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Can Hypothyroidism Cause Seizures?

Learn how your thyroid hormones can impact brain function.
Can Hypothyroidism Cause Seizures?
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Even though the thyroid is often overlooked, its hormones affect every cell in the body, meaning that your entire body can feel the effects when something isn't right. Even your brain is susceptible to thyroid hormone changes. Here, we look at how low thyroid levels can contribute to seizure activity.


What is hypothyroidism?

Hypothyroidism is when the thyroid gland does not produce enough thyroid hormone to support the body's metabolic needs. As the metabolic powerhouse of the body, the thyroid is responsible for making hormones that tell cells how much energy to use and when to use it. 

When there is insufficient thyroid hormone in the body, cells assume they are supposed to conserve energy. Therefore, people with hypothyroidism find their body systems slow down. For example, your digestive tract can become sluggish, leading to constipation, and you might always feel tired.

Other symptoms of hypothyroidism include:

  • Muscle and joint pain
  • Slowed heart rate
  • Cold intolerance
  • Lethargy
  • Dry skin, brittle nails, and thinning hair
  • Depression
  • Irregular menstrual periods

There are two classes of hypothyroidism: primary and secondary

In primary hypothyroidism, the thyroid gland cannot produce thyroid hormone because of a problem with the gland itself. The most common cause of primary hypothyroidism is Hashimoto's, an autoimmune condition where the immune system attacks the thyroid gland. However, it may also be caused by surgery or medications that alter thyroid function.

Secondary hypothyroidism is usually due to a problem with the pituitary gland. This master gland in the brain tells the thyroid how much hormone to produce by releasing thyroid-stimulating hormone (TSH). A pituitary tumor or damage to this gland can affect its function.

Hypothyroidism is rarely life-threatening, but severe hypothyroidism can lead to myxedema coma. In this state, thyroid hormone levels fall so low that organ systems begin to shut down. Cognitive impairment and even seizures can accompany this critical state.


What are seizures?

Seizures occur when uncontrolled electrical impulses are firing in the brain, which can affect a person's level of consciousness and alter their brain function. Seizures vary in severity and frequency. Some seizures result in a temporary loss of awareness, like you are in a dream, whereas others can take over your whole body causing muscles to weaken or become tonic. 

Sometimes, people randomly have a seizure due to a complication like a high fever or infection. However, if occurring more frequently and no root cause is known, a person may be diagnosed with epilepsy.  Seizures can also be a side effect of other health conditions such as diabetes, hypothyroidism, autoimmune disorders, and low sodium (hyponatremia).


How thyroid hormones influence seizure activity?

Thyroid hormones may play a role in epileptic seizures, as they are essential for normal central nervous system development and function. We know this because people born with congenital hypothyroidism (hypothyroidism at birth) are at a heightened risk for cognitive impairments. And people with even mild or subclinical hypothyroidism can suffer from some changes in cognition, including slowed thought processes, brain fog, and even mood changes. 

While we still do not fully know the underlying mechanisms for how thyroid hormones can potentially influence seizures, we know thyroid hormones can:

  • Bind to nuclear receptors
  • Modulate gene expression
  • Influence neural migration and differentiation.

They also have inhibitory and excitatory effects on neurons, which may contribute to seizure activity in the brain. Some studies postulate that thyroid dysfunction may contribute to epilepsy, although more research is needed to confirm or deny this hypothesis. 

Thyroid-associated antibodies (like TPO antibodies) may also contribute to seizures in people with Hashimoto's encephalopathy, a rare disease where an abnormal immune response triggers how the brain works. Despite its name, the relationship between Hashimoto's encephalopathy and Hashimoto's thyroiditis (autoimmune hypothyroidism) is not well understood. However, we do know the two conditions are associated. 

Are people with hypothyroidism at risk for seizures?

While there is a relationship between thyroid hormones and seizures, you should know that people with hypothyroidism do not usually develop seizures. Instead, people with epilepsy often also have an imbalance in their thyroid hormone levels.

However, in rare cases where a person has severe hypothyroidism that manifests into a myxedema coma, it can cause seizures, most likely caused by hyponatremia (low sodium). 

A myxedema coma is a life-threatening state that requires immediate medical attention. People with this complication typically end up in the intensive care unit and may even require critical interventions like mechanical ventilation.

It is not just severely low thyroid hormones that lead to myxedema coma. Traumatic events on the body can activate it, such as burns, infection, certain medications, hypoglycemia, surgery, and physical injury.

Although rare, it is important to know the signs of myxedema coma, which include:

  • Altered mental function
  • Low blood pressure
  • Slow heart rate
  • Delayed reflexes
  • Hyperventilation
  • Hypothermia
  • Myxedema face (the face becomes swollen)
  • Non-pitting edema


Caring for your thyroid (and the whole body)

People with an underactive thyroid can experience different physical and mental symptoms associated with low thyroid hormones. Therefore, keeping your thyroid hormones at a healthy level is crucial. 

Most people require thyroid hormone replacement to correct low levels. Lifestyle changes can improve symptoms. You will need a complete thyroid function test assessing your TSH, free T4, free T3, and TPO antibodies to check your thyroid function. Then, based on your medical history, thyroid test results, and symptoms, you and your doctor will decide the best plan. 

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Mary Shomon

Patient Advocate

Mary Shomon is an internationally-recognized writer, award-winning patient advocate, health coach, and activist, and the New York Times bestselling author of 15 books on health and wellness, including the Thyroid Diet Revolution and Living Well With Hypothyroidism. On social media, Mary empowers and informs a community of more than a quarter million patients who have thyroid and hormonal health challenges.

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