Abstracts

Rationale: Posterior rhythmic delta activity (PRDA) is a non-specific interictal EEG finding characterized by trains of monomorphic delta waveforms over the posterior head regions, reported in children with generalized absence epilepsy. PRDA is underrecognized and often misinterpreted as a pathological focal finding or epileptiform. This study determined the prevalence of PRDA among children with absence epilepsy and evaluated other associated EEG and epilepsy features. Methods: Children with absence epilepsy with EEGs performed at the Mayo Clinic in Rochester, MN between January 2003 and February 2013 were identified from the EEG database. Patients with epileptic encephalopathy syndromes such as Lennox-Gastaut syndrome were excluded. Seizure history, response to treatment, and EEG reports were reviewed. All EEGs with reported delta slowing were re-reviewed by two board-certified clinical neurophysiologists blinded to clinical history. The presence of PRDA was defined by consensus. Associations between variables were assessed using Chi-Square or Fisher's exact test for categorical values and Wilcoxon rank sum test for continuous variables. Results: A total of 276 EEGs were obtained from 103 children with absence epilepsy (male 43.7%; mean age seizure onset 6.7 years). Epilepsy syndromes included 37 childhood absence epilepsy, 14 juvenile absence epilepsy, 3 juvenile myoclonic epilepsy, 7 myoclonic absence epilepsy, 1 myoclonic astatic epilepsy, and 40 unclassified. PRDA was found in 30/276 EEGs (10.9%) from 20/103 patients (19.4%). Among those records with PRDA, generalized epileptiform discharges were present in 29/30 studies (3 Hz spike and wave activity 31%, generalized atypical spike and wave activity 44.8%, and other epileptiform findings 24.2%). In 35% of patients with PRDA, this finding was not present on the first EEG, but appeared on subsequent EEGs. Comparing EEGs with and without PRDA, PRDA was seen at a younger age (8.3 years vs. 10.9 years, p=0.0013). No correlation was seen between the presence of PRDA and recorded absence seizures, augmentation response to hyperventilation or presence of photoparoxysmal response. Of the EEGs with PRDA, 6 were identified as PRDA, 6 as occipital rhythmic delta activity, 5 as focal onset seizure followed by secondary generalization, and 13 as nonspecific focal delta slowing. Comparing patients with and without PRDA, no difference was found between the number of medication trials, use of dietary therapy for epilepsy, family history of epilepsy, or seizure free outcome at last follow-up (mean duration of follow-up 2.72 years, range 0-10 years ). Conclusions: PRDA is an underrecognized EEG finding seen in about 20% of children with absence epilepsy. Misinterpretation of this non-specific EEG finding may lead to lead to an incorrect diagnosis and inappropriate management.