Stimulus-induced arousal with transient electroencephalographic improvement distinguishes nonictal from ictal generalized periodic discharges.

In the case of suspicion of nonconvulsive status epilepticus (NCSE), reactivity on electroencephalograms (EEGs) can provide valuable diagnostic information. Reactivity refers to responses to auditory or somatosensory stimulation, with changes in amplitude and frequency of background activity. Because of self-perpetuating processes and the failure of self-terminating mechanisms, status epilepticus is unlikely to cease when patients spontaneously move, and it cannot typically be stopped by external stimulation (i.e., auditory and tactile stimuli). The defining EEG characteristic of absence status epilepticus is the presence of bilateral, synchronous, symmetric, rhythmic paroxysmal activity that shows little or no reactivity to sensory stimulation. On the other hand, in metabolic/toxic or multifactorial encephalopathies, triphasic waves (TWs) are influenced by the level of vigilance. TWs may be transiently abolished when patients increase their level of alertness from a drowsy/lethargic state to a state of wakefulness. This reactivity is only observed when patients can be aroused by a somatosensory or auditory stimulus. This reactivity tends to disappear with increasing severity of the disease and in comatose patients. In patients without preexisting developmental and epileptic encephalopathy, this pattern of stimulus-induced wakefulness with transient improvement of the EEG is a major criterion in determining that the EEG patterns are not ictal. This criterion of reactivity on EEGs, beyond the classical clinical/EEG criteria of NCSE (Salzburg criteria), should now be systematically added.

EEG and acute confusional state at the emergency department.

OBJECTIVES: Acute confusional state (ACS) is a common cause of admission to the emergency department (ED). It can be related to numerous etiologies. Electroencephalography (EEG) can show specific abnormalities in cases of non-convulsive status epilepticus (NCSE), or metabolic or toxic encephalopathy. However, up to 80% of patients with a final diagnosis of NCSE have an ACS initially attributed to another cause. The exact place of EEG in the diagnostic work-up remains unclear. METHODS: Data of consecutive patients admitted to the ED for an ACS in a two-year period and who were referred for an EEG were collected. The initial working diagnosis was based on medical history, clinical, biological and imaging investigations allowing classification into four diagnostic categories. Comparison to the final diagnosis was performed after EEG recordings (and sometimes additional tests) were performed, which allowed the reclassification of some patients from one category to another. RESULTS: Seventy-five patients (mean age: 71.1 years) were included with the following suspected diagnoses: seizures for 8 (11%), encephalopathy for 14 (19%), other cause for 34 (45%) and unknown for 19 (25%). EEG was recorded after a mean of 1.5 days after symptom onset, and resulted in the reclassification of patients as follows: seizure for 15 (20%), encephalopathy for 15 (20%), other cause for 29 (39%) and unknown cause for 16 (21%). Moreover, ongoing epileptic activity (NCSE or seizure) and interictal epileptiform activity were found in eight (11%) patients initially diagnosed in another category. DISCUSSION: In our cohort, EEG was a key examination in the management strategy of ACS in 11% of patients admitted to the ED. It resulted in a diagnosis of epilepsy in these patients admitted with unusual confounding presentations.

Determining ICU EEG periodic patterns and why it matters.

Historically, periodic EEG patterns were described as any pattern with stereotyped paroxysmal complexes occurring at regular intervals, i.e., the period (T). T is the sum of the duration of the waveform (t1) and, eventually, the duration of the interval between two consecutive waves (t2). The American Clinical Neurophysiology Society introduced the concept of a clearly discernible inter-discharge interval between consecutive waveforms (i.e., t2). As this definition was not applied to what have previously been termed triphasic waves and in some cases of lateralized periodic discharges, we propose reconsideration of terminology that includes historical use of definitions. This will allow the development and usage of the concept for periodic EEG patterns as any runs of stereotyped paroxysmal waveforms separated by nearly identical intervals and prolonged repetitive complexes on the EEG. Prolonged expression means EEG is recorded for a sufficient period of time to prove that the pattern is repetitive, thus resulting in a monomorphic/monotonous pattern. More important than the inter-discharge interval (t2), periodic EEG patterns occur at time regular intervals (T). As a result, periodic EEG activity should be considered along a continuum and not the opposite of rhythmic EEG activity where no interval activity exists between consecutive waveforms.

