Carcinomatous involvement of the thyroid presenting as subacute thyroiditis

Carcinomatous involvement of the thyroid is a most unusual cause of hyperthyroidism and thyroiditis, with only a few cases reported in the literature. The authors present a 35-year-old woman with signs, symptoms, and laboratory findings of hyperthyroidism, and subacute thyroiditis that was due to extensive replacement of the thyroid gland by adenocarcinoma (shown by fine needle aspiration). After chemotherapy with vincristine and cisplatin, the swelling of the thyroid resolved, thyroidal uptake of radioactive iodine increased, and mild hypothyroidism developed. Despite the improvement in her thyroid status, she died from progressive malignancy. This case illustrates the value of fine needle aspiration cytology where doubt exists in the diagnosis of thyroid disorders.