title: Triphasic waves versus nonconvulsive status epilepticus: EEG distinction.
abstract: BACKGROUND
  Triphasic waves (TWs) and generalized nonconvulsive status epilepticus (GNCSE) share morphological features that may create diagnostic ambiguity.
  
  
  OBJECTIVE
  To describe electroencephalographic differences between TWs and GNCSE.
  
  
  METHODS
  We retrospectively compared the electroencephalograms (EEGs) of two groups of patients presenting with decreased level of consciousness; those with TWs associated with metabolic encephalopathy and those with GNCSE. We studied the following: demographics, etiology and EEG morphological features. All EEGs were classified blindly (TWs or GNCSE) by two expert EEGers. Agreement between experts and concordance with clinical diagnosis were measured.
  
  
  RESULTS
  We analysed 87 EEGs (71 patients) with TWs and 27 EEGs (13 patients) with GNCSE. Agreement between experts and concordance with clinical diagnosis were excellent. When compared to TWs, epileptiform discharges associated with GNCSE had a higher frequency (mean=2.4Hz vs 1.8Hz) (p<0.001), a shorter duration of phase one (p=0.001), extra-spikes components (69% vs 0%) (p<0.001) and less generalized background slowing (15.1% vs 91.1%) (p<0.001). Amplitude predominance of phase two was common with TWs (40.8% vs 0%) (p=0.01). Lag of phase two was absent in all cases of GNCSE but present in 40.8% of patients with TWs. Noxious or auditory stimulation frequently increased the TWs (51%) while it had no effect on the epileptiform pattern (p=0.008).
  
  
  CONCLUSIONS
  Certain EEG morphological criteria and the response to stimulation are very helpful in distinguishing TWs from GNCSE.
authors.affiliation: Department of Neurology, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada.
authors.forename: Jean-Martin
authors.initials: JM
authors.lastname: Boulanger
authors.forename: Charles
authors.initials: C
authors.lastname: Deacon
authors.forename: Diane
authors.initials: D
authors.lastname: Lécuyer
authors.forename: Sylvie
authors.initials: S
authors.lastname: Gosselin
authors.forename: Jean
authors.initials: J
authors.lastname: Reiher
mesh_terms: D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001928:Brain Diseases, Metabolic / Q000175:diagnosis / Q000503:physiopathology; D002540:Cerebral Cortex / Q000503:physiopathology*; D003937:Diagnosis, Differential; D004569:Electroencephalography / Q000379:methods* / Q000592:standards; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D010812:Physical Stimulation; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D013226:Status Epilepticus / Q000175:diagnosis* / Q000503:physiopathology*