Triphasic waves and brain atrophy in patients with acute encephalopathy.

Introduction: Triphasic waves (TW) constitute an electroencephalographic pattern associated with certain kinds of encephalopathy. Brain atrophy may be a predisposing factor linked with TW. Objective: To compare the degree of brain atrophy and white matter disease between patients with acute encephalopathy with and without TW. Methods: A retrospective observational study including adult patients with encephalopathy, with and without TW, hospitalized between 2016 and 2017. The degree of brain atrophy and white matter lesion were defined using the Global Cortical Atrophy and Age Related White Matter Changes (ARWMC) scales, respectively. Scores were compared between groups. Mortality rates were registered. Results: Sixteen patients with TW were identified matched by age and sex with 30 patients without TW. The mean age was 80 years in the TW group. Women represented 87.5%. Multifactorial encephalopathy was the most frequent diagnosis followed by metabolic encephalopathy. Patients with TW had more brain atrophy (10.43 vs 6.9, p= 0.03). Mean ARWMC was 9.43±6.5 and 8.5 ±7.89 in patients with and without TW respectively (p= 0.5). Mortality rate was higher in the TW group (31.25 vs 6.66% p= 0.02). Conclusions: Patients with acute encephalopathy and TW had higher degree of cerebral atrophy. It is possible that this structural alteration predisposes to the appearance of TW. There was no significant difference in white matter lesion degree. The mortality of the TW group was high, so future studies are necessary to determine their prognostic value.

Introducción: Las ondas trifásicas (OT) constituyen un patrón electroencefalográfico asociado con diversas encefalopatías. La atrofia cerebral podría predisponer a su aparición. Objetivo: Comparar el grado de atrofia cerebral y de lesión de sustancia blanca en pacientes con encefalopatía aguda con y sin OT. Métodos: Estudio observacional retrospectivo, incluyó pacientes adultos con encefalopatía aguda con y sin OT internados entre 2016 y 2019. El grado de atrofia cerebral y de lesión de sustancia blanca se definieron según las escalas Global Cortical Atrophy y Age Related White Matter Changes (ARWMC), respectivamente. Se compararon los puntajes entre grupos. Se registró la mortalidad. Resultados: Se identificaron 16 pacientes con OT y 30 sin OT pareados según edad y sexo. La edad promedio del grupo con OT fue 80 años. El 87.5% fueron mujeres. La encefalopatía multifactorial fue el diagnóstico más frecuente seguido de la encefalopatía metabólica. El grado de atrofia fue mayor en pacientes con OT (10.43 vs 6.9, p= 0.03). El puntaje ARWMC fue 9.43 ±6.5 y 8.5 ±7.89 en pacientes con y sin OT respectivamente (p= 0.5). La mortalidad fue mayor en el grupo con OT (31.25 vs 6.66% p= 0.02). Conclusiones: Pacientes con encefalopatía aguda y OT tuvieron mayor grado de atrofia cerebral. Dicha alteración estructural podría relacionarse con la aparición de OT. No hubo diferencias significativas en el grado de lesión de sustancia blanca. La mortalidad del grupo con OT fue elevada. Son necesarios estudios para determinar su valor pronóstico.

