Hypothyroidism And Stroke: Is There A Link?

Hypothyroidism is a condition where the thyroid gland is underactive and doesn't produce enough thyroid hormone. Treatment requires taking thyroid hormone pills. Studies have shown that despite the widespread use of thyroid hormone treatment, overtreatment and undertreatment are common, but the long-term adverse effects of both are unclear. Some studies have shown that high thyroid hormone levels, as seen in hyperthyroidism, increase the risk of heart disease, specific atrial fibrillation, and stroke. However, it is not clear if high thyroid hormones produced by thyroid hormone medication for the treatment of hypothyroidism are associated with either atrial fibrillation or stroke.

A study by Karch and Thomas found a slight increase in the risk of stroke in patients with autoimmune thyroiditis compared to controls. Some of this increased risk of stroke was independent of cardiovascular risk factors. Another study found that subclinical hyperthyroidism and thyroid autoantibodies were associated with a poor outcome at 1 year in first-ever acute stroke patients, especially in those who presented with atrial fibrillation and a higher National Institutes of Health Stroke Scale (NIHSS) score at admission.

Hypothyroidism is linked to altered lipid metabolism and hyperhomocysteinemia

Hypothyroidism and Lipid Metabolism

Thyroid hormones regulate lipid metabolism by exhibiting specific effects on the liver and adipose tissue in a coordinated manner. Hypothyroidism is associated with an unfavourable effect on lipids. Substitution therapy is beneficial for patients with overt hypothyroidism, improving lipid profile. However, whether subclinical hypothyroidism should be treated or not is a matter of debate.

Hypothyroidism and Hyperhomocysteinemia

A study found that patients with acute ischemic stroke and hypothyroidism had a higher prevalence of hyperhomocysteinemia (45.4%) compared to euthyroid patients (27.8%).

Hypothyroidism may represent a modifiable stroke risk factor

Hypothyroidism is a common condition treated with thyroid hormone. However, the long-term adverse effects of both over- and under-treatment are unclear. Some studies have shown that high thyroid hormone levels, as seen in hyperthyroidism, increase the risk of heart disease, specific atrial fibrillation, and stroke. However, it is not clear if high thyroid hormones produced by thyroid hormone prescribed for treatment of hypothyroidism are associated with either atrial fibrillation or stroke.

Hypothyroidism and stroke risk factors

Hypothyroidism is linked to altered lipid metabolism and is associated with hyperhomocysteinemia. A study found that 12% of patients with acute ischemic stroke or transient ischemic attack had hypothyroidism. A significant difference was found between the prevalence of hyperhomocysteinemia in patients with hypothyroidism (45.4%) compared with euthyroid patients (27.8%). This suggests that hypothyroidism may represent a modifiable stroke risk factor.

Thyroid hormones and the brain

Thyroid hormones are of fundamental importance for brain development and are essential to warrant brain functions throughout life. Their actions are mediated by binding to specific intracellular and membranous receptors that regulate genomic and non-genomic mechanisms in neurons and glial cells, respectively. Mechanisms include the regulation of neuronal plasticity processes, stimulation of angiogenesis and neurogenesis, as well as modulating the dynamics of cytoskeletal elements and intracellular transport processes.

Thyroid dysfunction and stroke

Subclinical thyroid dysfunction could be found in stroke patients with positive thyroid autoantibodies. Subclinical hyperthyroidism and thyroid autoantibodies were associated with a poor outcome at 1 year in first-ever acute stroke patients, especially in those presented with atrial fibrillation and a higher National Institutes of Health Stroke Scale (NIHSS) score at admission.

Hypothyroidism is a common condition and is treated with thyroid hormone

Hypothyroidism is a common condition that can be treated with thyroid hormone therapy. However, the long-term adverse effects of this treatment are unclear. While studies have shown that high thyroid hormone levels can increase the risk of heart disease, specific atrial fibrillation, and stroke, it is uncertain whether high thyroid hormones produced by thyroid hormone medication for the treatment of hypothyroidism are associated with atrial fibrillation or stroke.

A 2014 study by Karch and Thomas found a slight increase in the risk of stroke in patients with autoimmune thyroiditis who were treated with thyroid hormone. However, other studies have found that subclinical hypothyroidism could be associated with a poor stroke outcome, especially in patients who presented with atrial fibrillation and a higher National Institutes of Health Stroke Scale (NIHSS) score at admission.

