Objective: Autoimmunity plays an important role in the development of thyrotrophin (TSH) receptor antibodies and the pathogenesis of Graves' disease and Hashimoto's thyroiditis. On the other hand, subacute thyroiditis is a self-limited inflammatory disease of presumed viral aetiology. The aim of this study was to examine whether subacute thyroiditis triggers TSH receptor antibody-associated thyroid disorders.
Patients: We reviewed 1,697 patients with subacute thyroiditis seen between 1985 and 1995.
Design and measurements: We measured antibodies which inhibit the TSH binding to the TSH receptor (TBIAb), thyroid stimulating antibodies (TSAb) and antibodies that block TSH action (TBAb). Other thyroid autoantibodies were also determined.
Results: TBIAb became positive in 38 patients following subacute thyroiditis. Thyroid function after the development of TBIAb appeared to be influenced by the bioactivity of the antibody. Hyperthyroidism developed in the presence of TSAb, and so did hypothyroidism in the presence of TBAb, although 21 patients did not have thyroid dysfunction despite high titres of TBIAb. Fifteen out of 17 patients recovered from hyperthyroidism or hypothyroidism after the disappearance of TBIAb sometimes even without medication. TBIAb-positive patients had a high incidence of a family history of thyroid disease and positive anti-thyroid microsomal antibodies. An ophthalmopathy similar to Graves' disease was also observed in 3 patients.
Conclusions: Subacute thyroiditis may trigger autoreactive B cells to produce TSH receptor antibodies, resulting in TSH receptor antibody-associated thyroid dysfunction in some patients.