Triphasic waves and brain atrophy in patients with acute encephalopathy / Ondas trifásicas y atrofia cerebral en pacientes con encefalopatía aguda

Abstract Introduction: Triphasic waves (TW) constitute an electroencephalographic pattern associated with certain kinds of encephalopathy. Brain atrophy may be a predisposing factor linked with TW. Objective: To compare the degree of brain atrophy and white matter disease between patients with acute encephalopathy with and without TW. Methods: A retrospective observational study including adult patients with encephalopathy, with and without TW, hospitalized between 2016 and 2017. The degree of brain atrophy and white matter lesion were defined using the Global Cortical Atrophy and Age Related White Matter Changes (ARWMC) scales, respectively. Scores were compared between groups. Mortality rates were registered. Results: Sixteen patients with TW were identified matched by age and sex with 30 patients without TW. The mean age was 80 years in the TW group. Women represented 87.5%. Multifactorial encephalopathy was the most frequent diagnosis followed by metabolic encephalopathy. Patients with TW had more brain atrophy (10.43 vs 6.9, p= 0.03). Mean ARWMC was 9.43±6.5 and 8.5 ±7.89 in patients with and without TW respectively (p= 0.5). Mortality rate was higher in the TW group (31.25 vs 6.66% p= 0.02). Conclusions: Patients with acute encephalopathy and TW had higher degree of cerebral atrophy. It is possible that this structural alteration predisposes to the appearance of TW. There was no significant difference in white matter lesion degree. The mortality of the TW group was high, so future studies are necessary to determine their prognostic value.

Resumen Introducción: Las ondas trifásicas (OT) constituyen un patrón electroencefalográfico asociado con diversas encefalopatías. La atrofia cerebral podría predisponer a su aparición. Objetivo: Comparar el grado de atrofia cerebral y de lesión de sustancia blanca en pacientes con encefalopatía aguda con y sin OT. Métodos: Estudio observacional retrospectivo, incluyó pacientes adultos con encefalopatía aguda con y sin OT internados entre 2016 y 2019. El grado de atrofia cerebral y de lesión de sustancia blanca se definieron según las escalas Global Cortical Atrophy y Age Related White Matter Changes (ARWMC), respectivamente. Se compararon los puntajes entre grupos. Se registró la mortalidad. Resultados: Se identificaron 16 pacientes con OT y 30 sin OT pareados según edad y sexo. La edad promedio del grupo con OT fue 80 años. El 87.5% fueron mujeres. La encefalopatía multifactorial fue el diagnóstico más frecuente seguido de la encefalopatía metabólica. El grado de atrofia fue mayor en pacientes con OT (10.43 vs 6.9, p= 0.03). El puntaje ARWMC fue 9.43 ±6.5 y 8.5 ±7.89 en pacientes con y sin OT respectivamente (p= 0.5). La mortalidad fue mayor en el grupo con OT (31.25 vs 6.66% p= 0.02). Conclusiones: Pacientes con encefalopatía aguda y OT tuvieron mayor grado de atrofia cerebral. Dicha alteración estructural podría relacionarse con la aparición de OT. No hubo diferencias significativas en el grado de lesión de sustancia blanca. La mortalidad del grupo con OT fue elevada. Son necesarios estudios para determinar su valor pronóstico.

Case Report: Triphasic Waves in a 9-Year-Old Girl With Anti-NMDAR Encephalitis.

BACKGROUND: Triphasic waves (TWs) are mainly described in association with metabolic encephalopathy, especially hepatic encephalopathy. Now, as different conditions including non-metabolic and structural abnormalities have been reported to be associated with TWs, the presence of TWs becomes a non-specific finding for metabolic encephalopathy. CASE PRESENTATION: We report the first case of anti-NMDAR encephalitis in a 9-year-old girl presenting with TWs on EEG. The TWs background EEG lasted for about 12 h on the 40th day of the disease course. No epileptic wave was found during a series of EEG examinations. The child was discharged from the hospital and no neurological sequelae remained after a six-month follow-up. CONCLUSIONS: TWs are not specific to metabolic encephalopathy, but can also occur in children with autoimmune encephalitis. This case achieved a good prognosis after the early initiation of immunotherapy.

Case Report: PRES-Like Syndrome With Reversible Cortical Blindness Associated With Essential Thrombocythemia.

