Edometriosis Linked to Later Inflammatory Bowel Disease
Ricki Lewis, PhD
December 20, 2011 — Endometriosis is associated with an increased risk of developing inflammatory bowel disease (IBD), according to a large-scale, long-term study by Danish researchers published online December 19 in Gut.
Both endometriosis and IBD present with abdominal pain, typically begin in early adulthood, and are chronic inflammatory disorders. In the past, diagnosis of one has precluded diagnosis of the other. However, Tine Jess, MD, and colleagues from the Statens Serum Institute in Copenhagen, Denmark, examined national registers to investigate the possibility that instead of being mutually exclusive, perhaps endometriosis predisposes a woman to developing IBD.
The researchers examined the medical histories of 37,661 women hospitalized for endometriosis at any time between 1977 and 2007. Of these women, 320 developed IBD (228 women developed ulcerative colitis, 92 developed Crohn's disease). The women with endometriosis had an increased risk for IBD overall (standardized incidence ratio [SIR], 1.5; 95% confidence interval [CI], 1.4 - 1.7), as well as for ulcerative colitis (SIR, 1.5; 95% CI, 1.3 - 2.0), compared with women in the general population. Stratifying the patient groups by those who underwent surgery that verified the endometriosis led to an increase in IBD risk of 80% (ulcerative colitis: SIR, 1.8 [95% CI, 1.4 - 2.3]; Crohn's disease: SIR, 1.7 [95% CI, 1.2 - 2.5]).
The increased risk persisted for 2 decades after diagnosis of IBD, and the average lag between endometriosis diagnosis and development of IBD was approximately 10 years. The fact that the association persists argues for its strength.
The researchers hypothesize 2 explanations for the association between the 2 disorders: that they share a common underlying inflammatory problem, or that treatment for endometriosis (oral contraceptive use) increases the risk for IBD.
Strengths of the study, the authors write, include that the population has free, universal health care and excellent diagnosis registries that collect data prospectively, minimizing recall bias. The study covered many years and adjusted for age and period-specific IBD incidence in the general population.
Limitations of the study include omission of mild endometriosis cases and risk of ascertainment bias, as both types of diagnoses came from the same register. Another confounding factor might arise from the fact that the mean age at endometriosis was elevated (38.6 years), suggesting that some women may have been diagnosed when seeking infertility treatment.
The researchers conclude, "there is still a need for large-scale unselected cohort studies to confirm the influence of oral contraceptive use on the short- and long-term risk of IBD, not least in the context of concurrent endometriosis."
The lead author was supported by a grant from the Danish Council of Independent Research. The researchers have disclosed no relevant financial relationships.