Endocrine Abstracts

Resistance to thyroid hormone beta (RTH?) is a rare disorder which poses challenges in both diagnostics and management. The prevalence varies from 1/19,000 to 1/40,000. In 14% of individuals manifesting with RTH? phenotype no THRB mutations were identified. The management of these patients, especially after total thyroidectomy, in the absence of generalized consensus is complicated. 36-year-old woman was referred to endocrinologist with symptoms of thyrotoxicosis and dissonant thyroid hormone levels (TSH 1.3-2.5 mU/l n0.4-3.6, FT4 22-30 pmol/l n7.87-20.3; FT3 5.5-8 pmol/l n3.34-5.14). Medical history revealed the exclusion of thyrotropinoma, toxic adenoma, autoimmune thyroid diseases. In 2009, she underwent hemithyroidectomy for thyroid nodules, at that time she was experiencing milder thyrotoxicosis symptoms. Post-surgery, she felt well for several years. Center endocrinologists suspected resistance to thyroid hormone, particularly RTH?, beta-blockers were prescribed and patient was referred for genetic testing. Despite that she was doing relatively well on propranolol, genetic results were pending, she declined to wait and insisted on a thyroidectomy (based on her well condition after hemithyroidectomy in 2009 and the presence of several 1-1,5cm diameter nodules near the isthmus). Thyroidectomy took place on 13-04-2023. After surgery, she was prescribed 100 mg of Levothyroxine per day. Approximately 1.5 months post-surgery, hypothyroidism was observed (TSH19.4; FT4 11.34; FT3 3.06), leading to an adjustment in Levothyroxine dosage to 100/125mcg. Genetic testing, at least for now, exluded thyroid pathology. Following the dose increase, she experienced a burning sensation in the chest area, spreading to the shoulders, back, and abdomen. Additionally, there was an increase in resting pulse rate to 120 beats/minute, heart palpitations, and a slight tremor in the legs. Beta-blockers were prescribed for tachycardia. The symptoms resolved after several days of discontinuing thyroxine. Due to possible intolerance, Euthyrox was prescribed, the symptoms worsened (severe headache, dizziness), prompting the patient to revert to L-thyroxine with a lower dose. No adverse symptoms were reported on levothyroxine 50mcg, but laboratory tests indicated hypothyroidism (TSH23.8; FT4 9.24; FT3 2.35). Novothyral was added, resulting in a with tachycardia and profuse sweating (beta-blockers were ineffective), leading to the discontinuation of Novothyral. The levothyroxine dose is currently being increased slowly (25mcg over 1-2 months), now on 100mcg p/d. Hypothyroidism is regressing, albeit slowly. Optimal management of RTH? cases is still not known, it seems that thyroidectomy brings a new challenges in postoperative hypothyroidism treatment. Because this pathology is rare, the best solutions can only come from sharing experiences, creating hope for a consensus soon.