Introduction: Subclinical hypothyroidism is defined as an increased serum TSH and normal serum FT4 concentration. In subclinical hypothyroidism, thyroid peroxidase and thyroglobulin antibodies are frequently present. Subclinical hypothyroidism may have endogenous or exogenous causes. The prevalence of subclinical hypothyroidism is rather high. The number of patients progressing to overt hypothyroidism may be higher. These patients may be asymptomatic, or have only mild symptoms or a single symptom.
Material and methods: We investigated 35 patients with subclinical hypothyroidism in order to establish the type and degree of dyslipidemia and effects of therapy with L-thyroxine (50 micrograms/d) during three months.
Results: Serum cholesterol, LDL-cholesterol and apo B were increased. A significant reduction of serum cholesterol, LDL-cholesterol and apo B concentrations was established during thyroid hormone replacement.
Discussion and conclusion: Only a few studies reported higher LDL and lower HDL-cholesterol values in subclinical hypothyroidism. Much interest was thus aroused to evaluate whether or not subclinical hypothyroidism is associated with hypercholesterolemia. Only patients with serum thyrotropin (TSH) concentration above 10 mU/L had a significant reduction of serum cholesterol concentration during thyroid hormone replacement. Most patients with subclinical hypothyroidism should be treated with thyroxine to prevent progression to overt hypothyroidism. Thyroid hormone replacement therapy may slow the progression of coronary heart disease, because of its beneficial effects on lipids. These findings and especially high rate of progression towards overt hypothyroidism suggest early thyroxine treatment.