Yes, thyroid disorders can cause seizures through several different pathways. Both an overactive and underactive thyroid can alter brain function enough to trigger seizure activity, and a specific autoimmune condition linked to thyroid antibodies causes seizures in nearly half of affected patients. The connection isn’t always obvious, which is why thyroid-related seizures often go unrecognized at first.
How an Overactive Thyroid Triggers Seizures
Thyroid hormones play a direct role in how brain cells communicate. When your thyroid produces too much hormone, a condition called hyperthyroidism, it increases the excitability of neurons throughout the brain. Think of it as turning up the electrical activity to a point where normal signals can misfire, lowering the threshold at which a seizure occurs.
The most dangerous scenario is thyroid storm, a rare but life-threatening escalation of hyperthyroidism. In a nationwide Japanese survey of mostly adult thyroid storm patients, about 4% experienced seizures. But in children and adolescents, the rate is significantly higher. A literature review of 84 pediatric thyroid storm cases found that 16 of them, roughly 19%, involved seizures. This gap suggests that developing brains may be more vulnerable to the neurological effects of excess thyroid hormone.
How an Underactive Thyroid Triggers Seizures
Severe hypothyroidism can also lead to seizures, though through different mechanisms. When thyroid hormone levels drop very low, the body’s metabolism slows dramatically. In extreme cases this progresses to myxedema crisis, a medical emergency with a high mortality rate.
Several things happen in the brain during myxedema crisis that can spark seizure activity. Low thyroid hormone causes a general depression of brain function. On top of that, severe hypothyroidism often leads to dangerously low sodium levels (hyponatremia) because the body starts retaining too much water, sometimes due to inappropriate release of a hormone that controls fluid balance. Low sodium disrupts the electrical environment brain cells need to function properly. Seizures from low sodium typically occur when levels drop below 120 millimoles per liter, though in the setting of myxedema, seizures can happen at moderately low sodium levels too.
Low blood sugar, reduced oxygen levels, and decreased blood flow to the brain can all pile on in severe hypothyroidism, each one independently capable of worsening seizure risk. The combination makes myxedema crisis with seizures particularly dangerous.
Hashimoto’s Encephalopathy: The Autoimmune Connection
Perhaps the most striking link between thyroid disease and seizures comes from a condition called Hashimoto’s encephalopathy, also known as steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT). This is an immune-mediated disorder where the presence of anti-thyroid antibodies is associated with inflammation affecting the brain.
Seizures are the single most common symptom. In a review of 251 patients with SREAT, 47% experienced convulsions. Other symptoms included confusion (46%), memory problems (43%), speech difficulties (37%), and walking problems (27%). Some patients developed hallucinations or psychiatric symptoms that initially looked like a primary mental health condition.
What makes this condition tricky is that patients often have normal or only mildly abnormal thyroid hormone levels. The problem isn’t the thyroid hormones themselves but the autoimmune process. Roughly two-thirds of patients test positive for both anti-TPO and anti-thyroglobulin antibodies, while about a third have only anti-TPO antibodies. Interestingly, researchers have found no direct correlation between how high the antibody levels are and how severe the symptoms become. The antibodies appear to be a marker of the disease rather than its direct cause.
SREAT is a diagnosis of exclusion, meaning doctors arrive at it by ruling out infections, tumors, and other causes of brain inflammation first. EEG testing shows abnormalities in about 82% of patients, most commonly a diffuse slowing pattern consistent with encephalopathy. MRI scans are typically normal or show only nonspecific changes, which can make the diagnosis easy to miss.
Why Standard Seizure Medications Often Aren’t Enough
Seizure disorders are found in approximately two-thirds of patients diagnosed with Hashimoto’s encephalopathy, and anti-seizure medications alone are usually not effective. The seizures stem from an immune process, so the treatment needs to target immunity. Corticosteroids are the first-line treatment, and the response is often dramatic. In the 251-patient review, 91% of patients showed complete or partial neurological improvement, typically within the first year. However, about 16% of patients experienced at least one relapse, with relapses more common in those who initially presented with coma.
Seizures After Thyroid Surgery
There’s one more pathway worth knowing about. After a total thyroidectomy, the parathyroid glands (tiny glands located right next to or behind the thyroid) can be damaged or inadvertently removed. These glands control calcium levels in the blood. When they stop working properly, calcium drops, and low calcium is a well-known seizure trigger.
This complication can show up immediately after surgery or, in rare cases, years later. One documented case involved a woman who developed seizures from severe low calcium roughly 25 years after her thyroidectomy. The seizures resolved once calcium levels were restored. If you’ve had thyroid surgery and experience muscle cramps, tingling in your fingers or around your mouth, or unexplained seizures, low calcium from parathyroid damage is something to consider.
Seizure Medications Can Affect Your Thyroid
The relationship between thyroid disease and seizures runs in both directions. If you’re already taking seizure medications, some of them can alter your thyroid hormone levels. Older, conventional drugs like phenytoin, carbamazepine, and phenobarbital speed up how the liver breaks down thyroid hormones. This leads to lower free T4 levels and higher TSH levels, essentially pushing the body toward a hypothyroid state.
The mechanism involves liver enzymes that metabolize thyroid hormones faster than normal. Carbamazepine may also interfere with how the thyroid gland absorbs iodine, adding another layer to the disruption. Newer seizure medications like levetiracetam do not appear to have the same effect on thyroid function. This interaction matters because if you’re being treated for both epilepsy and a thyroid condition, changes in one medication can throw off the other. Your thyroid hormone doses may need adjustment if seizure medications are started or switched.
Recognizing Thyroid-Related Seizures
Thyroid-related seizures can look identical to seizures from any other cause. They can be generalized tonic-clonic (full-body convulsions), focal (affecting one part of the body), or even present as subtle episodes of confusion or staring. The key clue is context: unexplained seizures in someone with known thyroid disease, a family history of autoimmune conditions, or other symptoms like unexpected weight changes, fatigue, heat intolerance, or brain fog.
A basic thyroid panel measuring TSH, free T4, and T3 can identify overt hyper- or hypothyroidism. Normal TSH falls between roughly 0.4 and 4.2 mU/L, though ranges vary slightly between labs. But because Hashimoto’s encephalopathy can occur even with normal thyroid hormone levels, doctors sometimes need to check anti-TPO and anti-thyroglobulin antibodies separately, especially when seizures have no other clear explanation. In one reported SREAT case, TPO antibodies exceeded 600 IU/mL (normal is below 35) and thyroglobulin antibodies topped 2,250 IU/mL (normal is below 10).
The takeaway is that thyroid problems cause seizures through multiple routes: direct effects of too much or too little thyroid hormone on brain cells, secondary metabolic disruptions like low sodium or low calcium, and autoimmune inflammation of the brain. Each pathway has a different treatment, which is why identifying the underlying thyroid connection matters so much for getting seizures under control.