BERLIN – Women with endometriosis have nearly twice the odds of experiencing migraine headaches within a year of diagnosis than do those without the condition, according to a large, population-based, case-control study.
The findings of that study join conflicting data in the literature regarding comorbidity between migraines and endometriosis. For example, a genetic study of twins supports the relationship with an odds ratio of 1.57 (Genet. Epidemiol. 2009;33:105-13). Other researchers found a higher incidence of endometriosis among 22% of 171 women with migraine and 10% of 104 controls without migraine (Headache 2007;47:1069-78). In contrast, other investigators found that migraine was associated with chronic pelvic pain in a study of 108 women, but that endometriosis was not a significant factor (Fertil. Steril. 2011;95;895-9).
First author of the current study, Dr. Jong-Ling Fuh, a neurologist at the Neurological Institute of Taipei (Taiwan) Veterans General Hospital, said at the International Headache Congress that "there are many similarities between migraine and endometriosis."
For example, early menarche is a well-known risk factor for endometriosis, Dr. Fuh said. Menarche before age 12 years is also associated with increased prevalence of both migraine and nonmigraine headache (Eur. J. Neurol. 2011;18:321-8).
In addition, menorrhagia is a frequent complaint among women with endometriosis, Dr. Fuh said. In one study, for example, 63% of migraine patients reported recent history of menorrhagia, compared with 37% of controls (Headache 2006;46:422-8).
In the current study, migraines occurred in 1% of 20,220 women with endometriosis, which was significantly different from the rate of 0.5% seen in 101,100 women in a control group (odds ratio, 1.91).
Women with both conditions had similarly higher odds of first developing migraine (OR, 2.00) or endometriosis (OR, 1.85). However, after controlling for other clinical factors, researchers found that the association remained significant only when migraine preceded endometriosis (OR, 2.40), which suggests these headaches could predict endometriosis in some patients, Dr. Fuh said.
"Migraine was still an independent risk factor for endometriosis" after researchers controlled for patient age, medical history of infertility or pelvic pain, and previous laparoscopic surgery, Dr. Fuh added at the congress, which was sponsored by the International Headache Society and the American Headache Society. The data came from inpatient and outpatient ICD-9 codes in 2000-2007 in Taiwan’s National Health Insurance Research Database.
The study population included women aged 18-51 years (mean age, 38). Dr. Fuh reported that when the researchers examined only the 707 women who had migraine from either group, they found that endometriosis was more common among these migraineurs (28%) than in 19% of 120,613 of women without migraine.
A meeting attendee asked if the current endometriosis findings would remain statistically significant if pelvic pain was removed. "We did control for pelvic pain in our regression model, and pelvic pain and endometriosis were both independent risk factors [for migraine]," Dr. Fuh responded.
Although the physiological link between migraine and endometriosis remains unclear, Dr. Fuh proposed that the underlying mechanism for the comorbid association could be the "activation of sensory fibers within ectopic endometrial tissue, [leading] to hyperactivity of neurons throughout the central nervous system."
Use of a large database is a strength of the study, Dr. Fuh said. Potential limitations include a reliance on administrative coding and possible underdiagnosis of migraine. A meeting attendee commented that underdiagnosis of migraine could be a "big factor" with only 1% prevalence in the study. "I agree with you," Dr. Fuh said. "We need more education of primary care physicians about migraine ... to diagnose more."
Dr. Fuh had no relevant financial disclosures.