Humoral autoimmune manifestation in subacute thyroiditis

To study the autoimmune manifestations in subacute thyroiditis (SAT), the patterns of thyroid antibodies, thyroglobulin and circulating immune complexes were investigated in 10 patients during the course of the disease. Eight patients were thyrotoxic at diagnosis, and became euthyroid during recovery with a median observation of 8 months (4-30 months). Thyroid stimulating immunoglobulins were measured as TSH binding inhibiting immunoglobulins (TBII) and as thyroid stimulating antibodies (TSAb). TBII were present in all patients at least once during the observation period and remained detectable in six patients after recovery. TSAb were detected in three patients without relation to the hyperthyroid state. Thyroglobulin antibodies (TgAb) were present in four patients and persisted in three, while microsomal antibodies (MAb) were negative. Thyroglobulin (Tg) in the TgAb negative patients (n = 6) was high at diagnosis (median 229 micrograms/l, range 55-375) and fell rapidly during the course of SAT. Circulating immune complexes (CIC), which were found in all patients, reached maximal levels shortly after the onset of the disease and persisted after recovery. No correlation could be demonstrated between the different thyroid antibodies, and there was no clear relation between the levels of CIC and presence of the autoantibodies. However, the changes in CIC paralleled the changes in TBII, and it is suggested that immune complex formation is a major feature of the regulatory mechanisms controlling the immune responses in SAT.