Endocrine Abstracts

Introduction: Autoimmune thyroid disease is associated with other autoimmune diseases. However, most studies are register-based cohort studies or investigate selected patient populations. In a large national cross-sectional population-based study, we investigated positivity of thyroid peroxidase- or thyroglobulin-antibodies (TPOAbs or TgAbs) in association with non-thyroidal autoimmune disease.

Methods: As part of The Danish Investigation of Iodine Intake and Thyroid Diseases (DanThyr), two cross-sectional population studies with identical protocol were performed (1997–1998, n=4649, and 2004–2005, n=3570). Participation involved blood tests and questioning by a medical doctor on history of various diseases. TPOAbs and TgAbs were analysed by radioimmunoassay (DYNOtest, BRAHMS, Germany, cut-off: 60 U/ml). Non-thyroidal autoimmune diseases included rheumatoid arthritis, pernicious anaemia, vitiligo, and diabetes. Logistic regression analyses were adjusted for age, smoking, sex, cohort origin, and familial disposition. Ethical approval and informed consent were obtained.

Results: Of 8105 included participants, 1304 (16.1%) were TPOAb- or TgAb-positive. Hypo- or hyperthyroidism was reported by 2.8 and 2.9%, respectively; 0.6% reported both. Of the 937 (11.6%) participants reporting non-thyroidal autoimmune disease, 20.3% were thyroid antibody-positive (P<0.001 compared to participants without non-thyroidal autoimmune disease), 6.7% reported hypothyroidism, and 4.5% reported hyperthyroidism. In adjusted logistic regression analysis, thyroid antibody-positivity was associated with a significantly higher odds ratio of non-thyroidal autoimmune disease (14.6% vs 11.0%, P<0.001, adjusted odds ratio (aOR) 1.3 95%CI:1.1–1.5, P=0.008). In participants reporting hypothyroidism, 27.6% reported non-thyroidal autoimmune disease (vs 11.0%, P<0.001, aOR 2.5 95%CI:1.8–3.4, P<0.001). Hyperthyroidism was associated with nonthyroidal autoimmune disease (17.6% vs 11.3%, P=0.005); however, not in adjusted analyses (aOR 1.4 95%CI:0.96–1.9). Excluding participants reporting hypo- or hyperthyroidism, non-thyroidal autoimmune disease was still more prevalent in thyroid autoantibody-positive than -negative participants (13.1% vs 10.6%, P=0.01). Among the 190 participants with non-thyroidal autoimmune disease and thyroid autoantibody-positivity, 158 (83.1%) were TPOAb-positive. Participants with TPOAb-positivity combined with TgAb-positivity had similar frequencies of non-thyroidal autoimmune disease as those with isolated TPOAb-positivity (15.3% vs 15.1%). The prevalence among 32 participants with isolated TgAb-positivity was similar to that of thyroid antibody-negative participants (11.9% vs 11.0%, P=0.62).

Conclusion: More than 16% of the general population were thyroid autoantibody-positive, which (also without history of thyroid dysfunction) was associated with non-thyroidal autoimmune disease. Especially participants with reported hypothyroidism or TPOAb-positivity, but not those with isolated TgAb-positivity, had increased prevalence of non-thyroidal autoimmune disease. Attention should be paid to polyautoimmunity in patients with hypothyroidism and TPOAbs.