Endocrine Abstracts

Background: Anaplastic thyroid carcinoma (ATC), which is one of the most aggressive endocrine tumors. Primary thyroid carcinoma typically does not interfere with thyroid function and presentation of ATC with thyrotoxic state is extremely rare. We present here an ATC patient who is complicated with thyrotoxicosis.

Case: A 69-year-old man presented with neck swelling and pointed out thyroid tumor with calcification two years ago. He appeared general fatigue, body weight loss and palpitation with elevated thyroid hormone, therefore he was transferred to our hospital for further examinations. Laboratory data showed thyrotoxicosis (TSH <0.05 μIU/ml, fT₃ 5.5 pg/ml, fT₄ 2.3 ng/dl) with negative TSH receptor antibody (TRAb <0.7 U/l), and a low grade uptake of ¹²³I scintigraphy in thyroid gland (0.2%). Ultrasonography showed diffuse goiter with low-echo levels and a 2.4 cm tumor with eggshell-like calcification at right lobe. Spontaneous remission was observed in thyrotoxicosis and it was consistent with destructive thyroiditis. One month later, he complained back pain and rib bone destruction was pointed out. Diffuse goiter was enlarged and diagnosed as ATC according to histological examination (TTF1 positive, p53 positive, MIB-1 index 30%). FDG-PET showed abnormal accumulation in thyroid, lung, bone and adrenals, which corresponded with multiple metastasis of ATC (Stage IVC). Multi-kinase inhibitor (Lenvatinib) was prescribed as treatment of ATC and RANKL inhibitor (Denosumab) was used against bone metastatic regions. However, these treatments were not effective and he moved to palliative care.

Conclusion: Thyrotoxicosis in ATC is very rare and only ten cases have been reported previously. Several explanations have been discussed in this phenomenon, and a representative theory is thyroid hormone leakage due to rapid tissue destruction, which is considered as same mechanisms in the present case.