Overt and 'subclinical' hypothyroidism in women.

UNLABELLED: Thyroid disease in general, and hypothyroidism in particular, are very common in women. In the USA, the most common cause of primary thyroid deficiency is on an autoimmune basis due to lymphocytic (Hashimoto) thyroiditis. Because there are thyroid hormone receptors in virtually every tissue of the body, the manifestations of hypothyroidism are varied, but problems with abnormal menses, conception, fertility, and pregnancy can be especially troubling in young women. The single most important diagnostic test is measurement of serum thyrotropin (TSH). The overwhelming majority of patients with hypothyroidism are treated with a single daily dose of synthetic levothyroxine with the goal of therapy being restoration of a normal metabolic state with return of the TSH level down to the range of 0.5 to 1.5 mlU/L. "Subclinical" hypothyroidism refers to those patients with early or mild thyroid hypofunction manifested as slight elevations of thyrotropin (approximately 4-10 mlU/L) although serum thyroxine (T4) and triiodothyronine (T3) levels are within their reference ranges. The entity is somewhat controversial in regard to its consequences if left untreated, and whether or not we should be screening patients, at least susceptible populations, for the condition. Reports indicate an association between subclinical hypothyroidism and poor outcomes of pregnancy, as well as dyslipidemias, atherogenesis, and increased mortality in the long term. We believe these consequences are sufficiently compelling to warrant screening and treatment with levothyroxine when found to halt progression to overt hypothyroidism, and improve symptoms, pregnancy outcomes, lipid abnormalities, and cardiovascular function.

TARGET AUDIENCE: Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES: After completion of this article, the reader should be able to recall that hypothyroidism is a common disease in women, has many protean manifestations, and can be successfully diagnosed and treated; explain that the condition of subclinical hypothyroidism can be diagnosed and if treated can prevent many untoward complications; and state that there should be heightened awareness of the disease so that proper screening tests can be performed.