Evaluation of Endothelial Function in Subclinical Hypothyroidism and Subclinical Hyperthyroidism

Ayse S. Cikim; Huseyin Oflaz; Nese Ozbey; Kerim Cikim; Sabahattin Umman; Mehmet Meric; Ergin Sencer; Senay Molvalilar


Thyroid. 2004;14(8) 

In This Article

Abstract and Introduction

Subclinical hypothyroidism and subclinical hyperthyroidism are two frequently occurring conditions for which exact therapeutic approaches have not yet been established. The aim of this study was to compare the endothelial function and carotid artery intimae-media thickness (IMT) of these two groups of patients to euthyroid subjects and to assess the effects of these conditions on endothelial function. Study groups comprised of 25 subclinical hypothyroid patients (mean age, 32.28 ± 9.67 years), 13 subclinical hyperthyroid patients (mean age, 35.69 ± 9.67 years), and 23 euthyroid subjects (mean age, 35.87 ± 7.93 years). They were evaluated for flow-mediated dilatation (FMD), and carotid artery IMT. The groups were matched strictly for atherosclerotic risk factors. The subclinical hypothyroid group was found to have significantly lower FMD values. No significant differences were observed between the groups with respect to other vascular parameters. The only discriminative factor between the groups was the state of their thyroid function. Therefore, subclinical hypothyroidism may have adverse effects on endothelial function independent from other well-known atherosclerotic risk factors.

Subclinical Hypothyroidism (SH) is the most common thyroid disorder with frequencies of 7.5% and 2.8% for women and men, respectively, and increases up to 17.4% with advanced age in the former.[1–5] Because of the silent/nonspecific nature of the symptoms, and the lack of extensive trials on the consequence, an exact treatment model has not yet been established.[6] In addition, there is still a debate about the relationship between SH and acceleration of atherosclerosis.[7,8]

Although usually reported as being asymptomatic subjects with SH usually have mild hyperthyroidism symptoms.[9] Treatment is frequently suggested not only for arrhythmias, congestive heart failure, decreased exercise tolerance, thromboembolism as regards hyperdynamic circulation, and osteoporosis, but also for the risk of overt hyperthyroidism.[10–14]

In the last decade it has become apparent that dynamic aspects of vascular physiology, mainly the role of the endothelium and nitric oxide (NO), play a major role in the pathogenesis and clinical manifestations of coronary artery disease.[15] A noninvasive technique using high-resolution external ultrasound allows the assessment of brachial artery endothelial-dependent response.[16] Many blood vessels respond to an increase in flow (shear stress) by dilatation. This phenomenon is called flow-mediated dilatation (FMD).[17] Measuring intimae-media thickness (IMT) of the carotid artery by ultrasound is another accepted method for detection of early atherosclerotic changes, which has been proven to be directly related to coronary artery disease.[18–20]


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