Background: There are few reported cases of posterior reversible encephalopathy syndrome (PRES) combined with essential thrombocythemia (ET). We report a case of PRES-like syndrome in ET. Case Report: A 60-year-old man with a history of hypertension and thrombocythemia presented with progressive visual loss after waking up; and neurological examination showed pupils were 3 mm and equally reactive to light, which suggested cortical blindness. Brain magnetic resonance imaging (MRI) revealed restricted diffusion in diffusion-weighted imaging (DWI) in the bilateral parietal and occipital lobes. Routine blood tests revealed a platelet count of 1,044 × 109/L. ET was diagnosed after exclusion of other causes. Electroencephalography (EEG) showed periodic triphasic waves in the occipital region. The lesions of the parietal and occipital lobes on MRI and periodic triphasic waves of EEG disappeared quickly, and patient's vision returned to normal after the treatment with hydroxyurea and sodium bicarbonate. The patient experienced hallucinatory palinopsia during the recovery of vision. Conclusion: ET may be a risk factor for PRES.

Stimulus-Induced Rhythmic or Periodic Intermittent Discharges (SIRPIDs) in patients with triphasic waves and Creutzfeldt-Jakob disease.

Since the term Stimulus-Induced Rhythmic, Periodic, or Ictal Discharges (SIRPIDs) was introduced into the vocabulary of electrophysiologists/neurologists, there has been an ongoing debate about its significance, as well as its correlation with outcomes. SIRPIDs are frequently seen in patients who are critically ill from various causes. The literature reflects the findings of triphasic morphology, with the generalized periodic discharge (GPD) classification in many patients with SIRPIDs: toxic/metabolic encephalopathies, septic, and hypoxemic/hypercapnic encephalopathies, but also sharp periodic complexes in Creutzfeldt-Jakob disease and advanced Alzheimer's disease. In these settings, GPDs disappear when patients fall asleep and reappear when patients spontaneously wake up, or are awoken by an external stimulus, or sometimes because of a respiratory event, with the possibility of the appearance of GPDs with a cyclic alternating pattern. SIRPIDs may be seen as a transitional pattern between sleep and waking states, corresponding to a postarousal/awakening phenomenon. As SIRPIDs are a transient phenomenon and can usually be recorded repeatedly with each stimulation, the word "Ictal" could be replaced by "Intermittent": Stimulus-Induced Rhythmic or Periodic Intermittent Discharges. However, considering that SIRPIDs may be "potentially ictal" or on an "ictal-interictal continuum" in some situations, the "plus" modifier may be added: SIRPIDs-plus.

Generalized Periodic Discharges With Triphasic Morphology in the Setting of Aztreonam Neurotoxicity.

Generalized periodic discharges with triphasic morphology (GPDs + TWm) have been reported with multiple metabolic and drug toxicities. Beta-lactam antibiotics in some cases can cause neurotoxicity with GPDs + TWm on EEG. There are no reports in the literature of aztreonam causing neurotoxicity and GPDs + TWm. Here we describe GPDs + TWm and encephalopathy developing in a patient with underlying dementia and acute kidney injury who was started on aztreonam for cystitis. Neurotoxic effects of beta-lactam antibiotics have been well studied at this point, likely related to GABA receptor antagonism by the beta lactam ring. Risk factors for toxicity include, advanced age, prior neurological injury and decreased renal clearance. This patient carried multiple risk factors for beta-lactam neurotoxicity. Discontinuation of aztreonam led to a resolution of GPDs + TWm on EEG, and regression of encephalopathy.

A Treatable Encephalopathy in a Peritoneal Dialysis Patient - Cefepime-Induced Encephalopathy.

We report a patient with end-stage renal disease on peritoneal dialysis, who developed encephalopathy after receiving a few doses of cefepime. He recovered clinically and electroencephalographically after having discontinued the culprit agent and undergone hemodialysis. This case highlights the importance of promptly recognizing this reversible encephalopathy, which can lead to the avoidance of unnecessary workup, reduce the length of hospital stay, and thereby improve the patients' outcome.

Encephalopathy Induced by High Plasma and Cerebrospinal Fluid Ceftriaxone Concentrations in a Hemodialysis Patient.

