Thyroid function and internal carotid artery stenosis in ischemic stroke.

Thyroid dysfunction has been known to be closely associated with increased vascular events. The aims of the present study included determining the prevalence of subclinical thyroid disease and relationships between normal ranges of thyroid function and internal carotid artery steno-occlusion (ICS) in patients with ischemic stroke. From March 2007 to February 2008, 382 consecutive patients with ischemic stroke referred to the neurovascular ultrasound laboratory were analyzed. ICS was defined as greater than 50% luminal narrowing or complete obstruction in at least 1 internal carotid artery. Subclinical thyroid disease was determined by free thyroxine (fT4) and thyroid stimulating hormone (TSH) measurements. After the exclusion of patients with abnormal levels of thyroid hormones, normal ranges of fT4 were classified into 3 groups: low-normal (fT4, 11.0~12.3 pmol/L), mid-normal (12.4~15.4), and high-normal (15.5~24.0) thyroid groups. There were 17 patients (4.5%) with subclinical hypothyroidism and 6 (1.6%) with subclinical hyperthyroidism. There were 301 patients (78.8%) with normal fT4 and TSH levels, and among them, 67 patients (22.3%) had ICS. There was a significantly higher percentage of ICS in the low-normal thyroid group than in the other groups. By multivariate regression analysis, the low-normal fT4 group had an OR of 2.80 (95% confidence interval, 1.39-5.66) for ICS compared to the mid-normal group. In patients with ischemic stroke, the prevalence of subclinical thyroid disease was similar to the general population, and in euthyroid patients, low-normal thyroid function was independently associated with a higher percentage of ICS.