Hyperthyroidism And Stroke: Is There A Link?

Hyperthyroidism is a condition where the thyroid gland is overactive and produces excess thyroid hormones. It has been linked to an increased risk of heart disease and atrial fibrillation, which is a known cause of cardioembolic stroke. While the direct link between hyperthyroidism and stroke is not yet fully understood, some studies suggest that hyperthyroidism may be a contributing factor to stroke in certain cases. This is particularly true for young adults, where hyperthyroidism has been associated with a higher risk of ischemic stroke. The relationship between thyroid function and stroke recovery is complex and requires further investigation.

Hyperthyroidism and risk of ischemic stroke in young adults

Hyperthyroidism is a condition where the thyroid gland produces an excess of thyroid hormones. It has been linked to cerebrovascular disease, but its role as a potential risk factor for stroke in young adults has not been established. This study aims to investigate the association between hyperthyroidism and the risk of ischemic stroke in young adults aged 18 to 44 years old.

Methods

This was a 5-year follow-up study that included 3176 patients with hyperthyroidism as the study cohort and 25,408 patients without hyperthyroidism as the comparison cohort. Ischemic stroke development was tracked for each patient over 5 years, and Cox proportional hazard regressions were used to calculate the 5-year stroke-free survival rate between the two cohorts.

Results

During the 5-year follow-up period, 198 patients (0.7%) experienced ischemic strokes, with a higher proportion in the hyperthyroidism cohort (1.0%) than in the comparison cohort (0.6%). After adjusting for various factors, the hazard of having an ischemic stroke was 1.44 times greater for patients with hyperthyroidism compared to those without.

The study concludes that hyperthyroidism is associated with an increased risk of ischemic stroke among young adults. This finding highlights the importance of considering hyperthyroidism as a potential risk factor for stroke in this age group. Further research is needed to understand the underlying mechanisms and develop effective preventive measures.

Thyroid storm and ischemic stroke

Hyperthyroidism can cause a stroke, with one source stating that the risk of ischemic stroke is 1.44 times greater for patients with hyperthyroidism than for patients without. Thyroid storm coexisting with ischemic stroke is a rare but dangerous occurrence, with a mortality rate of up to 100% without appropriate treatment.

Ischemic stroke can be both the cause and the effect of thyroid storm. In the former case, the stroke can be caused by atrial fibrillation or a hypercoagulable state, both of which are associated with thyrotoxicosis. In the latter case, the thyroid storm can be precipitated by the acute illness caused by the stroke.

The treatment of coexisting thyroid storm and ischemic stroke requires adjustments to the management of both conditions. For example, aspirin should be avoided, and Clopidogrel may be considered as an alternative.

A case study of a 63-year-old male with bipolar disorder, alcohol abuse in remission, hypertension, and medical non-compliance presented for evaluation of left-sided weakness and slurred speech. The patient was found to be hypertensive and tachycardic, with mild exophthalmos and notable neurological findings of left-sided facial droop and left hemiparesis. The patient was diagnosed with hyperthyroidism with thyroid storm and was treated with propylthiouracil, potassium iodide, and glucocorticoids. The patient's symptoms improved significantly, and he was discharged to an inpatient rehabilitation center.

Hyperthyroidism and atrial fibrillation

Hyperthyroidism is a well-known cause of atrial fibrillation, with a prevalence of 16%–60% in patients with hyperthyroidism. Atrial fibrillation is the most common arrhythmia worldwide, and its frequency increases with age.

In a large population-based study, all patients with new-onset hyperthyroidism were followed for around 30 days from diagnosis to observe for new-onset atrial fibrillation or atrial flutter. It was found that 8.3% of such patients had a new-onset diagnosis of atrial fibrillation or atrial flutter. In patients with hyperthyroidism, it was found that those who were male, of advancing age, or had coronary artery disease, congestive heart failure, or valvular heart disease were more likely to have atrial fibrillation.

In a large nationwide cohort study, patients who were diagnosed with new-onset atrial fibrillation were followed for 13 years to identify if they would develop hyperthyroidism. In the 13-year follow-up, there was a significantly higher incidence of hyperthyroidism, particularly in the male population aged 51–60, when compared to the general population of that age without a diagnosis of atrial fibrillation.

Hyperthyroidism can occur due to an overactive thyroid gland or the passive release of stored thyroid hormone. It is generally considered overt or subclinical, depending on the biochemical severity of the hyperthyroidism. Overt hyperthyroidism is defined as suppressed (usually undetectable) thyrotropin (TSH) and elevated levels of triiodothyronine (T3) and/or estimated free thyroxine (free T4). Subclinical hyperthyroidism is defined as a low or undetectable serum TSH with values within the normal reference range for both T3 and free T4.

Atrial fibrillation has been known to significantly increase the risk of developing stroke and thrombotic episodes. The current guidelines use the CHA2DS2-VASC scoring system to predict who is at increased risk for a thrombotic episode and would benefit from anticoagulation. Atrial fibrillation with hyperthyroidism has been studied in various trials with varying results. Some studies have shown that hyperthyroidism and atrial fibrillation independently increase the risk of a thrombotic episode, particularly embolic events to the central nervous system early in the course of the disease. However, other studies have not found hyperthyroidism to be an independent risk factor for thrombosis in those with atrial fibrillation.

