From the Research
Subclinical hypothyroidism is unlikely to directly cause seizures in most patients. Subclinical hypothyroidism is defined by mildly elevated TSH levels with normal free T4 levels, and typically produces minimal or no symptoms. While severe hypothyroidism (myxedema) can potentially trigger seizures due to significant metabolic disturbances, the subtle hormonal changes in subclinical hypothyroidism generally aren't severe enough to lower the seizure threshold. However, if a patient has a pre-existing seizure disorder, even mild thyroid dysfunction might theoretically affect seizure control in some individuals. Thyroid hormones play important roles in neuronal development and function, influencing neurotransmitter systems and brain metabolism, as discussed in a study on the neurological and cognitive effects of hypothyroidism in patients with epilepsy 1.
Some key points to consider:
- Subclinical hypothyroidism may be associated with cognitive dysfunction, mood disturbance, and diminished response to standard psychiatric treatments, but its link to seizures is less clear 2.
- The treatment of subclinical hypothyroidism with levothyroxine is generally not indicated solely for seizure prevention, but might be considered based on other clinical factors and symptoms 3.
- Thyroid hormones have been shown to influence neuronal migration, differentiation, myelination, synaptogenesis, and neurogenesis in developing and adult brains, and their abnormalities may contribute to the pathogenesis of epilepsy 4.
- A case report of thyroxine-induced hypermotor seizure suggests that thyroid hormone replacement therapy can, in rare cases, induce seizures, but this is not directly related to subclinical hypothyroidism itself 5.
In clinical practice, if a patient with subclinical hypothyroidism experiences seizures, other more common causes should be investigated, including electrolyte abnormalities, structural brain lesions, or primary seizure disorders. The most recent and highest quality study on this topic, published in 2025, provides valuable insights into the neurological and cognitive effects of hypothyroidism in patients with epilepsy, but does not establish a direct link between subclinical hypothyroidism and seizures 1. Therefore, treatment of subclinical hypothyroidism with levothyroxine should be based on other clinical factors and symptoms, rather than solely for seizure prevention.