Endocrine Abstracts

Background: Subclinical hyperthyroidism is characterized by low or suppressed thyroid stimulating hormone (TSH) with normal thyroxine(T4) and normal Triiodothyronine (T3) on thyroid function test (TFT). It has various endogenous and exogenous causes. It may have subtle clinical signs and symptoms. Studies have shown that subclinical hyperthyroidism is associated with increased coronary heart disease mortality, atrial fibrillation, heart failure and fractures. Patients are offered treatment if over 65 years or in those under 65 years old who are symptomatic or with osteoporosis and heart disease.

Case: A 59-year-old female with background history of multinodular goitre and subclinical hyperthyroidism diagnosed in 2010 presented to GP new symptoms of fatigue. In 2010, she was diagnosed with 2 cm nodule in right upper lobe and had two negative fine needle aspiration cytology (FNAC). At that time, her TFTs showed subclinical hyperthyroidism with TSH <0.10 mU/l (0.35- 3.30 mU/l), FT3 of 5.3 pmol/l (3.0-7.0 pmol/l) and FT4 of12 pmol/l (10-25 pmol/l). She was discharged from clinic with plan of annual TFTs monitoring. On surveillance, she persistently remained subclinical hyperthyroid and asymptomatic. In 2025, she developed another nodule on same side of her neck which was referred to ear, nose and throat (ENT) for urgent review for suspected cancer. She was evaluated by ENT, and she was for conservative management given unchanged picture over last 15 years. At the same time, there was an incidental finding of atrial fibrillation on her smart watch. The assessment revealed she had persistent subclinical hyperthyroidism on biochemistry testing and ECG showed new atrial fibrillation. She was reviewed by cardiology team and had echocardiogram which showed dilated atria and reduced LVEF of 45%. She was treated with anticoagulation and bisoprolol. On endocrine review, she described that she is getting fatigue over last few months but denied any other specific symptoms of hyperthyroidism or palpitations. She was an ex-smoker, and her mother had thyroidectomy. Thyroid function test showed subclinical hyperthyroidism with suppressed TSH <0.01 mU/l (0.35-4.94 mU/l) and normal T3 of 5.5 pmol/l (2.4-6.0 pmol/l) and T4 of 14 pmol/l(8.0- 19.1 pmol/l). Both thyrotropin receptor and thyroid peroxidase antibodies were negative. In the context of long standing suppressed TSH and new atrial fibrillation, she was started on carbimazole.

Discussion points: When should treatment be considered in asymptomatic patients? Can we prevent all potential complications with early interventions? Treatment of choice medication versus low dose radioiodine? Does borderline thyroid function with positive antibodies need treatment?