Abstracts

The rate of becoming seizure free (SF) in established epilepsy is unknown. It is often assumed that SF is unlikely to be achieved once epilepsy is established. An important principle of treatment is that seizures respond soon after an intervention or not at all and that there is a very low background rate of becoming SF that continues even if the intervention is ineffective. We hypothesized (incorrectly) that most patients would become SF at the time of an intervention and then would become SF at a constant very low rate afterward., Standardized data were prospectively collected by epileptologists from patients in the UVA Epilepsy Clinic from April 1998 to November 2004. Data were acquired directly from patients and medical records, and refined, cleaned, and updated at each clinic visit. Analysis was limited to subjects with definite epilepsy [gt]5 years old with 3 or more SZ frequency entries to construct SZ frequency curves. Frequency of each SZ type was collected. For each subject, monthly SZ frequency was plotted over time throughout the study period. SF was defined as a total frequency of 0 for at least 6 mo. Duration of SF was defined by the interval between an intervention (surgery, adding a drug, increasing a drug dose, or other) and the last seizure., From 1638 subjects, 988 had 3 or more SZ frequency entries. 231 were excluded because SF was present from the first entry. Therefore, 757 had active seizures at entry to the study and represented the population that could become SF. Of these, 32% (243) became SF and 68% (514) continued to have seizures. Prior to becoming SF, 34% (84) had a history of SF so that a 6 month interval of SF may not be different from their baseline. However, 50% (121) had a high baseline SZ frequency of [gt]1/mo while only 16% (38) had SZ frequency of [lt]1/mo. suggesting that SF was not due to low baseline SZ frequency. SF developed at the onset of an intervention in 54%, as expected. a cumulative plot of SF over time revealed a significant minority (25%) became SF over the next 24 mo., a rate of 13%/year. The rate of SF subsequently flattened after 24 mo. to a new baseline rate of only about 1-2% per year., A surprisingly significant minority of patients will become SF in the 2 years after the last intervention, suggesting it may take months for therapy to become effective in some situations. This suggests there are brain changes that occur over long durations, possibly in response to therapy. The low rate of SF subsequent to 2 years after an intervention is likely the baseline rate of SF in epilepsy since it occurred without any recent intervention.[figure1], (Supported by University of Virginia.)