Subclinical Hyperthyroidism

Subclinical hyperthyroidism is suppressed TSH with normal free T4 and T3.

• Prevalence 1 to 2% (up to 15% in older iodine deficient populations).
• Causes: exogenous levothyroxine (commonest), multinodular goitre, early Graves, toxic adenoma, thyroiditis.
• Risks: atrial fibrillation (TSH below 0.1 raises risk 2 to 3 fold), osteoporosis, fractures, cardiovascular mortality, dementia.
• Grades: mild (TSH 0.1 to 0.4), severe (below 0.1).

• Usually asymptomatic; mild palpitations, tremor, anxiety.
• Goitre or nodule; tachycardia.

• Repeat TSH, free T4, T3 in 2 to 3 months; exclude non thyroidal illness, drugs (glucocorticoids, dopamine), pregnancy (hCG).
• Thyroid scan/uptake, ultrasound, TSH receptor antibodies.
• ECG for AF, DEXA in postmenopausal women.

• Treat if TSH persistently below 0.1 and age over 65, cardiac disease, osteoporosis, or symptoms; consider if TSH 0.1 to 0.4 in older high risk patients.
• Endogenous cause: radioiodine or low dose methimazole 5 to 10 mg daily; thyroidectomy for large goitre.
• Exogenous: reduce levothyroxine to target TSH (except in thyroid cancer needing suppression).
• Beta blocker for symptoms or AF; anticoagulation by CHA2DS2 VASc.
• Otherwise observe with TSH every 6 to 12 months.