Severe thyrotoxicosis induced by thyroid metastasis of lung adenocarcinoma: A case report and review of the literature

A 50-year-old woman who had undergone lung lobectomy because of lung adenoc arcinoma presented with thyrotoxicosis, neck swelling, and cervical lymphad enopathy one month after the operation. The total serum triiodothyronine (T -3) and thyroxine (T-4) levels were markedly elevated to 514 ng/dL and 26.4 mug/dL, respectively, and serum thyrotropin (TSH) was suppressed to less t han 0.005 muU/mL. Although the thyroid gland had been normal before surgery , chest computed tomography (CT) scan revealed a markedly enlarged thyroid gland only I month after surgery. 1231 uptake for 24 hours was suppressed t o 4% in the thyroid gland with no uptake elsewhere including the lung. Fine -needle aspiration cytology (FNAC) of the thyroid showed invasion of poorly differentiated adenocarcinoma cells, cytologically identical to the cells obtained from sputum and those infiltrating the resected sections of the lu ng adenocarcinoma. Immunohistochemical studies of resected lung tissues did not show positive staining for thyroglobulin, carcinoembryonic antigen (CE A), or surfactant protein A. Clinically, the thyrotoxicosis had spontaneous ly improved, followed by a hypothyroid state with shrinkage of the thyroid gland after chemotherapy. Despite repeated chemotherapy and the administrat ion of thyroxine for hypothyroidism, the patient died of respiratory failur e 9 months after the onset of thyrotoxicosis. From these findings and the c linical course, thyroid metastasis, developing subacutely from lung adenoca rcinoma, was diagnosed. We speculate that aggressive invasion of tumor cell s into the thyroid gland resulted in highly destructive thyrotoxicosis.