Development of hypothyroidism with thyroid stimulation blocking antibody long after treatment with antithyroid drugs in a patient with hyperthyroid Graves' disease: a case report

We observed a patient manifesting spontaneous hypothyroidism with thyroid stimulation blocking antibody (TSBAb) long after treatment with antithyroid drugs (ATDs) for hyperthyroid Graves' disease. A 19-year-old female with Graves' disease was treated with ATDs for approximately 2 years; after cessation of ATDs, hyperthyroidism did not recur. Nine years later, she was again seen in our hospital because of symptoms indicative of hypothyroidism. Thyroid hormone replacement was commenced after laboratory confirmation of hypothyroidism. TSH-binding inhibitor immunoglobulin and TSBAb were both positive, while thyroid stimulating antibody (TSAb) was negative, at the time of diagnosis of hypothyroidism. These results indicated that the alterations in thyroid function in this patient appeared to relate to the presumed decline in the activity of TSAb and the appearance of TSBAb years after ATDs administration had been discontinued.