Intractable Epilepsy: Relapsing, Remitting, or Progressive?
Authors: Herman Susan 
Published: October 2010

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.