A Case of Graves’ Disease Developing During Levothyroxine Replacement Therapy After Thyroid Lobectomy

Thyroid hormone replacement therapy may be required in patients developing postoperative hypothyroidism after thyroid lobectomy. In the present study, we report the unexpected development of Graves’ disease in a patient who was receiving long-term hormone replacement therapy for postoperative hypothyroidism after lobectomy for papillary thyroid cancer. The patient, a 52-year-old woman, was under observation and hormone replacement therapy for postoperative hypothyroidism that had developed after thyroid lobectomy for papillary thyroid cancer. Her thyroid function had stabilized with the treatment, but around 87 months post-operatively, the patient showed signs of hyperthyroidism, and at 91 months post-operatively, she was found to have excessive thyroid hormone levels and her medication was discontinued. A careful evaluation revealed Graves’ disease as the cause of the hyperthyroidism. The mechanism of development of Graves’ disease after thyroid surgery remains unknown, and it is difficult to predict the development of postoperative Graves’ disease from preoperative tests, as the preoperative thyroid function is normal in most cases. In patients receiving hormone replacement therapy after thyroid lobectomy, fluctuations in thyroid function should be monitored, and in the event of any evidence of hyperthyroidism being detected, a careful evaluation should be performed to determine the cause of hyperthyroidism, such as Graves’ disease.