Catamenial epilepsy is a gender-specific type of epilepsy in which seizure frequency intensifies during certain phases of the menstrual cycle. An increase in seizures in parallel with the menstrual cycle in some women with epilepsy has been noticed since ancient times.
A recent review article summarized possible mechanisms underlying seizures in catamenial epilepsy and animal models used by scientists to study catamenial epilepsy in the lab. This article comes from the lab of Dr. Reddy who is at the Texas A&M College of Medicine.
Studies suggest that catamenial epilepsy is seen in 10 to 70% of women with epilepsy. Clearly, this range is rather big and is thought to be due to people using inconsistent definitions for catamenial epilepsy.
Traditionally used anti-epileptic drugs typically do not have an effect on seizures in catamenial epilepsy. Hence, it is critical to study this phenomenon in greater detail.
Catamenial epilepsy is identified by charting seizures and menses in a diary. Seizures during each phase of the menstrual cycle are noted, and this is done for at least two menstrual cycles. If a comprehensive review of the seizure / menstruation diary reveals a two-fold increase in seizure frequency during one phase of the menstrual cycle, one can suspect catamenial epilepsy.
Steroid hormones such as estrogen and progesterone circulate throughout the brain and have been shown to have effects on neuronal excitability. Estrogen has been shown to increase seizures, whereas progesterone has anti-seizure effects. Hence, imbalances in estrogen and progesterone levels might lead to seizures, and studying estrogen-progesterone ratio might be a good way to understand this phenomenon. Estrogen and progesterone finely regulate the menstrual cycle, leading to four phases of the cycle: menstrual phase (the time when a woman has her period), follicular phase (when the ovary is getting ready to release an egg), ovulatory phase (when the egg is released), and luteal phase (the time between the egg's release and the start of menstruation).
Catamenial epilepsy is not just one entity, but can occur at any phase of the menstrual cycle, i.e., it can be perimenstrual, periovulatory, or luteal.
Perimenstrual seizures are associated with an increase in seizure frequency during the menstrual phase and arise from a drastic decrease in both progesterone and estrogen levels.
Periovulatory seizures are associated with a high seizure frequency in the ovulatory phase and are attributed to a high estrogen-progesterone ratio. Since estrogen can exacerbate seizures and progesterone (which is an anticonvulsant) levels are low, this phase may be associated with seizures.
Luteal seizures are caused by low levels of progesterone and of neurosteroids (especially one known as allopregnanolone) that are derived from progesterone..