Prevalence and Correction of Hypothyroidism in a Large Cohort of Patients Referred for Dyslipidemia

Abstract

Treatment of hypercholesterolemia can reduce the risk of developing premature atherosclerosis. The hypercholesterolemia caused by hypothyroidism is potentially reversible by thyroid hormone replacement therapy. We determined the prevalence of hypothyroidism in patients referred to a university lipid research clinic and studied the changes in lipid and lipoprotein levels on restoration of the euthyroid state. A retrospective follow-up study was performed. In all 1509 consecutive referrals for severe dyslipidemia, thyrotropin levels were measured. Patients with hypothyroidism were identified by means of a computed database, from January 1, 1989, to July 1, 1993, first by levothyroxine sodium medication and second by serum thyrotropin values greater than 5 mU/L. Twenty-one patients were available to evaluate the effect of restoration of the euthyroid state on plasma lipid and lipoprotein levels. The observed prevalence of hypothyroidism proved to be 4.2% (64/1509). The disorder was previously known in 25 patients and newly diagnosed in 39 patients (11 with overt hypothyroidism and 28 with subclinical hypothyroidism). Significant reductions in total cholesterol and low-density lipoprotein cholesterol levels occurred only in patients with pretreatment thyrotropin values of 10 mU/L or more. The prevalence of newly diagnosed cases of overt hypothyroidism in patients referred to a lipid clinic is approximately two times that in the general population. The absence of significant reductions in total cholesterol and low-density lipoprotein cholesterol levels on levothyroxine treatment in patients with minor subclinical hypothyroidism (thyrotropin level, < 10 mU/L) does not support the view that this condition is a risk factor for atherosclerosis mediated by an elevated low-density lipoprotein cholesterol level. All patients referred for diagnosis and treatment of dyslipidemia should be screened for hypothyroidism by measurement of thyrotropin values.