A Case of Subacute Thyroiditis Accompanied by Thyroid Stimulating Antibodies and Thyroid Stimulation-Blocking Antibodies

After one month of suffering from cervical pain, subfever, palpitation and tachycardia, a 78-year-old woman came to our hospital. Tenderness was noted when we palpated her diffuse goiter. Thyroid stimulating hormone (TSH) level was less than 0.1μU/ml with high serum levels of free T3 (9.8pg/ml) and free T4 (4.4ng/dl), showing hyperthyroid state. Microsome test and thyroid test were both negative, with C-reactive protein (CRP) at 3.1mg/dl, erythrocyte sedimentation rate (ESR) at 139mm/hr and immunosuppressive acidic protein (IAP) at 881μg/ml. She was diagnosed as having subacute thyroiditis. However, thyroid scanning with 123I revealed normal uptake. TSH binding inhibitor Immunoglobulin (TBII) activity was 71.8%. Thyroid stimulating antibody (TSAb) was positive (869%). Thyroid stimulation-blocking antibody (TSBAb) was 22%. The histological examination by needle biopsy showed thyroid follicular cell destruction and appearance of giant cells, compatible with subacute thyroiditis. After administration of anti-inflam-matory drug alone, the cervical pain disappeared and CRP, ESR and IAP levels were normalized. Three months later, serum TSH level was 45.2μU/ml, free T3 was 2.4pg/ml and free T4 was 0.4ng/dl, showing hypothyroid state. TBII was 75.9%, TSAb was negative (122%) and TSBAb was positive (86%). Six months later, TBII, TSAb and TSBAb became negative and the thyroid function returned to normal. The occurrence of subacute thyroiditis may induce transitional multifunctional TSH-receptor antibody appearance.