Triphasic Waves Versus Nonconvulsive Status Epilepticus: EEG Distinction

Abstract

The electroencephalogram (EEG) is a very useful tool for the evaluation of patients with altered levels of consciousness and coma. 1,2 It permits one to rule out status epilepticus, confirm a diffuse or focal process and may orient the clinician towards an underlying etiology. Triphasic waves (TWs) on the EEG were described more than five decades ago and are usually attributed to a metabolic encephalopathy. 3,4 The association of TWs with hepatic encephalopathy is well known. In the past, they were thought of as being pathognomonic of hepatic coma. We now know that TWs are associated with a wide variety of disorders (metabolic and non-metabolic) affecting the brain diffusely. 5,6 Triphasic waves are not epileptiform per se and are usually not associated with seizures. The TWs and generalized periodic or continuous epileptiform discharges occurring in generalized nonconvulsive status epilepticus (GNCSE) may share 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. Tous les patients avaient une altération de la conscience. Les caractéristiques suivantes furent analysées: âge, étiologie sous-jacente et plusieurs caractéristiques morphologiques de l'EEG. Tous les EEGs ont été classifiés à l'aveugle (OT ou SEGNC) par deux électroencéphalographistes experts et l'exactitude par rapport au diagnostic clinique a été évaluée de même que la concordance entre les deux experts. Résultats: 87 EEGs (71 patients) avec OT et 27 EEGs (13 patients) avec SEGNC ont été analysés. La concordance entre les experts et l'exacti...

Periodic EEG patterns: importance of their recognition and clinical significance

“…In these situations, some authors recommend the use of benzodiazepines administration to verify the resolution of EEG changes in the cases of nonconvulsive status epilepticus even though thriphasic waves may be abolished by benzodiazepines administration, as demonstrated by Foutain et al 54 . Boulanger et al 55 compared the 87 EEGs of 71 patients with triphasic waves and 27 EEGs of 13 patients with nonconvulsive status epilepticus, and showed that, when compared to triphasic waves, epileptiform discharges associated with nonconvulsive status epilepticus had a higher frequency, a Periodic lateralized epileptiform discharges (PLEDs) in the right hemisphere, predominantly over the frontotemporal regions (A), with some widespread, evolving to generalized periodic epileptiform discharges (GPEDs) (B) in an EEG of a 50-year-old woman with rapidly progressive cognitive impairment, altered mental status and muscle spasms. The clinical picture, the neuroimaging studies, the absence of toxic-metabolic disorders and no improvement with antiepileptic drug allied to the EEG periodic patterns supported the presumptive diagnosis of Creutzfeldt-Jakob disease.…”

A Case of Nonconvulsive Status Epilepticus Presenting with Triphasic Waves

“…[7] Bu iki durumun yönetimi birbirinden farklı olup NKSE'de antiepileptik ilaç-ların kullanımı gerekmekte, metabolik ensefalopatide ise altta yatan etyolojiye yönelik tedaviler uygulanmaktadır. [8] Trifazik dalgaların morfolojik özellikleri NKSE ve metabolik ensefalopati ayırıcı tanısında önemli olabilmektedir. Yapılan çalışmalara göre; metabolik ensefalopatiye özgü trifazik dalgalar bilateral simetrik ve anterior bölgelerde ağırlıklı olarak gözlenmekte, fokal ya da bilateral asimetrik yerleşimli atipik trifazik dalgaların varlığı NKSE'yi akla getirmektedir.…”

Significance of Triphasic Waves in Metabolic Encephalopathy

“…The risk of having GCS ≤ 10 was at least 6 times higher in the patients with triphasic waves than those without triphasic waves, and also the risk of having acute symptomatic seizures was at wider angle between the second and third phases of triphasic waves. [12][13][14] In addition, GPEDs can have phase reversals and polyspikes, whereas triphasic waves have fewer phase reversals and polyspikes. 12 Response of waveforms to stimulation is another useful way to discriminate triphsic waves and GPEDs.…”

“…Triphasic waves increase with stimulation such as auditory, visual, and noxious method, whereas GPEDs are not influenced by external stimuli. 13 The differences can be also clarified on the clinical ground. In contrast to GPEDs, patients with triphasic waves usually do not recover mental deterioration after administration of benzodiazepine.…”