Accelerated thyrotoxicosis induced by iodinated contrast media in metastatic differentiated thyroid carcinoma

A 67-yr-old woman who underwent total thyroidectomy 32 yr ago developed accelerated hyperthyroidism after injection of iodinated contrast media to evaluate a left hemipelvis mass. The patient was managed with propylthiouracil, beta-blockers and digoxin. Whole body ²⁰¹Tl and ¹³¹I scans demonstrated a functioning metastasis in the left hemipelvis where biopsy revealed a well differentiated follicular thyroid carcinoma. Palliative external beam radiotherapy was administered. The patient then received radioiodine treatment with granulocyte colony-stimulating factor to minimize bone marrow toxicity. Clinically significant thyrotoxicosis occurring in metastatic thyroid carcinoma is rare and results from abnormal ectopic thyroidal tissue iodine metabolism. Iodide-containing medications and contrast media should be avoided in patients with functioning thyroid metastases to prevent abrupt increases in circulating thyroid hormone levels.