Subclinical hyperthyroidism: controversies in management

Subclinical hyperthyroidism is an increasingly recognized entity that is defined as a normal serum free thyroxine and free triiodothyronine levels with a thyroid-stimulating hormone level suppressed below the normal range and usually undetectable. The thyroid-stimulating hormone value is typically measured in a third-generation assay capable of detecting approximately 0.01 microU per mL (0.01 mU per L). Subclinical hyperthyroidism may be a distinct clinical entity, related only in part to Graves' disease or multinodular goiter. Persons with subclinical hyperthyroidism usually do not present with the specific signs or symptoms associated with overt hyperthyroidism. A detailed clinical history should be obtained, a physical examination performed and thyroid function tests conducted as part of an assessment of patients for subclinical hyperthyroidism and to evaluate the possible deleterious effects of excess thyroid hormone on end organs (e.g., heart, bone). A reasonable treatment option for many patients is a therapeutic trial of low-dose antithyroid agents for approximately six to 12 months in an effort to induce a remission. Further research regarding the etiology, natural history, pathophysiology, and treatment of subclinical hyperthyroidism is warranted.