Encephalopathy is a rare side effect of cephalosporin treatment. We herein present a case of encephalopathy induced by ceftriaxone, a third-generation cephalosporin, in a patient with renal failure. An 86-year-old woman on maintenance hemodialysis received ceftriaxone for Helicobacter cinaedi bacteremia. Her mental status deteriorated during antibiotic treatment, and an electroencephalogram revealed triphasic waves predominantly in the frontal area. Her consciousness improved after the discontinuation of the antibiotic due to the suspicion of ceftriaxone-induced encephalopathy. This is the first reported case of encephalopathy associated with high plasma and cerebrospinal fluid ceftriaxone concentrations, and provides significant evidence for a causal relationship between the administration of ceftriaxone and the onset of encephalopathy.

Generalized periodic discharges with triphasic morphology

Generalized periodic discharges (GPDs) with triphasic morphology are an electroencephalographic (EEG) pattern traditionally associated with encephalopathy and coma, although they have been observed in a wide array of neurological disorders. The clinical significance of these waveforms and their relationship to seizures and prognosis has been debated, and differentiation between interictal patterns, patterns associated with seizures, and patterns representing nonconvulsive status epilepticus can at times be a challenge. The most established literature suggests that GPDs, including those with triphasic morphology, are associated with the development of electrographic seizures, but that in the absence of clinical information, distinguishing waveforms based on morphology alone may not be clinically useful. Recent work has advocated for a more proactive approach in evaluating GPDs with triphasic morphology. Further studies of nonsedating antiseizure drugs in patients with GPDs with triphasic morphology that incorporate continuous EEG monitoring will be useful in tailoring therapy to optimize long-term clinical outcomes and recovery.

Generalized periodic discharges and 'triphasic waves': A blinded evaluation of inter-rater agreement and clinical significance.

OBJECTIVES: Generalized periodic discharges (GPDs) are associated with nonconvulsive seizures. Triphasic waves (TWs), a subtype of GPDs, have been described in relation to metabolic encephalopathy and not felt to be associated with seizures. We sought to establish the consistency of use of this descriptive term and its association with seizures. METHODS: 11 experts in continuous EEG monitoring scored 20 cEEG samples containing GPDs using Standardized Critical Care EEG Terminology. In the absence of patient information, the inter-rater agreement (IRA) for EEG descriptors including TWs was assessed along with raters' clinical EEG interpretation and compared with actual patient information. RESULTS: The IRA for 'generalized' and 'periodic' was near-perfect (kappa=0.81), but fair for 'triphasic' (kappa=0.33). Patients with TWs were as likely to develop seizures as those without (25% vs 26%, N.S.) and surprisingly, patients with TWs were less likely to have toxic-metabolic encephalopathy than those without TWs (55% vs 79%, p<0.01). CONCLUSIONS: While IRA for the terms "generalized" and "periodic" is high, it is only fair for TWs. EEG interpreted as TWs presents similar risk for seizures as GPDs without triphasic appearance. GPDs are commonly associated with metabolic encephalopathy, but 'triphasic' appearance is not predictive. SIGNIFICANCE: Conventional association of 'triphasic waves' with specific clinical conditions may lead to inaccurate EEG interpretation.

Syndrome of transient headache and neurological deficits with cerebrospinal fluid lymphocytosis (HaNDL): A case report with serial electroencephalography (EEG) recordings.. Is there an association with human herpes virus type 7 (HHV-7) infection?

Introduction The syndrome of transient headache and neurological deficits with cerebrospinal fluid lymphocytosis (HaNDL) is a diagnosis made by exclusion. In the literature, different etiological explanations are proposed for HaNDL, including an immune-mediated reaction after a viral infection. Case description We present a case of a 23-year-old woman with several episodes of transient headache, neurological deficits and cerebrospinal fluid lymphocytosis. All diagnostic criteria for the HaNDL syndrome were fulfilled; however, additional cerebrospinal fluid analysis showed a positive polymerase chain reaction (PCR) for human herpes virus type 7 (HHV-7). Discussion The possible role of a (prodromal) viral infection in the etiology of HaNDL is discussed. Also the role of electroencephalography (EEG) recordings is discussed. Serial EEG recordings showed generalized slowing, frontal intermittent rhythmic delta activity (FIRDA) and symmetric triphasic frontal waves with a dilation lag.

