Thyroid Research Thyroid Research Archive Hypothyroidism

The severity of hypothyroidism is most likely to increase in patients with high serum thyrotropin values

(November 2002)

The background of the study. Subclinical hypothyroidism (high serum thyrotropin [TSH] and normal serum thyroxine [T4] concentrations) is common, and some patients later have overt hypothyroidism (high serum TSH and low serum T4 concentrations). In this study, the rate of progression to overt hypothyroidism was determined.

How the study was done. The study subjects were 82 women with subclinical hypothyroidism. The women were evaluated by clinical examination and measurements of serum TSH, free T4, antithyroid microsomal (peroxidase) antibodies, and lipids at yearly intervals. The study end points were overt hypothyroidism or initiation of T4 therapy.

The results of the study. There were no changes in mean symptom scores, serum lipid values, or serum free T4 concentrations during a mean follow-up period of 9 years (range, 0.5 to 26), whereas the mean serum TSH concentration increased from 12.0 to 18.9 mU/L. At base line, 21 women (26 percent) had serum TSH concentrations >4.0 to 6.0 mU/L, 36 women (44 percent) had values of >6 to 12 mU/L, and 25 women (30 percent) had values of >12 mU/L.

During follow-up, overt hypothyroidism developed in 23 women (28 percent), 56 (68 percent) had persistent subclinical hypothyroidism, and 3 (4 percent) became euthyroid. The likelihood of overt hypothyroidism increased as a function of the base-line serum TSH concentration. The 10-year risk was 0 percent in the 21 women with base-line serum TSH concentrations >4 to 6 mU/L, 43 percent (3 percent per year) in the 36 women with base-line concentrations >6 to12 mU/L, and 77 percent (11 percent per year) in the 25 women with base-line concentrations >12 mU/L. A high serum antithyroid microsomal antibody titer at base line was an additional risk factor for overt hypothyroidism. The cumulative incidence of overt hypothyroidism was 23 percent among the 40 women with normal serum antibody values and 58 percent among the 42 women with high serum antibody values at that time.

The conclusions of the study. Among women with subclinical hypothyroidism, the risk of overt hypothyroidism is higher in those with high serum TSH concentrations and antithyroid microsomal concentrations.

The original article. Huber G, Staub JJ, Meier C, Mitrache C, Guglielmetti M, Huber P, Braverman LE. Prospective study of the spontaneous course of subclinical hypothyroidism: prognostic value of thyrotropin, thyroid reserve, and thyroid antibodies. J Clin Endocrinol Metab 2002;87:3221-6.