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.
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