Historia natural del hipotiroidismo subclínico

Subclinical hypothyroidism is defined by elevated serum thyrotropin (TSH) levels in the presence of normal concentrations of circulating thyroid hormones. The prevalence of this hormonal alteration is high in the general population, especially in elderly women. The natural history of subclinical hypothyroidism has been assessed in several epidemiological surveys and, more recently, in systematic studies aimed at evaluating the incidence rate and risk factors for the development of definitive thyroid failure. In general, the mean annual rate of progression to overt hypothyroidism ranges from 3.3 to 11.4% per year. This incidence rate is higher in women, elderly patients, and those who have goiter, symptoms of hypothyroidism, or a positive thyroid autoantibody titer. However, the main factor in the evaluation of the risk of progression to overt thyroid failure is the initial TSH concentration. Treatment with levothyroxine in patients with subclinical hypothyroidism prevents the development of overt hypothyroidism and may improve symptoms and lipid profile, thus decreasing cardiovascular risk. Since this therapy is lifelong and is not problem free, careful and individualized evaluation of each patient should be performed before prescribing replacement therapy. Present recommendations include replacement therapy in patients with TSH levels greater than 10 mUI/L. In patients with serum TSH levels between 5 and 10 mUI/L periodic follow-up may be satisfactory to evaluate the tendency towards progression or stability of TSH levels.