The Impact of Subclinical Thyroid Dysfunction on Cerebrovascular Pathology: A Focus on Carotid Atherosclerosis and Stroke Severity

Background: Thyroid dysfunction is a relatively common condition; however, the clinical relevance and long-term effects of subclinical thyroid dysfunction on cardiovascular and cerebrovascular morbidity remain uncertain. This study evaluated the association between subclinical thyroid dysfunction and cerebrovascular disease, focusing on lipid metabolism, carotid atherosclerosis, and stroke severity. Methods: This study included 80 adult patients consecutively admitted with acute ischemic stroke who were newly diagnosed with subclinical thyroid dysfunction. Patients were evaluated over a three-year period (2020–2022). Clinical data, extracranial carotid Doppler ultrasonography, and laboratory parameters (including TSH, FT4, and total cholesterol) were analyzed to establish correlations with stroke characteristics. Results: Subclinical hypothyroidism was identified in 83.75% of patients, while subclinical hyperthyroidism was present in 16.25%. A strong positive linear correlation was observed between serum TSH and total cholesterol levels (r = 0.794, p < 0.001). TSH levels significantly correlated with both the severity of carotid artery stenosis and the National Institutes of Health Stroke Scale (NIHSS) score in patients with anterior circulation stroke. Subclinical hyperthyroidism was identified as a protective factor against moderate or severe carotid atheromatosis (OR = 0.211, p = 0.038); however, 78% of these patients presented with newly diagnosed atrial fibrillation. Conclusions: Subclinical thyroid dysfunction is significantly associated with cerebrovascular pathology through distinct mechanisms. Subclinical hypothyroidism contributes to atherosclerotic vascular disease and greater stroke severity, whereas subclinical hyperthyroidism predisposes predominantly to arrhythmia-mediated embolic events.