Endocrine Abstracts

Differentiated thyroid cancers function less well than normal thyroid tissue but continue to secrete thyroglobulin (Tg) which can be iodinated to form thyroxine (T₄) and triiodothyroxine (T₃). Functioning metastases causing thyrotoxicosis are rare. The majority of reported cases have large volume, metastatic follicular tumours. A significant proportion develop T₃ toxicosis with normal T₄ levels. T₃ toxicosis is often mild. Clinical presentation is similar to that in other patients with thyrotoxicosis but metastatic disease is present. We describe a case of metastatic follicular thyroid cancer causing severe thyrotoxicosis and the clinical course following treatment.

An 82-year-old man with a large thyroid nodule was treated for thyrotoxicosis with carbimazole for 12 years. He subsequently developed widespread bone metastases including disease of his cervical spine. Pelvic biopsy confirmed metastatic, well differentiated, follicular thyroid cancer. Following total thyroidectomy at which a 7 cm widely invasive follicular thyroid carcinoma was removed carbimazole was discontinued. Thyrotoxicosis failed to resolve following surgery. He received propranolol and dexamethasone therapy in preparation for radioactive iodine (150 mCi) 4 weeks later. Whole body scan following radioactive iodine showed intense iodine uptake into bone metastases and no neck uptake. He was overtly biochemically thyrotoxic immediately before receiving radioactive iodine, free T₄ 75.2 pmol/l (12–22), free T₃ 32.6 pmol/l (3.1–6.8), TSH <0.03 mU/l (0.27–4.2), TSH receptor antibody <1 U/l, Tg 8955 μg/l, with no significant interference from anti-Tg antibodies, but had significantly improved 6 weeks later, free T₄ 27.1 pmol/l, FT₃ 10.1 pmol/l, TSH <0.03 mU/l, Tg 3704 μg/l.

A patient with metastatic follicular thyroid cancer causing severe thyrotoxicosis is described who following total thyroidectomy improved after radioactive iodine therapy. Medical management immediately before radioactive iodine included dexamethasone and propranolol but carbimazole was withdrawn. Further radioactive iodine therapy will be administered and when euthyroid may follow recombinant human TSH administration.