CHICAGO — Nearly 10% of patients with Graves' disease and more than 14% with Hashimoto's thyroiditis had a coexisting autoimmune disease, in an unusually large British study.
These prevalence rates are so high that it makes sense to screen for additional autoimmune diseases in all patients who have autoimmune thyroid disease and who present with new symptoms, Dr. Kristien Boelaert said at the annual meeting of the American Thyroid Association.
She reported on a prospective national U.K. study involving 3,286 white subjects with autoimmune thyroid disease–2,791 with Graves' disease and 495 with Hashimoto's thyroiditis–and their parents.
The parents, too, proved to have significantly elevated rates of having autoimmune diseases, compared with current prevalence figures for the general U.K. population, according to Dr. Boelaert of the University of Birmingham (England).
Rheumatoid arthritis was the most common comorbid autoimmune disease in individuals with autoimmune thyroid disease. Vitiligo was No. 2, followed by pernicious anemia, then type 1 diabetes (see box).
The parents also had increased relative risks of most autoimmune diseases included in the study. Parents of patients with Graves' disease had an increased prevalence of hyperthyroidism, while Hashimoto's thyroiditis clustered with parental hypothyroidism.
A history of thyroid dysfunction was given by the mothers of 17.5% of individuals with Graves' disease and by 23.6% of those whose child had Hashimoto's thyroiditis.
Likewise, the fathers of 3.1% of the patients with Graves' disease had a history of thyroid dysfunction, as did 5.7% of fathers of individuals with Hashimoto's thyroiditis.
The prevalence of many coexisting autoimmune diseases was similar in patients with Graves' disease and those with Hashimoto's thyroiditis. But there were a couple of differences: Addison's disease and pernicious anemia were far more common in the group with Hashimoto's thyroiditis.
Moreover, there were a few sex differences in rates of coexisting autoimmune diseases.
For example, rheumatoid arthritis was more than threefold more common among females than among males with Hashimoto's thyroiditis, whereas the prevalence didn't vary significantly by sex in patients with Graves' disease.
These observed differences in disease prevalence may reflect differences in the distribution of susceptibility genes and/or environmental triggers for the coexisting autoimmune diseases. Investigating this possibility will be a priority in the ongoing study, which includes DNA samples from all patients and parents.
The study, unprecedented in its size, provides the first definitive data on associations between autoimmune thyroid disease and coexisting autoimmune diseases, according to Dr. Boelaert.
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