ESPE Abstracts

Introduction: In rare cases, patients with thyroid hormone resistance syndrome may develop papillary thyroid cancer. There are only two reported cases of tumor development in children with this condition. Postoperative therapy is a difficult task, due to the persistent increase of thyrotropin (TSH) levels while receiving monotherapy with sodium levothyroxine, and the use of the drug in high doses leads to the development of thyrotoxicosis symptoms. Despite the fact that there have been no reported cases of cancer recurrence among this group of patients, the lack of achieving target TSH levels in children may increase the risk of papillary thyroid cancer recurrence.

Description: An 8.5-year-old patient presented with complaints of tachycardia. Examination revealed a normal TSH level of 4.35 mMU/l (0.51-4.82) with a high level of FT4 32.71 pmol/l (11.2-18.6) and FT3 15.93 pmol/L (4.1-7.1) accompanied by a diffuse thyroid enlargment. Based on the results of the hormonal profile and the absence of a typical presentationof thyrotoxicosis, it was suspected that the patient had a thyroid hormone resistance syndrome. A genetic test revealed a heterozygous variant of C.949G>A, A 317T in the THRB gene. At the age of 12.5 y. o., a nodule in the left lobe of the thyroid was detected (TIRADS 5, Bethesda V) and the patient underwent a thyroidectomy with central lymphadenectomy. Based on the results of the pathomorphological examination, the diagnosis stated "Papillary adenocarcinoma of the left lobe of the thyroid gland, stage T1bN0M0". After surgical treatment, the patient was prescribed levothyroxine sodium at an initial dose of 1.8 mg/kg/day. However, the patient's TSH level rose to 100 mIU/L while their FT4 and FT3 levels remained normal. Despite increasing the dose of levothyroxine sodium to 3.6 mcg/ kg / day, the TSH levels (74 mMU/l) were still increased and the patient complained of tachycardia and emotional instability. Therefore triiodothyroacetic acid was added to the treatment regimen at an initial dose of 0.35 milligrams per day. In the course of treatment with triiodothyroacetic acid at a dose of 1.05 mg/day and levothyroxine at 225 mcg/day, there have been positive changes in the form of a TSH decrease to 4.67 mMu/l. Given the low risk of thyroid cancer recurrence, the lack of an increase in TgAb and Tg, and the absence of cancer recurrence evidence, we have decided to forgo radiotherapy and continue with active follow-up monitoring.