LOW TITER, COMPETITIVE INSULIN AUTOANTIBODIES ARE SPONTANEOUSLY PRODUCED IN AUTOIMMUNE-DISEASES OF THE THYROID

The occurrence of multiple endocrine autoimmunity with organ-specific autoantibodies is well known. In this study we evaluated the presence of competitive insulin autoantibodies (IAA) in immune and non-immune d iseases of the thyroid, utilizing a sensitive and specific radiobindin g assay. We studied 37 patients with Graves' disease, 44 patients with Hashimoto's thyroiditis, 11 patients with non-immune thyroid diseases and 30 normal controls. In 5/37 (13.5%), 7/44 (15.9%) patients with G raves' and Hashimoto's diseases, respectively, but in none of those wi th non-immune thyroid disease or of the controls, IAA levels exceeded our upper limit of normal range (50 nunits/ml) (P < 0.01). Positive IA A levels ranged between 50 and 123 nunits/ml with fluctuation of these levels over time. Islet cell antibodies were not detected in any of t he patients and the controls in the study. No association was found be tween propylthiouracil treatment and level of IAA. In none of 10 IAA-p ositive patients was the early phase insulin secretion of the intraven ous glucose tolerance test below 46 mu units/ml, and in 2 subjects rep eated tests after 3 years showed conserved insulin secretion. In concl usion, our findings show that 15% of patients with autoimmune thyroid diseases, produce specific IAA which do not seem to reflect aggressive beta cell destruction.