الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Aging is the progressive, universal decline first in functional reserve and then in function that occurs in individuals over time. Aging is not a disease; however, the risk of developing disease is increased, often dramatically with age. The biochemical composition of tissues changes with age; physiologic capacity decreases, the ability to maintain homeostasis in adapting to stressors declines, and vulnerability to disease processes increases with age.
The endocrine organs, including the thyroid, are among the organs that undergo important functional changes during aging. With increase in age, marked changes in thyroid hormone production, metabolism, and action occur. There has been a long-standing controversy about the thyroid function test results in the elderly between those suggesting that aging is associated – in the absence of any thyroid disease – with lower TSH levels and others suggesting that serum TSH increases with age. However most current data support the view that serum TSH rises slightly with aging. Other changes associated with aging include age-dependent decline in serum FT3, whereas serum FT4 and TRH levels remain unchanged. The inactive metabolite rT3 seems to increase with age. There is an age-dependent increase in the prevalence of positive anti-thyroperoxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies, especially in females resulting in an increased prevalence of subclinical hypothyroidism. Other than hyperthyroidism and hypothyroidism, the elderly also have increased prevalence of thyroid nodules and thyroid neoplasms.
Subclinical hypothyroidism, defined as elevated serum TSH levels with normal circulating free thyroxine (FT4) level free, is more prevalent than overt hypothyroidism both in the general population and the elderly. SHT has the same etiology as overt hypothyroidism- the most common being autoimmune thyroiditis (Hashimoto’s disease) and previous treatment for hyperthyroidism. Other causes include treatment with thyroxine for hypothyroidism, radiotherapy to the head and neck, and therapy with drugs such as lithium and amiodarone.
SHT is mostly asymptomatic but patients may present with symptoms of actual hypothyroidism such as dry, cold skin or feeling colder, constipation, slower thinking, and poor memory.
SHT may resolve or progress to overt hypothyroidism. Other possible negative clinical outcomes of SHT include increased risk of cardiovascular diseases, cognitive impairment, dyslipidemia, atherosclerosis, arterial hypertension, reduced glomerular filtration rate, and neuropsychiatric symptoms.
Studies on the association between SHT and CHD have shown controversial results. While some studies have shown patients with SHT have increased risk of developing CHD, others concluded no increased CHD risk except in patients with TSH exceeding 10 mIU/ml and yet others have shown SHT is not associated with increased risk for CHD. Contrary to results of all these studies, one study showed a decreased cardiovascular and all-cause mortality in elderly people with SHT.
The present study was conducted aiming to evaluate if SHT is associated with higher risk of coronary heart diseases in the elderly individuals and to figure out if dyslipidemia and endothelial dysfunction assessed by flow mediated dilatation (FMD) of the brachial artery induced by occlusion and carotid artery intimal medial thickness (CIMT) are associated with SHT.
Fifty elderly individuals aged sixty five years and older were enrolled in this study and were divided into two groups, group 1: Thirty patients with subclinical hypothyroidism and group II comprising twenty age and sex matched euthyroid elderly serving as a controlled group. Serum TSH, FT4 and anti-TPO-Ab were measured to all patients by immune chemiluminescence , Subclinical hypothyroidism was defined as a TSH level greater than 4.5 mU/L in the presence of a normal free thyroxine level (0.8 to 1.7 ng/dL). Euthyroidism was defined as a normal TSH level (0.4 to 4.5 mU/L). group I was further stratified based on TSH levels into (TSH: > 4.5- <10 &TSH: >10). Complete lipid profile, thyroid ultrasound, echocardiography to assess cardiac function and markers of endothelial dysfunction namely carotid intimal medial thickness and flow mediated dilation of the brachial artery after occlusion were done to all cases as well.
The results were as follow:
There was no significant difference regarding age, sex, smoking status, lipid profile and hypertensive status between the SHT and euthyroid groups. No significant difference was found for cIMT in the sHT (mean 0.71 ± 0.16) and euthyroid controls (mean 0.66 ± 0.18). The percentage flow mediated vasodilatation was also not significant in the two groups (mean 16.20 ± 5.68; and 17.93 ± 5.47; respectively for the SHT and the euthyroid groups). Cardiac evaluation by echocardiogram showed 53.3% of the SHT elderly had unremarkable study, 36.7% had mild diastolic dysfunction while 10% had ischemic changes. In the euthyroid controls 65% had unremarkable study, and 35% had mild diastolic dysfunction. None had ischemic changes. There was no significant difference in the cardiac parameters between the two groups.
In conclusion, based on the data from the present study, minimal thyroid dysfunction (SHT) had no adverse effects on endothelial function in patients with SHT in our cohort and is not associated with increased risk for coronary heart diseases.