Subclinical hypothyroidism may disappear
or progress to overt hypothyroidism
(November 2004)
The background of the study. Subclinical hypothyroidism,
defined as a high serum thyrotropin (TSH) and a normal free thyroxine
(T4) concentration, is common. It can disappear, but on the other
hand it can progress to overt hypothyroidism (high serum TSH and
low free T4 concentrations). In this study a group of patients with
subclinical hypothyroidism was followed to determine the frequency
of improvement or worsening.
How the study was done. The study subjects were
107 patients (93 women, 14 men; age range, 55 to 83 years) with
subclinical hypothyroidism detected initially as an incidental finding
and confirmed by repeat study 1 to 3 months later. Forty-four percent
had one or more symptoms and signs of hypothyroidism, and 76 percent
had a high serum antithyroid peroxidase (anti-TPO) antibody concentration.
Seventy-five patients (70 percent) had other medical problems, such
as diabetes mellitus or hypertension. The patients’ clinical
status was evaluated and serum TSH and free T4 were measured at
six-month intervals. Patients who had a serum TSH concentration
≥20 mU/L or a low serum free T4 concentration during follow-up
were considered to have overt hypothyroidism and were treated with
T4.
The results of the study. During a mean follow-up
period of 32 months, serum TSH concentrations became normal in 40
patients (37 percent), and 28 patients (26 percent) had progression
to overt hypothyroidism and were treated with T4 (Table). Normalization
of TSH secretion was more likely to occur in those with lower base-line
serum TSH values, and overt hypothyroidism was more likely to occur
in patients with higher base-line serum TSH values (Table).
The conclusions of the study. Among patients with
subclinical hypothyroidism, normalization of serum TSH values is
common in those with serum TSH values of 5.0 to 9.9 mU/L, and progression
to overt hypothyroidism is common in those with serum TSH values
of 15.0 to 19.9 mU/L.
The original article. Diez JJ, Iglesias P. Spontaneous
subclinical hypothyroidism in patients older than 55 years: an analysis
of natural course and risk factors for the development of overt
thyroid failure. J Clin Endocrinol Metab 2004;89:4890-7.
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