Subacute Thyroiditis with Highly Positive Thyrotropin Receptor Antibodies and High Thyroidal Radioactive Iodine Uptake

A 48-year-old woman with transient thyrotoxicosis, having a slightly high thyroidal 99mTc uptake (3.9% at 20 m) or radioactive iodine uptake (RAIU) (17.3% at 4 hour) and subacute thyroiditis (SAT)-like symptoms, signs and histological diagnosis (extensive cellular destruction and granulomatous inflammatory change), showed positive TRAb (59.9%) and TSAb (194%) activity. The high levels of TRAb and slightly high RAIU were still observed after one month of prednisolone treatment. Nine months later, the TRAb and TSAb levels finally normalized and her thyroid function has remained normal since then. We suspect that the slightly high RAIU were due to the presence of both the TRAb and the TSAb and the course of this case might mimic neonatal Graves' disease. (Internal Medicine 42: 704-709, 2003)