Many women who have epilepsy know they are more likely to have seizures just before or at the start of their monthly periods. This gender-specific difference in epilepsy has been documented in medical records since 1885. Up to 70 percent of female epilepsy patients believe their periods exacerbate their seizures, although some studies show the actual number of women experiencing this type of seizure increase is much lower.
A seizure is an abnormal surge of electrical activity in the brain. Seizures can last a few seconds or several minutes and can result in convulsions or uncontrolled movement of the lips, arms, or legs. Epilepsy with seizures that are more common at certain times during the menstrual cycle is known as catamenial epilepsy. Although rare, some women with this type of epilepsy only have seizures when they have their periods. The more common situation is women who have seizures throughout the month but have more seizures with their periods, or women whose seizures are well controlled with medications at all times of the month except when they are menstruating.
Menstruation in women is controlled by hormones, which are chemical messengers used by the brain to coordinate activities throughout the body. In particular, the hormones estrogen and progesterone are known to be active in the menstrual cycle and to effect catamenial seizures. Estrogen, especially in the form estradiol, is known to promote seizures in women with epilepsy. Progesterone acts to reduce or limit seizure activity.
During the menstrual cycle, estrogen levels increase mid-month at the time of ovulation which is when an egg is released. This is one key time when seizures may increase. In most women, estrogen levels then return to normal. However, some women with abnormal cycles of ovulation may have higher estrogen levels for the rest of the month until the start of their periods. Another possible cause of increased seizures is the monthly dip in progesterone levels just before the start of menstruation each month. Researchers believe the imbalance between estrogen and progesterone (either excess estrogen or too little progesterone) is the key that allows catamenial seizures to occur.
In addition, studies show that some medications to control seizure activity may also be effected by hormone levels. For example, the anticonvulsant Phenytoin may be effective for a shorter time just prior to a woman’s period. Studies have shown that the half-life of this drug decreases from 19 hours to 13 hours just prior to some women’s periods. The half-life of a drug is the amount of time it takes for half the active ingredient to be metabolized out of the bloodstream.
Some women have found that certain types of birth control also interact with their anticonvulsant medications. For some, their seizure drugs cause birth control to be less effective which can increase the risk of getting pregnant. Others have found that using certain types of birth control such as IUDs that contain low levels of hormones can help reduce their seizures around the time of their periods.
If you have questions about how hormones may be affecting your epilepsy or if you suspect your medication is less effective at certain times of the month, talk to your health care provider to see if different medications or different doses could help.
Sources:
Medscape
Epilepsy.com
Epilepsy Foundation
Merck Manuals
Reviewed May 31, 2011
Edited by Alison Stanton