In patients with hyperthyroidism-related atrial fibrillation, there is no clear consensus on the efficacy of catheter ablation. Some studies have found circumferential pulmonary vein ablation to be a viable therapeutic option, while others have found that a single ablation has a lower efficacy when compared to patients with paroxysmal atrial fibrillation without a history of amiodarone-induced thyrotoxicosis (AIT).

Hypothyroidism and stroke risk

Hypothyroidism is a common condition treated with thyroid hormone therapy, typically involving lifelong thyroid hormone medication. However, despite its widespread use, overtreatment and undertreatment are common, and the long-term adverse effects of both are unclear. Studies have shown that high thyroid hormone levels, as seen in hyperthyroidism, increase the risk of heart disease, atrial fibrillation, and stroke. However, it is unclear if high thyroid hormones produced by thyroid hormone medication for treating hypothyroidism are associated with an increased risk of stroke.

Stroke is a leading cause of death and serious disability, and while there is extensive knowledge about risk factors, many of these factors are unchangeable, such as age and sex. Therefore, attention has shifted towards identifying modifiable risk factors to reduce stroke risk.

A study by Papaleontiou et al. (2021) investigated the association between abnormal thyroid hormone levels in patients taking thyroid hormone medication and the risk of stroke. The study included 733,208 adult patients receiving thyroid hormone therapy and followed them between 2004 and 2017. Patients with thyroid cancer or those on lithium or amiodarone were excluded, as these can alter thyroid function test results. The findings revealed that 11.08% of patients developed atrial fibrillation, and 6.32% experienced an acute stroke during the study period.

Importantly, patients taking thyroid hormone medication with very low TSH levels (<0.1) or high free T4 levels had a higher risk of stroke and atrial fibrillation compared to those with normal TSH and free T4 levels, even after controlling for other risk factors. Interestingly, patients with high TSH or low free T4 levels (undertreatment) also had a higher risk of atrial fibrillation than those with normal thyroid hormone levels. The study concluded that maintaining normal thyroid levels in patients treated with thyroid hormone medication is crucial to reducing the risk of stroke and atrial fibrillation.

Another study by Sheu et al. (2010) specifically examined the association between hyperthyroidism and the risk of ischemic stroke in young adults. The study included 3176 patients with hyperthyroidism and 25,408 patients without hyperthyroidism as a comparison cohort. The results showed that 1.0% of the hyperthyroidism patients and 0.6% of the comparison cohort experienced ischemic strokes during the 5-year follow-up period. After adjusting for various factors, the hazard of having an ischemic stroke was 1.44 times greater for patients with hyperthyroidism than for those without.

Additionally, hypothyroidism can cause hypertension, hypercholesterolemia, cardiac dysfunction, and both hypo- and hypercoagulability, all of which are risk factors for stroke. Therefore, it is essential to carefully manage thyroid hormone levels in patients with hypothyroidism to minimize the risk of stroke and other cardiovascular complications.

In conclusion, while hypothyroidism itself is not a direct cause of stroke, improper management of thyroid hormone levels in patients with hypothyroidism can increase the risk of stroke and other cardiovascular events. Maintaining normal thyroid hormone levels through careful monitoring and adjustment of medication is crucial to reducing these risks. Further studies are needed to clarify the complex relationship between thyroid hormones and stroke risk, especially in patients with hypothyroidism.

Thyroid hormone abnormalities and bulbar weakness

Hyperthyroidism and hypothyroidism are two common types of thyroid disease. Thyroid hormone abnormalities can cause bulbar weakness and dysarthria, although this is rare. In such cases, the patient may experience acute bulbar weakness, dysarthria, and oropharyngeal dysphagia.

Acute bulbar weakness is a common symptom of a cerebrovascular accident (CVA) or transient ischemic attack (TIA). However, it is important to consider other potential causes, such as endocrinopathies, which include thyroid disease. These disorders are referred to as "stroke mimics" because they present with features that imitate an acute vascular event.

In a literature review by Chiu et al. in 2004, it was found that severe thyrotoxicosis and thyroid storm rarely precipitated dysarthria and dysphagia. However, patients with thyrotoxicosis usually have some degree of thyrotoxic myopathy or neuropathy before developing dysarthria. The associated myopathy has been documented in the proximal limbs and improves with the management of thyroid dysfunction.

In cases of acute bulbar weakness suspected to be caused by thyroid hormone abnormalities, treatment of the underlying thyroid condition can result in rapid improvement of symptoms. For example, in a case study of a 73-year-old female with acute bulbar weakness, dysarthria, and dysphagia, adjusting her anti-hyperthyroid medications led to a rapid improvement in her symptoms within 48 hours.

Therefore, while thyroid hormone abnormalities are a rare cause of bulbar weakness, prompt diagnosis and treatment can lead to a rapid resolution of symptoms.

Frequently asked questions