Seizure Remission and Relapse in Adults with Intractable Epilepsy: A Cohort Study.  Choi H, Heiman G, Pandis D, Cantero J, Resor SR, Gilliam FG, Hauser WA. Epilepsia 2008;49(8):1440–1445.  PURPOSE: To investigate the cumulative probabilities of ≥12 month seizure remission and seizure relapse following remission, and to test the associations of clinical characteristics with these two study end points in a prevalence cohort of intractable adult epilepsy patients during medical management. METHODS: A retrospective cohort study of intractable epilepsy patients seen in 2001 at a single center was conducted. Kaplan–Meier analysis was used to estimate the cumulative probabilities of seizure remission and subsequent seizure relapse. Cox proportional hazards models were used to estimate the association (1) between clinical factors and ≥12 month seizure remission and (2) between clinical factors and seizure relapse following remission. RESULTS: One hundred eighty-seven subjects met the eligibility criteria for intractable epilepsy. The estimate of probability of remission was about 4% per year. Seizure remission was temporary for some individuals, as 5 out of 20 subjects with remission ultimately relapsed. No clinical factors predicted the likelihood of achieving ≥12 month seizure remission or subsequent seizure relapse. DISCUSSION: Some people with intractable epilepsy achieve ≥12 month seizure remission during medical treatment. Remission, however, is only temporary for some individuals. We were unable to identify clear predictors for remission.

Quantifying the Response to Antiepileptic Drugs: Effect of Past Treatment History.  Schiller Y, Najjar Y. Neurology 2008;70(1):54–65.  OBJECTIVE: To quantify the response to treatment with antiepileptic drugs (AEDs) as a function of the past treatment history and identify additional prognostic factors for predicting the response to newly administered AED treatments. METHODS: A cohort of 478 consecutive patients who received newly administered AED treatments between January 1999 and December 2004 and were followed prospectively for 1.5 to 7.5 years in a single epilepsy clinic. RESULTS: The response to newly administered AED treatments was highly dependent on the past treatment history. The seizure-free rates decreased from 61.8% for the first AED to 41.7%, 16.6%, and 0% after one, two to five, and six to seven past AEDs proved inefficient. This response curve corresponded to a mono-exponential function with a maximal response of 61.8% and half-decay constant of 1.5 AEDs. Likewise the response curve describing a greater than 50% reduction in seizure frequency corresponded to a mono-exponential function with a maximal response of 85.3% and half-decay constant of two AEDs. Three additional independent prognostic factors for predicting the response to AEDs were identified: type of epilepsy, duration of epilepsy, and number of seizures in the 3 months prior to AED initiation. CONCLUSION: Drug resistance is a graded process that follows a mono-exponential course with a half-decay constant of 1.5 to two antiepileptic drugs (AEDs). Although relative drug-resistant epilepsy can be diagnosed after failure of two past AEDs, absolute drug resistance requires failure of six AEDs, as a significant minority of patients (16.6%) is rendered seizure-free by addition of newly administered AEDs even after failure of two to five past antiepileptic drugs.