[Is there a need for treatment in subclinical hypo- and hyperthyroidism?].

Subclinical thyroid dysfunction is characterized by normal levels of thyroid hormones but abnormal values of thyrotropin (TSH) in an asymptomatic individual. Subclinical hypothyroidism is a common disorder with a prevalence of about 7 to 8% in women (most frequently in females over 50 years), and about 3% in men. It is characterized by elevated serum TSH in the presence of normal concentrations of serum thyroxine. Patients with TSH levels about 12 mU/L (and with positive antithyroidal antibodies) have the highest risk for developing overt hypothyroidism. Therefore, these patients will require L-thyroxine treatment. In patients with TSH < 12 mU/L, the indication for therapy depends on the etiology, on risk factors and concomitant diseases (e.g. strumectomy, coronary heart disease, depression, infertility). Subclinical hyperthyroidism (TSH suppression syndrome) is characterized by normal thyroid hormone concentrations but diminished serum TSH. Most frequently, this disorder is caused by exogenous L-thyroxine treatment. The endogenous form of subclinical hyperthyroidism mainly caused by nodular goiter has a prevalence of up to 20% in patients with large goiters. In patients with subclinical hyperthyroidism, there is an increased risk for development of atrial fibrillation and for a decrease in bone mass in postmenopausal women. In the majority of patients measurable TSH levels can be detected before or after stimulation with TRH. This formally excludes overt hyperthyroidism in such patients. Frequently, there is no need for treatment but follow-up is important. However, in patients with subclinical hyperthyroidism associated with atrial fibrillation a therapy with antithyroid drugs, beta-blockers or radioiodine must be considered.