Validation of the phenomenon of regression of seizure frequency in epilepsy.

A phenomenon known as regression of seizure frequency toward the median was observed in a previous clinical study performed in patients with partial seizures. Regression of seizure frequency is a situation in which patients with a frequency of seizures above the median value for the group during an initial period have a tendency to have frequency of seizures decrease during a subsequent period, and other patients with a lower frequency of seizures during the initial period increase their frequency during a subsequent period. To investigate this further, eight published sets of clinical data obtained in epileptic patients with various seizure types were identified by a literature search. Three separate analyses were conducted for each data set. All three analyses clearly demonstrated that regression to the median was present in the studies evaluated. It was concluded that this phenomenon is a real effect in epilepsy and occurs in patients with a wide variety of seizure types. The implication of this phenomenon for physicians treating epileptic patients is that there is value in establishing pattern of seizure frequency for individual patients. This information can be used in assessing those patients whose seizure frequency has increased. The implications of this phenomenon for designing and evaluating antiepileptic drug studies are also discussed.