats significantlylowered the tension threshold. Furthermore, IBS patientsperceived pain during distension, whereas healthy patients did notreport pain even at greater pressures. During distension, therewas a qualitative difference between the symptoms reported bypatients with IBS-C and those with IBS-D. Most IBS-C patientsreported a cramping/colicky sensation, and those with IBS-Dreported feelings of urgency and the need to evacuate. Theseresults suggest a possible difference in the mechanism(s) for processingperipheral stimulation of the rectum in the IBS subgroups.