Abstracts

Rationale: Childhood absence epilepsy (CAE) is common, comprising 8-17% of childhood epilepsy. CAE typically has a good prognosis, but a minority of patients have treatment resistant seizures. There are no reliable predictors for treatment resistance. The primary object of this study was to determine the incidence of treatment resistant CAE in patients followed through a tertiary pediatric centre. The secondary objective was to examine clinical and EEG features for predictors of treatment resistance.Methods: Clinical charts of patients with CAE who presented to the neurology clinic at BCCH between July 2001 March 2013 with a minimum 1 year follow-up were retrospectively reviewed. The diagnosis of CAE was based on the features proposed by the ILAE. Exclusion criteria were: i) myoclonic seizures, eyelid/perioral myoclonia, ii) afebrile seizures prior to onset of absence seizures, iii) generalized tonic clonic (GTC) seizures during the active stage of absence seizures, iv) absence seizures known or suspected to be symptomatic, iv) moderately to severely abnormal EEG background. Treatment-resistant epilepsy was defined as failure to achieve seizure freedom following 2 appropriate antiepileptic drugs (AED). Patients were included in one of two groups: treatment responders or treatment resistant. The demographic, clinical and EEG features of these two groups were compared to determine whether specific factors predict those who would develop treatment-resistant CAE.Results: 116 patients were included in the study. Mean age of absence seizure onset was 5.7 years (1-10 years). The most commonly used first line AEDs were ethosuximide (58%) and valproic acid (36%). 85% of patients responded to ethosuximide and 60% responded to valproic acid as first line treatment. At most recent follow-up, 27 (23%) patients were treatment resistant. Patients under the age of 4 years (n=21) at clinical onset were significantly more like to be treatment resistant, p=0.007. 57% of patients with seizure onset under the age of 4 years were treatment resistant vs 18% of those > 4 years. No difference was seen with respect to gender, history of febrile seizures, family history of epilepsy, or EEG findings (focal discharges, photoparoxysmal response). Eight patients had GTC > 1 year after absence onset. None had absence seizure beginning before 4 years of age. 17/27 (63%) patients with treatment resistant epilepsy eventually become seizure free after further AEDs (3-7 total) or the ketogenic diet.Conclusions: This study supports that treatment resistant seizures in CAE is not uncommon. Clinically it is difficult to predict who will develop treatment resistant epilepsy. Children with onset of absence seizure prior to the age 4 have a higher risk of treatment resistance. Most children eventually became seizure free. Further studies are needed to determine if there are genetic factors that contribute to treatment resistant CAE.