Patients with subclinical thyroid disease have few abnormalities
and treatment has no proven benefit
(March 2004)
The background of the study. Subclinical hypothyroidism
and subclinical hyperthyroidism are defined, respectively, as high
or low serum thyrotropin (TSH) concentrations and normal serum free
thyroxine (T4) concentrations, independent of symptoms of thyroid
dysfunction. Whether patients with these disorders have problems
and benefit from therapy is debated.
How the study was done. The literature on subclinical
hypothyroidism and subclinical hyperthyroidism was reviewed by a
panel of experts in endocrinology, epidemiology, and preventive
health services. The panel rated the strength of the information
about the health effects and benefits of therapy of the two disorders
as good, fair, or insufficient.
The results of the study. The prevalence of subclinical
hypothyroidism was estimated to range from 4 to 8.5 percent among
adults in the United States. The panel found reasonable evidence
that subclinical hypothyroidism can progress to overt hypothyroidism
(high serum TSH and low free T4 concentrations) and that this progression
can be prevented by T4 therapy. The panel concluded that there is
little evidence that subclinical hypothyroidism is associated with
symptoms of hypothyroidism, cardiac dysfunction, or hypercholesterolemia,
or that T4 therapy is beneficial.
The prevalence of subclinical hyperthyroidism was estimated to
be 3.2 percent. The panel found reasonable evidence that subclinical
hyperthyroidism can progress to overt hyperthyroidism (low serum
TSH and high free T4 concentrations). The panel concluded that marked
(but not mild) subclinical hyperthyroidism is a risk factor for
atrial fibrillation (a cardiac rhythm disorder) and low bone density,
but that there is insufficient or no evidence to conclude that it
is associated with symptoms of hyperthyroidism or cardiac dysfunction,
or that these problems can be reversed or prevented by antithyroid
therapy.
The conclusions of the study. There is little
evidence that patients with subclinical hypothyroidism or subclinical
hyperthyroidism have any manifestations of thyroid dysfunction or
benefit from therapy. Population-based screening for these disorders
is not indicated.
The original article. Surks MI, Ortiz E, Daniels
GH, Sawin CT, Col NF, Cobin RH, Franklyn JA, Hershman JM, Burman
KD, Denke MA, Gorman C, Cooper RS, Weissman NJ. Subclinical thyroid
disease: scientific review and guidelines for diagnosis and management.
JAMA 2004;291:228-38.
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