A recent study in the medical journal, BMC Gastroenterology, has confirmed an increased incidence of other conditions occurring with IBS, specifically migraine, depression, and fibromyalgia. Some physicians class these conditions together as ‘affective spectrum disorders,’ or ‘functional somatic syndromes’. While clinicians have been reporting the connection between IBS and these conditions for about fifteen years, this new study shows a high degree of correlation in their relationships to IBS, within a large population base.

The hypothesis developed from observations that people treated with antidepressant therapy for migraine, fibromyalgia, and depression responded favourably, presumably since tricyclic antidepressants affect pain thresholds. Since the same medication helps all three disorders, the logical extension of this thinking led to the speculation that they may have the same underlying biological mechanism.

A number of past studies have examined and documented the relationship between IBS and these other conditions. In a study looking at those with fibromyalgia, 39% had IBS, 45% had migraine, and 42% had chronic fatigue syndrome. Another study showed a familial association among patients with major depressive disorder and fibromyalgia, IBS, and migraine. A more recent Canadian study, proposed that a single diagnostic entity could replace the separate diagnostic criteria used to define fibromyalgia, IBS, depression, and chronic fatigue syndrome. In 1999, 32% of people with IBS in one study also had symptoms of fibromyalgia, compared with only 4% of individuals without IBS. Far-ranging data on the prevalence of depression in conjunction with IBS have ranged from a study showing absolutely no association, to one that revealed up to a 94% co-morbidity of depression, anxiety, and somatoform disorders in people with IBS.

Despite the above data, there remained gaps in the scientific evidence linking IBS with migraine, depression, and fibromyalgia. This newest study sought to address these gaps by looking at a very large cohort of study participants and comparing those with and without IBS. Using strict design criteria, researchers identified incidences of each of the three linked conditions. They pulled data from medical and pharmacy claims to a large US national health insurer, selecting a total cohort of almost 125,000 patients seen for either IBS (97,593; 75% female) or for routine medical care (27,402; 50% female), who became the non-IBS group. Compared with the non-IBS group, those with IBS were 60% more likely to have any one of the three disorders identified. Although, the researchers did not have details regarding any IBS sub-group, such as IBS Alternating, Constipation, or Diarrhea, these sub-types are generally fairly evenly distributed throughout the IBS population.

People in the IBS cohort had 40% to 80% higher prevalence odds for migraine, fibromyalgia, and depression in comparison to the non-IBS cohort. The authors conclude that their current findings support previous reports, which have promoted speculation that all four disorders share an underlying biological mechanism. Further research might provide more clarification on their true biological relationships.

First published in the Inside Tract® newsletter issue 159 – January/February 2007
BMC Gastroenterology 2006, 6:26