Cyclic medical disorders are those that recur in a pattern. The cause of the periodicity can be difficult to define but may include the light-dark cycle, eating patterns, work- or school-related stress, natural refractory period, or hormonal changes. With respect to hormonal changes, catamenial epilepsy, defined as seizures that occur in association with the menses, is of particular interest. Although many factors can precipitate seizures, 60 to 70percnt; of patients with epilepsy (depending on the type of seizure) have a pattern of occurrence that relates to time of day. In addition, a significant proportion of women with seizures experience an exacerbation of their condition in the premenstrual and/or perimenstrual time period.There are several hypotheses about the cause of catamenial epilepsy. In animal studies, estradiol has been shown to increase neuronal excitability and, thus, to lower the seizure threshold. Progesterone has the opposite effect and reduces the rate of neuronal firing. Seizures may be precipitated by changes in the ratio of estrogen to progesterone. Indirect effects of estrogen also may play a role, for example, water retention or edema, faster clearance of anticonvulsants, and changes in serum calcium levels. Improved control of catamenial epilepsy has been observed with a number of therapies that recognize the importance of hormones in the occurrence of seizures: oral progesterone, danazol, clomiphene, progesterone suppositories, medroxyprogesterone, and even oophorectomy. In catamenial epilepsy, neither the specific mechanism nor the optimal therapy have been defined clearly.
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