In a study released at the Annual Scientific Meeting of the American College of Gastroenterology, researchers from the Alimentary Pharmabiotic Centre at University College Cork suggest that psychological factors such as anxiety and depression may be central drivers of inflammatory changes in IBS rather than inflammation originating in the gut itself.

In the study, "Circulating Cytokines in IBS Subgroups," researchers from the Alimentary Pharmabiotic Centre at University College Cork aimed to determine whether circulating cytokine levels are associated with distinct IBS subgroups.

"The main finding, which confirms several prior studies from our group, is the elevated level of the cytokine interleukin-6 (IL-6), a pro-inflammatory cytokine, in the blood in those with IBS," said Eamonn M.M. Quigley, M.D., FACG, lead author who is now head of Gastroenterology at Houston Methodist Hospital.  "For the first time, we showed that this is a constant finding over time."

Dr. Quigley and his team looked at a whole range of demographic factors that could be related to IL-6 levels and, in particular, to the IBS subgroups that have been so widely studied before and defined according to dominant stool pattern: diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), and alternating constipation-diarrhea (IBS-M).

According to the results, higher levels of plasma IL-6 are associated with the presence of psychological comorbidity in those with IBS. This suggests that disturbances in circulating cytokines may be centrally mediated rather than reflecting inflammation at the mucosal level.

"While these are relatively low levels and rather subtle changes, their relationship to anxiety and depression is interesting as these disorders, per se, have been linked to increased inflammatory tone," said Dr. Quigley. "The results also suggest that variability in the levels of these cytokines is linked to symptom severity as well as levels of anxiety and depression. When one sees elevated levels of inflammatory markers in any intestinal disorder the immediate assumption is that it originates from an inflammatory process in the intestine itself. But our results suggest that it may be central factors like anxiety and depression that are actually the drivers and it has been shown in other contexts that this, indeed, can happen."

With IBS sometimes challenging to treat and manage, the results of this study raise two issues, according to Dr. Quigley. "Can we use this as a test to differentiate those IBS subjects for whom central factors, like anxiety and depression, may be more important; and will centrally-directed therapies (antidepressants and anti-anxiety drugs) be more effective in this group?"

"The relationship between inflammatory cytokines with anxious and depressed mood is well recognized within psychiatry," commented Dr. Drossman, who is Adjunct Professor of Medicine and Psychiatry at the University of North Carolina. "Dr. Quigley's group has confirmed that in a cohort of patients with IBS this association of mood with cytokine activation exists more so than in healthy controls who were presumably psychologically healthy."