[Lipid abnormalities in elderly patients with subclinical hyperthyroidism]

Sensitive thyroid-stimulating hormone (TSH) assays provide identification of many patients with subclinical hyperthyroidism resulting from excessive production or excessive replacement of thyroid hormone. Subclinical hyperthyroidism is defined by a TSH below normal (suppressed) with normal serum T3 and T4 levels. Subclinical hyperthyroidism is the goal of thyroid hormone therapy in patients with thyroid cancer, solitary thyroid nodules, multinodular or diffuse goiters, or a history of head and neck irradiation. Benefits of TSH suppression in these patients, were thought to exceed the risks of subclinical hyperthyroidism. Subclinical hyperthyroidism also occurs in patients with thyroiditis and those with autoimmune thyroid disease. Other causes of TSH suppression, such as use of glucocorticoids, severe illness and pituitary dysfunction should be excluded.

This investigation included 55 elderly patients with subclinical hyperthyroidism in order to establish the type and degree of lipid abnormalities and effects of therapy with antithyroid drugs (methimazole 10 mg/day) during three months. These patients presented with no or minimal symptoms of thyroid hormone excess, but 56% of patients experienced atrial fibrillation and cardiac hypertrophy.

Levels of serum cholesterol, LDL-cholesterol and HDL-cholesterol were decreased. We found a significant increase of serum cholesterol, LDL-cholesterol and HDL-cholesterol levels after treatment.

Subclinical hyperthyroidism in elderly individuals is difficult to diagnose because it may present only with cardiac manifestations including atrial fibrillation and cardiac hypertrophy. There is general agreement that measurement of serum TSH is the most sensitive indicator of thyroid hormone activity in its target tissues. Patients with subclinical hyperthyroidism tend to have low serum total cholesterol, LDL-cholesterol anf HDL-cholesterol levels. These values increase after treatment. Most patients with subclinical hyperthyroidism should be treated with antithyroid drugs to prevent cardiovascular complications and bone loss, particularly among postmenopausal women.