Women who have endometriosis are more likely than other women to have disorders in which the immune system attacks the body's own tissues, according to researchers at the National Institute of Child Health and Human Development (NICHD), the George Washington University, and the Endometriosis Association.
The researchers also found that women with endometriosis are more likely to have chronic fatigue syndrome and to suffer from fibromyalgia syndrome-a disease involving pain in the muscles, tendons, and ligaments. Women with endometriosis are more likely to have asthma, allergies, and the skin condition eczema. The researchers surveyed 3,680 women who said they had been surgically diagnosed with endometriosis.
"This study indicates that women with endometriosis may be more likely to have a variety of diseases involving the immune system," said Duane Alexander, M.D., Director of the NICHD. "Further study of the immune system in endometriosis may yield important clues to identifying the causes and treatment of the disease."
In women who have endometriosis, tissue like the lining of the uterus-the endometrium-grows in other parts of the abdominal cavity. The endometrial tissue may attach itself to the ovaries, the outside of the uterus, the intestines, or other abdominal organs. Endometriosis affects an estimated eight to ten percent of reproductive age women. It may cause infertility or pelvic pain, although researchers believe that some women with the disease may not experience symptoms. In addition, the researchers found that family members of women with endometriosis more commonly had the disease, as reported by others.
The researchers published their findings in the October 2002 issue of Human Reproduction.
Roughly 99 percent of the women in the study said they had experienced pelvic pain for about 10 years before they were diagnosed with endometriosis. The women in the study reported that their pain began shortly after their first periods. The researchers do not know whether endometriosis actually occurs at the first period or if it develops over time. It is also unclear whether treating pain early could prevent chronic pelvic pain from developing in these women. For this reason, the study authors suggested that physicians treating patients with pelvic pain--particularly adolescents--consider whether endometriosis might be causing the problem.
Ninet Sinaii, MPH, of NICHD's Pediatric and Reproductive Endocrinology Branch, and her colleagues analyzed information from a 1998 survey of members of the Endometriosis Association. The researchers focused on the 3,680 women who said they had been surgically diagnosed with the disease. The study authors compared the likelihood of women with endometriosis having a variety of disorders to the likelihood of women in the general population having these same conditions. These included:
- Autoimmune diseases--disorders in which the immune system attacks the body's own tissues.
- Chronic fatigue syndrome--a strong feeling of fatigue that lasts for at least six months without letting up.
- Fibromyalgia--a recurrent pain in the muscles, tendons, and ligaments.
- Endocrine diseases--disorders of the glandular tissue
- Atopic diseases--such as allergies or asthma
The researchers found that women with endometriosis were at greater risk than were other women for such autoimmune diseases as systemic lupus erythematosus, Sjögren's Syndrome, rheumatoid arthritis, and multiple sclerosis.
The women in the study were over a hundred times more likely to experience chronic fatigue syndrome than the general population of U.S. women. The women with endometriosis were more than twice as likely as other women to experience fibromyalgia. In addition, 20 percent had more than one other disease, and up to 31 percent of those with more than one disease had also been diagnosed with either fibromyalgia or chronic fatigue syndrome.
Hypothyroidism--an underactive thyroid gland-- was seven times more common in the endometriosis patients. In many cases, hypothyroidism may also be an autoimmune disorder, resulting from an immune system attack on the thyroid gland.
The researchers also found that the rates of allergies and asthma were higher among women with endometriosis than among women in the U.S. population, and higher still if they had other diseases. The researchers found that 61 percent of the women with endometriosis reported allergies (as compared to 18 percent of the general female population) and 12 percent had asthma (as compared to 5 percent). If a woman had endometriosis and an endocrine disease, the percent with allergies rose to 72 percent, and if a woman had endometriosis plus fibromyalgia or chronic fatigue syndrome, the rate for allergies rose to 88 percent.
Two-thirds of the women reported that relatives also had diagnosed or suspected endometriosis, suggesting a familial basis for the condition
The study authors cautioned, however, that the study may not be representative of all patients with endometriosis. First, the women may have joined the Endometriosis Association because they were experiencing pain from their condition and so may not be typical of all patients with endometriosis. Also, such self-reported surveys may be more open to error than are surveys taken by a trained interviewer. For example, some of the women who answered the survey may have misinterpreted questions, may not have recognized the names of specific diseases, or may not have accurately reported conditions experienced by their family members.
The women who responded to the Endometriosis Association survey were predominantly white (nearly 95 percent) and educated (90 percent had at least some college education), and ninety-one percent were of reproductive age (15-45 years old). To compensate for such possible sources of bias, the researchers conducted a type of statistical test known as a sensitivity analysis. This analysis helps to confirm that even if a disease is underestimated in the general population and overestimated in the study sample, the rates of the various conditions reported in women with endometriosis are probably still significantly higher than in the general population.
"These findings suggest a strong association between endometriosis and autoimmune disorders, chronic fatigue syndrome and fibromyalgia" said Ms. Sinaii. "Health care professionals may need to consider endometriosis when evaluating their patients for these disorders."
More information about endometriosis is available from the NICHD publication, Endometriosis, at http://www.nichd.nih.gov/publications/pubs/Documents/endometriosis-2002.pdf (PDF - 446 KB). Information about endometriosis is also available from the Endometriosis Association, 8585 North 76th Place, Milwaukee, WI 53223; phone, 414-355-2200; https://endometriosisassn.org/ 
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The NICHD is part of the National Institutes of Health, the biomedical research arm of the federal government. The Institute sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD Web site, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943; e-mail NICHDInformationResourceCenter@mail.nih.gov.
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