Observations concerning the natural history of subclinical hyperthyroidism

Abstract

Objective: To examine the natural history of a subnormal serum thyroid-stimulating hormone (TSH) concentration with normal concentrations of both serum free thyroxine (FT4) and free triiodothyronine (FT3) (subclinical hyperthyroidism). PATIENTS, DESIGN, AND MEASUREMENTS: A retrospective analysis was undertaken and yielded 16 ambulatory patients who had presented with subclinical hyperthyroidism and were longitudinally followed with measurements of serum TSH and both FT4 and FT3 for a cumulative follow-up of 11 to 36 months. Seven of the patients had subclinical Graves' hyperthyroidism as judged from the presence of thyroid-stimulating immunoglobulins (TSI) in serum, and 9 had multinodular goiter confirmed with ultrasound and no TSI.

Results: In the 7 patients with TSI, serum TSH reverted to normal in 5 patients, with disappearance or decrease of TSI in 4, within 3 to 19 months. In 1 patient, subnormal serum TSH accompanied by both normal FT4 and FT3 has persisted for 15 months, and in a second patient serum TSH reverted to normal within 9 months, but at follow-up 27 months later overt hyperthyroidism had emerged. In the 9 patients with multinodular goiter, subnormal serum TSH accompanied by both normal FT4 and FT3 persisted during cumulative follow-up that ranged from 11 to 36 months.

Conclusions: This study suggests that the natural history of subclinical hyperthyroidism is variable, resolving or occasionally evolving in subclinical Graves' disease and persisting unchanged in multinodular goiter.