Euthyroid status after total thyroidectomy due to functioning lung metastases from a clear cell variant of papillary thyroid carcinoma.

Background: Although functioning thyroid cancer metastases have been reported, they have almost never been reported for the clear cell variant of papillary thyroid carcinoma (PTC). Here we describe a patient with disseminated lung metastases of the clear cell variant of PTC who presented in the euthyroid state despite discontinuance of levothyroxine after total thyroidectomy.

Patient Findings: A 49-year-old woman underwent total thyroidectomy for the clear cell variant of PTC in March 2002. Levothyroxine replacement was initiated after total thyroidectomy, but the patient was lost to follow-up 5 years after the operation. She did not take any levothyroxine for 4 years. Upon presentation to our institution, her initial thyroid function tests were a serum thyroid-stimulating hormone (TSH) of 4.51 mIU/L (0.30-5.00), total triiodothyronine of 82 ng/dL (60-181), and free thyroxine of 1.21 ng/dL (0.89-1.76). The results of workups, including thyroid ultrasonography, chest computed tomography (CT) scan, and fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET)/CT, revealed that she had multiple metastases in the cervical lymph nodes and both lungs. She received 0.9 mg of recombinant human TSH (rhTSH) for 2 consecutive days followed by administration of 200 mCi 131I. A therapeutic whole body scan after 131I administration demonstrated intense uptake in the whole lung fields, suggesting functioning lung metastases.

Summary: It is extremely rare for metastatic PTC, even though it is a well-differentiated thyroid carcinoma, to produce a sufficient amount of thyroid hormones to result in euthyroid state after total thyroidectomy. To our knowledge, this is the first report of functioning lung metastases of the clear cell variant of PTC after total thyroidectomy that produced enough thyroid hormone to restore a euthyroid state.

Conclusion: Functioning metastases from recurred PTC, particularly of the clear cell variant, are very rare. When they occur, rhTSH is required to prepare these patients for treatment with ablative doses of radioactive iodine (131I).