Thicker Posterior Insula Is Associated With Disease Duration in Women With Irritable Bowel Syndrome (IBS) Whereas Thicker Orbitofrontal Cortex Predicts Reduced Pain Inhibition in Both IBS Patients and Controls

Patientswithirritablebowelsyndrome(IBS)areaffectedbychronicabdominalpainandshow decreasedpaininhibition.Moreover,theyexhibitdifferencesinbrainmorphologycomparedwithhealthy volunteers. The aim of this study was to examine whether decreased pain inhibition is associated with altered brain morphology in IBS patients. Structural magnetic resonance imaging scans were acquired in 14 female patients with diarrhea-predominant IBS and 14 controls. Pain and anxiety modulation were characterized using electrical stimulation of the sural nerve and heterotopic noxious counterstimulation. IBSpatientsreporteddecreasedpaininhibition(P=.02)aswellasincreasedshockanxiety,paincatastroph- izing,depressivesymptoms,andtraitanxiety(P's #.05). IBS patients alsoshowed a thicker right posterior insula (pINS), associated with longer IBS duration (r = .67, P = .02). In addition, thicker right lateral orbito- frontal cortex was strongly associated with less pain inhibition in both IBS patients (r = .70, P =. 02) and controls (r = .68, P = .01). Results are consistent with the role of the insula in interoception and pain and suggest that IBS may induce thickening of the pINS. Reduced pain inhibition may further involve a modi- fication of the regulatory influence of the orbitofrontal cortex on pain-related processes. Perspective: This study investigated the brain morphology of IBS patients. IBS patients showed thicker right pINS, associated with longer disease duration but not with psychological symptoms. This suggests that IBS induces thickening ofpINS, which may contribute toits pathophysiology, consis- tent with the role of the pINS in interoception and pain.