MINIMALLY SYMPTOMATIC (SUBCLINICAL) HYPOTHYROIDISM

Subclinical hypothyroidism is defined by the presence of mild thyrotro pin (TSH) elevation but normal blood free thyroxine and free triiodoth yronine levels. The adjective ''subclinical'' seems awkward, if not in accurate, given that it is arguable whether these patients are truly a symptomatic and in view of the support in the literature for a salutar y effect of thyroid hormone therapy. In view of this and the evidence that the majority of such patients eventually evolve into overt thyroi d failure, we propose that a more appropriate term is minimally sympto matic hypothyroidism (MSH). The most common causes of this syndrome ar e the same as those for overt hypothyroidism and include chronic autoi mmune (Hashimoto's) thyroiditis, thyroid ablation with radioactive iod ine, antithyroidal drugs, and thyroidectomy. Ideally, the diagnosis is best considered in an outpatient setting, because confounding factors in hospitalized patients, such as severe systemic illness and medicat ions, can cause misleadingly elevated TSH levels. Although target orga n dysfunction is not as evident as in overt hypothyroidism, well desig ned studies have reported subtle elevations in atherogenic lipoprotein fractions, suboptimal left ventricular function, and discrete neurops ychiatric abnormalities. In minimally symptomatic patients, it is impo rtant to reconcile optimal medical practice with the increasing demand s of the current health care system for a judicious and cost effective approach to diagnosis and management. An initial clinical assessment for MSH could focus on identifying individuals vulnerable to thyroid d isorders, such as patients with a family or past medical history of th yroid disease, patients with a goiter or history of recent pregnancy, patients taking medications that could interfere with thyroid function , or patients with hypercholesterolemia. TSH should be measured in all patients at risk, and measurement of thyroid antibody titers may be u seful insofar as they confirm autoimmune thyroid disease and predict p rogression to frank hypothyroidism, especially in the geriatric popula tion. We believe that there is reason to expect benefits from initiati on of replacement therapy with levothyroxine, including relief of symp toms, improvement in lipid profiles and cardiovascular risk, and preve ntion of progression to overt hypothyroidism. Levothyroxine is given i n the usual recommended doses, with an ultimate target dose of approxi mately 1.7 mu g/kg, titrated accordingly to maintain serum TSH within the normal (measurable) range. Although still controversial, one recen t article suggests that screening women older than age 35 every 5 year s for MSH may be as cost effective as screening for breast cancer or h ypertension.