Small cell lung cancer with metastasis to the thyroid in a patient with toxic multinodular goiter

Thyroid metastasis of lung cancer is rarely observed in clinical practice. The primary cancers which metastasize to the thyroid gland are mostly renal cell carcinoma, lung cancer, and breast cancer. Transient destructive thyrotoxicosis is caused by massive metastasis of extrathyroid tumors. We herein present a case report of a patient with small cell carcinoma of lung with metastasis to the thyroid and thyrotoxicosis due to toxic multinodular goiter. A 66-year-old man complained of swelling around the right side of the neck, dyspnea, progressive weight loss, and palpitation starting since 3 months before his admission. The patient was diagnosed with small cell carcinoma of lung with metastasis to the thyroid and thyrotoxicosis due to toxic multinodular goiter. The case report presented here illustrates the challenge of making a definitive and adequate diagnosis, particularly if the patient presents with 2 potential causes of thyrotoxicosis. Thyroid scintigraphy is an important tool for differential diagnosis of thyrotoxicosis.