Incidental medullary thyroid carcinoma in a case of Graves' disease.

In 1999, Brandle et al reported two patients with Graves' disease who had concomitant medullary thyroid carcinoma ( 1 ). The presence of medullary thyroid carcinoma was suspected in one patient who exhibited diarrhea three months after treatment with carbimazole and was detected by ultrasonography (2 cm in diameter). In the other patient, it was by Tc-99m pertechnetate scintigraphy (a 2-cm cold nodule). Here, we report a patient with Graves' disease who had incidental medullary thyroid carcinoma. A 32-year-old woman with Graves' disease was referred to our hospital for further treatment in May 1996. She was diagnosed as having Graves' hyperthyroidism in October 1994 and treatment with methimazole (MMI) was started. On physical examination, her thyroid gland was greatly enlarged and soft. Her blood pressure was 124/64 mmHg. Serum levels of free T3, free T4, and TSH were 2.4 pmol// (normal 3.4-5.7), less than 1.3 pmol// (normal 10.8-23.3), and 99.7 mU// (normal 0.43^.09), respectively, when she was on 20 mg/day of MMI. Her serum was positive for anti-TPO antibodies (37 U/ml, normal <0.3) and TSH-binding inhibitor immunoglobulins (54%, normal <15%), but negative for thyroid-stimulating antibodies (TSAb) (170%, normal <1 80) and anti-thyroglobulin antibodies (<0.3 U/ml, normal <0.3). Ultrasonic examination results using Aloka SSD-630 scanner with a 7.5-MHz ASU-32WL7.5 mechanical sector probe (Aloka Co., Tokyo) showed that