[A case of primary lung cancer complicated with hypothyroidism by diffuse thyroid metastasis].

A 56-year-old woman with hypothyroidism was admitted to our hospital because of an abnormal chest X-ray film. The chest CT showed a 3-cm spiculated tumor in the left lingual branch, and multiple nodular shadows with random distribution. Cervical CT showed diffuse enlargement of the thyroid gland with low density. The cytology of the tumor in the left lingular branch revealed adenocarcinoma, and ultrasound-guided fine needle aspiration cytology of the thyroid gland revealed adenocarcinoma, cytologically identical to the cells from bronchoscopic examination. Immunochemically, specimens obtained from both bronchoscopy and the thyroid gland were negative for thyroglobulin. Therefore, we diagnosed this case as primary lung cancer complicated with hypothyroidism by diffuse metastasis of the thyroid gland. Metastatic thyroid tumor is rarely diagnosed clinically. Furthermore, metastatic thyroid tumor complicated with thyroid dysfunction is extremely rare. We conclude that in patients with both diffuse thyroid swelling and thyroid dysfunction, the possibility of metastatic thyroid tumor should be considered.