Contributions of Pain Sensitivity and Colonic Motility to IBS Symptom Severity and Predominant Bowel Habits

OBJECTIVES: Irritable bowel syndrome (IBS) patients show pain hypersensitivity and hypercontractility in response to colonic or rectal distention. Aims were to determine whether predominant bowel habits and IBS symptom severity are related to pain sensitivity, colon motility, or smooth muscle tone. METHODS: One hundred twenty-nine patients classified as IBS with diarrhea (IBS-D, N = 44), IBS with constipation (IBS-C, N = 29), mixed IBS (IBS-M, N = 45), and unspecified IBS (IBS-U, N = 11) based on stool consistency, and 30 healthy controls (HC) were studied. A manometric catheter containing a 600-mL capacity plastic bag was positioned in the descending colon. Pain threshold was assessed using a barostat. Motility was assessed for 10 min with the bag minimally inflated (individual operating pressure [IOP]), 10 min at 20 mmHg above the IOP, and for 15-min recovery following bag inflation. Motility was also recorded for 30 min following an 810-kcal meal. RESULTS: Compared with HC, IBS patients had lower pain thresholds (medians 30 vs 40 mmHg, P < 0.01), but IBS subtypes were not different. IBS symptom severity was correlated with pain thresholds (rho = -0.36, P < 0.00:1). During distention, the motility index (MI) was significantly higher in IBS compared with HC (909 73 vs 563 78, P < 0.01). Average barostat bag volume at baseline was higher (muscle tone lower) in HC compared with IBS-D and IBS-M but not compared with IBS-C. The baseline MI and bag volume differed between IBS-D and IBS-C and correlated with symptoms of abdominal distention and dissatisfaction with bowel movements. Pain thresholds and MI during distention were uncorrelated. CONCLUSIONS: Pain sensitivity and colon motility are independent factors contributing to IBS symptoms. Treatment may need to address both, and to be specific to predominant bowel habit.