RESUMEN
Subclinical hyperthyroidism is a state of increased thyroid function with few or no clinical definitive signs or symptoms of hyperthyroidism. It is characterised by a decrease of serum (TSH) concentration below 0.1 mU/L, when serum levels of total and free thyroxin and triiodothyronin concentration are within normal reference ranges. It is not a rare finding and rates between 0.02% and 11.3% have been reported in different groups. The clinical diagnosis of subclinical hyperthyroidism is very difficult in the absence of the typical symptoms of hyperthyroidism. Therefore the diagnostic evaluation is important, especially with the use of radioisotope scan. In nuclear medicine department we can confirm the provisional diagnosis by the use of thyroid scan. Recent studies reported the effects of subclinical hyperthyroidism on cardiovascular system, skeletal system, cognitive function, on quality of life and life expectancy especially in the elderly patient. Treatment is indicated in the presence of palpitation, or atrial fibrillation, in postmenopausal osteoporosis in women not on hormone replacement therapy, and in elderly patients in whom surgery is contraindicated. According to the opinions of European clinicians and clinician members of the American Thyroid Association, the majority recommend radical treatment for these patients. Radioiodine therapy is considered to be the treatment of choice in most of the patients with nodular goiter.