Effect of L-thyroxin therapy on thyroid volume and carotid artery lntima-media thickness in the patients with subclinical hypothyroidism

Background: Subclinical hypothyroidism (SCH) is mild-to-moderate thyroid insufficiency that is characterized by thyrotropin (TSH) level higher than the upper limit despite normal serum free thyroxin (fT4) level. Likewise, SCH as well might be a risk factor for cardiovascular diseases. Some placebocontrolled studies showed beneficial effect of L-thyroxin replacement on the risk for early atherosclerosis and CVD in the patients with SCH. Methods: Fifty-six patients presented to our clinic with subclinical hypothyroidism were included in the study. Forty-six healthy euthyroid subjects were included as the control group. Patients with fT4>0.61ng/ dl and TSH>4.2 uIU/ml were considered as SCH. Serum LDL and HDL cholesterols, triglyceride level, thyroid antibodies (anti-TPOAb and anti-TgAb), and fasting plasma glucose levels of the patients and the control group were measured. Carotid artery intima-media thickness (CIMT) was measured via B-mode ultrasonography and thyroid volume was calculated. L-thyroxin replacement was commenced at a dose of 25-50 mcg/day. CIMT and thyroid volumes of the patients were reevaluated six months after they became euthyroid. Results: A statistically significant difference (p<0.05) was found between the CIMT values before and after the L-thyroxin therapy in the SCH group. Pretreatment CIMT values were significantly higher than the post-treatment CIMT values (p=0.0001). There was significant difference also between the pre-treatment and post-treatment thyroid volumes in the SCH group (p<0.05). Conclusion: The present study showed the reduction in CIMT with L-thyroxin therapy in the patients with subclinical hypothyroidism. Therefore, thyroid hormone replacement might help to slow down or prevent atherosclerosis in the subclinical hyperthyroidism as well.