Some studies have also found that hypothyroidism before brain ischemia could have neuroprotective effects. However, there is no evidence from experimental studies that hypothyroidism after stroke has beneficial effects.

In conclusion, while hypothyroidism is a common condition that can be treated with thyroid hormone therapy, the effects of this treatment on stroke risk are still uncertain and require further investigation.

Subclinical hyperthyroidism and thyroid autoantibodies were associated with a poor outcome at 1 year in first-ever acute stroke patients

Subclinical hyperthyroidism and thyroid autoantibodies have been associated with a poor outcome at 1 year in first-ever acute stroke patients. In a study by Rania S. Nageeb et al., 34% of the 138 patients with acute stroke were found to have positive thyroid autoantibodies. Of these, 28% had subclinical hyperthyroidism, 21% had subclinical hypothyroidism, and 14% were euthyroid. The study found that 73% of stroke patients had poor outcomes at 3 months and 59% had poor outcomes after 1 year, with no significant difference between ischemic and hemorrhagic stroke patients. In the positive thyroid autoantibody group, the final TSH level, NIHSS score at admission, and disability at 1 year were significantly higher compared with the negative group. Poor outcome was significantly associated with higher NIHSS score at admission, positive thyroid autoantibodies, subclinical hyperthyroidism, and atrial fibrillation.

Another study by Sang-Hwa Lee et al. found that subclinical hyperthyroidism was associated with poor outcomes at 3 months and unsuccessful reperfusion in patients with acute ischemic stroke treated with reperfusion therapy. The study included 156 patients with acute ischemic stroke who received reperfusion therapy and found that 23.7% of patients had subclinical hyperthyroidism. The study found that the SCHyper group appeared to have poor functional outcomes, but the differences were not significant. However, compared with patients in the euthyroid state, patients with subclinical hyperthyroidism had an increased risk of poor functional outcomes at 3 months after a stroke (adjusted odds ratio [OR] 2.50, 95% confidence interval [CI] 1.01–6.14 for a mRS score of 3 to 6) and a decreased rate of successful reperfusion after reperfusion therapy (OR 0.13, 95% CI 0.04–0.43).

A third study by Xuting Zhang et al. found that 47% of 17 acute ischemic stroke patients with hyperthyroidism were found to have intracranial stenosis. The study found that the patients with intracranial stenosis had a higher prevalence of elevated antithyroperoxidase antibody (TPO-Ab), compared with those without intracranial stenosis (100% versus 33.3%, p=0.004), while thyroid function tests were not significantly different between the two groups.

Subclinical hyperthyroidism is a risk factor for poor functional outcome 3 months after ischemic stroke

A study by Frank Arne Wollenweber et al. found that patients with subclinical hyperthyroidism had a substantially increased risk of functional disability 3 months after stroke compared with subjects with euthyroid state. The study included 165 consecutively recruited patients admitted for ischemic stroke. The patients were divided into three groups: subclinical hyperthyroidism, subclinical hypothyroidism, and euthyroid state. The primary outcome was functional disability, and the secondary outcome was the level of dependency.

Another study by Sang-Hwa Lee et al. found that subclinical hyperthyroidism may be independently associated with a poor prognosis at 3 months and unsuccessful reperfusion in patients with acute ischemic stroke receiving reperfusion therapy. The study included 156 consecutively recruited patients with acute ischemic stroke receiving reperfusion therapy. The patients were divided into three groups: subclinical hyperthyroidism, subclinical hypothyroidism, and euthyroid state. The primary outcome was functional disability, and the secondary outcome was the successful reperfusion rate.

A third study by Louise D. McCullough et al. found that lower levels of free T3 were associated with poorer outcomes at hospital discharge, and at 3 and 12 months post-stroke. However, these associations diminished after correction for other known predictors of stroke outcome. The study included 129 patients with radiologically confirmed acute ischemic stroke. The patients were divided into three groups: euthyroid, hyperthyroid, and hypothyroid. The primary outcomes were in-hospital mortality and the National Institutes of Health Stroke Scale score on admission. The secondary outcomes included death or hospice after discharge, and the modified Rankin scale and modified Barthel Index at 3 and 12 months post-stroke.

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