Subclinical Hyperthyroidism

Abstract

Subclinical hyperthyroidism is defined as normal serum free thyroxine and a free triiodothyronine level, with a thyroid-stimulating hormone level suppressed below the normal range and is usually undetectable. Although patients with this diagnosis have no or few signs and symptoms of overt thyrotoxicosis, there is sufficient evidence that it is associated with a relatively higher risk of supraventricular arrhythmias as well as the acceleration or the development of osteoporosis. Consequently, the approach to the patient with subclinical hyperthyroidism is controversial, that is, therapeutic intervention versus watchful waiting. Regardless, it is imperative for the referring physician to identify the causative thyroid disorder. This is optimally accomplished by a functional study, namely scintigraphy. Recognition of the scan findings of the various causes of subclinical hyperthyroidism enables the imaging specialist to help in diagnosing the underlying condition causing thyroid-stimulating hormone suppression thereby facilitating the workup and management of this thyroid disorder.

Early detection of biochemically occult autonomous thyroid nodules

“…In addition, atrial arrhythmias (sinus tachycardia, atrial premature beats and atrial fibrillation) are frequent sequelae of overt hyperthyroidism (5). Similar effects on cardiac function have been described even in subclinical hyperthyroid patients (8,9,10), mostly in the elderly (11). Indeed, atrial fibrillation (12) is diagnosed in 2% of euthyroid people, 14% of overt hyperthyroid patients and 13% of patients with subclinical hyperthyroidism (5,13).…”