Context: One important aspect in the decision to treat or not elderly patients with subclinical hyperthyroidism (SCH) is the risk of progression to overt hyperthyroidism (OH).
Objective: To define the natural history of endogenous SCH in elderly patients with TSH between 0.1 and 0.4 mIU/l.
Design: Prospective study. One hundred and two women aged >or=60 years with persistently low TSH ranging from 0.1 to 0.4 mIU/l and normal free T4 and T3 were studied. Patients using L-T4 or antithyroid drugs, previously treated for hyperthyroidism, with pituitary disease, using corticosteroids, amiodarone, dopaminergic agonists, with atrial fibrillation or heart disease were excluded. Seven patients had Graves' disease, 91 had nodular disease and 4 presented no defined cause. The time of follow-up ranged from 12 to 70 months (median 41 months).
Results: Three patients progressed to OH (elevated T4 and/or T3) and four other patients to persistently low TSH (<0.1 mIU/l) in the presence of increase in serum T3 when compared with baseline. These patients were treated. Twenty-four women presented sustained normalization of TSH and none progressed to hypothyroidism. SCH with TSH in the 0.1-0.4 mIU/l range persisted in 71 patients, 4 of them (5.6%) being treated because of the development of atrial fibrillation or heart disease during follow-up. The only independent predictor of progression of SCH was an initial TSH value <0.2 mIU/l.
Conclusions: In elderly patients with endogenous SCH and TSH between 0.1 and 0.4 mIU/l progression to clinical hyperthyroidism is uncommon (approximately 1% per year), spontaneous TSH normalization may occur, and persistence of SCH for many years is the most likely.