What does this article add?
There is a significant increase in the carotid intima-media thickness in patients with subclinical hypothyroidism when compared to healthy controls, even in mild subclinical hypothyroidism. In addition, carotid intima-media thickness showed a significant reduction following treatment with levothyroxine.
The current study suggests that there is an increase in cardiovascular risk in subclinical hypothyroidism with TSH less or greater than 10 µIU/ml, and its treatment could potentially reduce this risk.
Introduction
The worldwide prevalence of overt hypothyroidism (OH) and subclinical hypothyroidism (SCH) ranges from 0.2-5%1,2 and 4.9-101,3 respectively. OH and SCH have been associated with dyslipidemia4, fatty liver disease,5,6 and decreased adrenal reserve.7 OH has also been associated with increased fatal and nonfatal cardiovascular disease.8,9 However, studies of the association of SCH and cardiovascular risk have shown controversial results, particularly in mild SCH (thyrotropin [TSH] <10µIU/ml).10 Some population databases have found an increase in coronary artery disease,11,12while other studies have shown a decrease or the absence of a correlation.13,14 Some methodological difficulties, however, restrict the clinical value of these findings since most came from uncontrolled studies. These included populations with cardiovascular risk factors or atherosclerosis markers that were used without a high correlation with cardiovascular outcomes.
Cardiovascular risk assessment in SCH has been analyzed by indirect markers, such as pulse wave velocity15 and aortic distensibility.16 In terms of cardiovascular risk prediction in the general population, the most studied marker of atherosclerosis is carotid intima-media thickness.17-19 The estimated risk for every 0.1 mm increase in carotid intima-media thickness is a 10 to 15% increase of myocardial infarction, and a 13 to 18% increase for stroke.17,20,21
Therefore, we carried out a prospective and controlled study in participants with SCH, OH, and healthy controls (HC) to determine, as a primary endpoint, the association between SCH and cardiovascular risk by measuring carotid intima-media thickness.
Materials and methods