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