Subclinical Hyperthyroidism: A Review of the Clinical Literature

Subclinical hyperthyroidism (SCHyper) is a biochemical diagnosis characterized by a decreased serum thyroid-stimulating hormone (TSH) and normal serum thyroxine (T4) and triiodothyronine (T3) concentrations. Because SCHyper can be resolved, it is recommended to repeat serum TSH, T3, and T4 concentrations in 3 to 6 months before confirming a diagnosis of SCHyper to consider treatment. Proposed grading systems distinguish between mild (TSH, 0.1-0.4 mIU/L) and severe SCHyper (TSH, <0.1 mIU/L) and are used alongside patients' age and the presence of risk factors and symptoms to guide treatment. Appropriate evaluation includes an investigation of the underlying cause and assessment of an individual's risk factors to determine the necessity and type of treatment that may be recommended. SCHyper may be associated with increased risks of cardiovascular-related adverse outcomes, bone loss, and in some studies, cognitive decline. Treatment may include observation without therapy, initiation of antithyroid medications, or pursuit of radioiodine therapy or thyroid surgery. Considerations for treatment include the SCHyper etiology, anticipated long-term natural history of the condition, potential benefits of correcting the thyroid dysfunction, and risks and benefits of each treatment option. The purpose of this overview is to provide a guide for clinicians in evaluating and managing SCHyper in the routine clinical practice.