Endocrine Abstracts

Background: Functioning metastasis from a primary thyroid cancer are exceedingly rare. Failure to proceed to hypothyroidism after total thyroidectomy denotes remaining hormone production from functioning metastasis. Radioactive iodine ablation will ablate these remaining tissues. We present the case of a patient with follicular thyroid cancer, lung metastasis and detectable thyroid hormones after thyroidectomy.

Clinical presentation: The patient is a 71-year-old Filipina who had recurrent thyroid nodules for the past 22 years. She underwent four surgeries and the most recent was completion thyroidectomy for a 6.7×6.4×5 cm lobulated mass in the left thyroid bed. Preoperative TSH suppressed at 0.008 mIU/l (NV: 0.3–3.8) and free thyroxine was elevated at 36.2 pmol/l (NV: 11–24). Thyroid scintigraphy using 6 mCi of technetium 99m pertechnate showed functioning thyroid tissues with a conglomerate size of 8×5.6 cm. Chest CT scan revealed numerous small well-defined nodules scattered in both lungs. She was treated with Methimazole 20 mg daily for 4 weeks prior to surgery. Histopathology showed follicular carcinoma in the left thyroid lobe, the strap muscles and cervical lymph nodes. Three months after thyroidectomy, her TSH remained suppressed at 0.2 mIU/l and FT₄ detectable at 11.7 pmol/l. Diagnostic whole body scan using 3 mCi Iodine-131 showed two small foci of functioning thyroid remnant measuring 1.6×1.0 cm and 0.6×0.6 cm. Both lungs showed increased tracer uptake. A diagnosis of functioning lung metastasis was made. The patient underwent radioactive iodine ablation with 150 mCi of Iodine-131. Thyroid function tests done one month later revealed an elevated TSH 33.4 mIU/l and low FT₄ at 8.2 pmol/l indicative of successful ablation of functioning thyroid tissues.