Subclinical Hyperthyroidism: Case Report and Review of the Literature

Abstract

Subclinical hyperthyroidism is a biochemical diagnosis defined by a decreased serum thyroid-stimulating hormone (TSH) and normal serum thyroxine (T4) and tri-iodothyronine (T3) concentrations. The clinical presentation can vary widely, ranging from the lack of symptoms to overt symptoms of hyperthyroidism.

We present a case of a 66-year-old female with a history of hypertension, atrial fibrillation, systemic lupus erythematous, pre-diabetes, and osteoporosis who was found to have an incidental finding of subclinical hyperthyroidism. She also notes unintentional weight loss of 10 pounds over 2 months, anxiety, insomnia, heat intolerance, hand tremors, and palpitations which she initially attributed to aging. Her biochemical workup showed a serum TSH of 0.09 mIU/L (reference range, 0.3–4.7 mIU/L), free thyroxine (FT4) of 1.6 ng/dL (reference range, 0.8–1.7 ng/dL), and free tri-iodothyronine (FT3) of 400 (reference range, 222–383 pg/dL). Because of her age, underlying cardiovascular disease, osteoporosis, and TSH level being <0.1 mIU/L, the etiology of her subclinical hyperthyroidism was investigated for potential treatment. This patient was found to have a multinodular goiter, for which she received radioactive iodine therapy and thereafter converted to a euthyroid state. In this case report, we discuss the clinical presentation, workup, and treatment of subclinical hyperthyroidism.