Relapse of hyperthyroidism after hemithyroidectomy in concurrent medullary thyroid cancer and Graves' disease.

We present a rare case of concurrent medullary thyroid cancer (MTC) and relapse of Graves' disease (GD). A 26-year-old Chinese female suffered from GD for 1 year. Physical examination demonstrated mildly diffuse goiter with a palpable 1.0 cm nodule in the right thyroid lobe and exophthalmos. Before hemithyroidectomy, calcitonin was elevated and thyroglobulin was normal. After surgery, histopathological findings proved coexistence of MTC and GD. 16 months later, GD relapsed and radioactive iodine 131 therapy was given. Meanwhile, postoperative monitoring showed well controlled calcitonin and carcinoembryonic antigen. Our lesson demonstrates although concomitant of MTC and GD is very rare, yet after hemithyroidectomy for the single nodular MTC lesion, remnant thyroid lobe could be the source of GD relapse very soon. More importantly, the relapse of GD and the following radioiodine therapy and radiation exposure could have been prevented if a better therapy plan of total thyroidectomy was adopted in the first place, instead of hemithyroidectomy (Tab. 1, Fig. 2, Ref. 11).