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Fluctuating Thyroid Function in Graves' Disease - A Report of Two Cases
摘要
Background. Graves' disease is an autoimmune thyroid disease characterized by autoantibody production. The disease course varies from persistent hyperthyroidism to cyclic changes from hyperthyroidism to euthyroidism. Most patients gradually achieve remission; however, some eventually develop hypothyroidism because of destructive lymphocytic thyroiditis. Methods. We report two cases of Graves' disease with unusual thyroid function fluctuation: hyperthyroidism, followed by transient hypothyroidism and hyperthyroidism. These fluctuations were not attributable to the effects of antithyroid drugs. Results. Case 1-A 60-year-old woman presented with body weight loss, palpitation, hand tremors. Thyrotoxicosis (thyroid-stimulating hormone [TSH]: 0.0016 uIU/mL; free thyroxine [free T4]: 3.49 ng/dL) was diagnosed and started on methimazole treatment. After 2 months, she developed a hypothyroid status (TSH: 30.11 μU/mL; free T4: 0.41 ng/dL), which persisted after the 1-month discontinuation of methimazole. Therefore, she was started on levothyroxine treatment. After 8 months, low TSH levels (TSH: 0.066 μU/mL; free T4: 1.17 ng/dL) were observed, and methimazole treatment was repeated. She gradually became euthyroid, following which methimazole treatment was discontinued. Case 2-A 67-year-old man had thyroid function fluctuation similar to that in case 1. Conclusion. A possible explanation of the unusual thyroid function fluctuation in autoimmune thyroid disease is alternating thyrotropin receptor (TSHR) stimulating and blocking of antibody activity; however, TSHR-blocking antibodies could not be measured in this study. Furthermore, in some patients with Graves' disease, short-term follow-up of thyroid function is necessary to adjust treatment appropriately.