Endocrine Abstracts

Introduction: Resistance to thyroid hormone (RTH) is an inherited syndrome characterized by reduced responsiveness of target tissues to thyroid hormone (TH). It is characterized by high serum concentrations of free T₄ (Ft₄) and usually free T₃ (Ft₃) accompanied by normal or slightly high serum TSH concentrations. When RTH is suspected, the diagnosis should be confirmed by direct sequencing of the TR-β gene to identify mutations. Hurthle cell neoplasm (HCN) accounts for only about 3–10% of all differentiated thyroid cancers. To our knowledge; there isn’t any case reporting coexistence of HCN and RTH; so whe want to present this case.

Case report: A 38-year-old man presented with palpable goiter, tachycardia, nervousness, dysphagia and dyspnea. Thyroid function tests demonstrated a normal serum TSH of 1.21 μIU/ml but elevated fT₃ of 6.00 pg\ml and fT₄ of 2.44 ng\dl. He had normal α-subunit and partially suppressed TSH level by administration of incremental doses of L-T₃, and positive TSH response to TRH stimulation. Genetical testing was ordered to confirm diagnosis. His thyroid ultrasound showed hypoechoic nodule measuring 24×18×34 mm. FNAB of the nodule was compatible with folliculer neoplasm. Histopathological examination after total thyroidectomy revealed HCN with a focus of 20 mm in the long diameter at the nodule location, showing capsular invasion. Radioiodine ablation (RA) was planned.Waiting for RA, he was treated with 300 mcq L-T₄ and his TSH did not suppress, which will be also an important problem during the treatment and follow-up of HCN. The suppression of TSH could be difficult when HCN coexists with RTH. Increasing the dose of L-T₄ can result in thyrotoxicosis without TSH suppression.

Conclusion: In conclusion, this is the first case of reporting coexistance of HCN and RTH; management is more challenging.