title: When spikes are symmetric, ripples are not: Bilateral spike and wave above 80 Hz in focal and generalized epilepsy.
abstract: OBJECTIVE
  To evaluate scalp ripples distribution in secondary bilateral synchrony as a tool to lateralize the epileptic focus and to differentiate focal from generalized epilepsy.
  
  
  METHODS
  Seventeen EEG recordings with bilateral synchronous discharges of focal (focal group-FG: 10) and generalized (generalized group-GG: 7) epilepsy patients were selected for spikes and ripples marking; the spike-normalized ripple rate was calculated in each hemisphere (right/left - anterior/posterior) and a ripple-dominant hemisphere (the one with the highest rate) was identified. Concordance in FG between the ripple dominant hemisphere and the hemisphere of clinical lateralization was evaluated. The ripple-dominant/ripple-nondominant spike-normalized ripple rate ratio was studied to compare groups.
  
  
  RESULTS
  In FG the hemisphere of clinical lateralization and the ripple-dominant hemisphere were 100% concordant. In GG only 3/7 patients showed ripples (vs 10/10 FG), all with anterior dominance. No difference in hemisphere ripple dominance between groups was found.
  
  
  CONCLUSIONS
  Ripples in secondary bilateral synchrony help to lateralize the epileptic focus but do not help to differentiate between focal and generalized epilepsy. This is the first report of visually identified ripples in idiopathic generalized epilepsy.
  
  
  CONCLUSIONS
  Ripples confirm the clinical lateralization of the epileptic focus in secondary bilateral synchrony but cannot distinguish between focal and generalized epilepsy.
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, QC, Canada; Epilepsy Unit, Careggi Hospital, University of Florence, Florence, Italy. Electronic address: francescapizzo@gmail.com.
authors.forename: Francesca
authors.initials: F
authors.lastname: Pizzo
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, QC, Canada; Department of Clinical Neurophysiology, Hospital Israelita Albert Einstein, São Paulo, Brazil.
authors.forename: Taissa
authors.initials: T
authors.lastname: Ferrari-Marinho
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, QC, Canada.
authors.forename: Mina
authors.initials: M
authors.lastname: Amiri
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, QC, Canada.
authors.forename: Birgit
authors.initials: B
authors.lastname: Frauscher
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, QC, Canada.
authors.forename: Francois
authors.initials: F
authors.lastname: Dubeau
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, QC, Canada.
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004569:Electroencephalography / Q000379:methods* / Q000592:standards; D004828:Epilepsies, Partial / Q000175:diagnosis* / Q000503:physiopathology*; D004829:Epilepsy, Generalized / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013686:Telemetry / Q000379:methods / Q000592:standards; D055815:Young Adult
keywords: Bilateral synchrony; Fast oscillations; Idiopathic generalized epilepsy; Ripple; Scalp EEG