Response Rates to Anticonvulsant Trials in Patients with Triphasic-Wave EEG Patterns of Uncertain Significance.

BACKGROUND: Generalized triphasic waves (TPWs) occur in both metabolic encephalopathies and non-convulsive status epilepticus (NCSE). Empiric trials of benzodiazepines (BZDs) or non-sedating AED (NSAEDs) are commonly used to differentiate the two, but the utility of such trials is debated. The goal of this study was to assess response rates of such trials and investigate whether metabolic profile differences affect the likelihood of a response. METHODS: Three institutions within the Critical Care EEG Monitoring Research Consortium retrospectively identified patients with unexplained encephalopathy and TPWs who had undergone a trial of BZD and/or NSAEDs to differentiate between ictal and non-ictal patterns. We assessed responder rates and compared metabolic profiles of responders and non-responders. Response was defined as resolution of the EEG pattern and either unequivocal improvement in encephalopathy or appearance of previously absent normal EEG patterns, and further categorized as immediate (within <2 h of trial initiation) or delayed (>2 h from trial initiation). RESULTS: We identified 64 patients with TPWs who had an empiric trial of BZD and/or NSAED. Most patients (71.9%) were admitted with metabolic derangements and/or infection. Positive clinical responses occurred in 10/53 (18.9%) treated with BZDs. Responses to NSAEDs occurred in 19/45 (42.2%), being immediate in 6.7%, delayed but definite in 20.0%, and delayed but equivocal in 15.6%. Overall, 22/64 (34.4%) showed a definite response to either BZDs or NSAEDs, and 7/64 (10.9%) showed a possible response. Metabolic differences of responders versus non-responders were statistically insignificant, except that the 48-h low value of albumin in the BZD responder group was lower than in the non-responder group. CONCLUSIONS: Similar metabolic profiles in patients with encephalopathy and TPWs between responders and non-responders to anticonvulsants suggest that predicting responders a priori is difficult. The high responder rate suggests that empiric trials of anticonvulsants indeed provide useful clinical information. The more than twofold higher response rate to NSAEDs suggests that this strategy may be preferable to BZDs. Further prospective investigation is warranted.

Uncovering clinical and radiological associations of triphasic waves in acute encephalopathy: a case-control study.

BACKGROUND AND PURPOSE: Triphasic waves (TWs) are archetypal waveforms seen on electroencephalography (EEG) in some forms of encephalopathy. Their particular underlying pathological substrates are largely unexplored. This case-control study was designed to identify and quantify specific clinical and neuroradiological associations underlying TWs and to determine if TWs predicate outcome. METHODS: From 2004 to 2012, adult encephalopathic patients with TWs (cases) were matched 1:1 with encephalopathic patients without TWs (controls) by Glasgow Coma Scale (GCS) and the frequency range of EEG background activity. Clinical characteristics, neuroimaging and outcomes were assessed. RESULTS: The mean age of 190 patients (95 with and 95 without TWs) was 66.6 years (±15.6). In multivariable analyses, patients with TWs had significantly higher odds for liver insufficiency [odds ratio (OR) = 8.10, 95% confidence interval (CI) 1.98-33.08], alcohol abuse (OR = 3.65, 95% CI 1.25-10.63), subcortical brain atrophy (OR = 2.82, 95% CI 1.39-5.71) and respiratory tract infections (OR = 1.28, 95% CI 1.01-4.71). With each additional independent predictor, the odds increased for the occurrence of TWs (1 predictor, OR = 2.40, 95% CI 1.16-5.13; ≥2 predictors, OR = 9.20, 95% CI 3.27-25.62). Mortality was 15% and tended to be higher in patients with TWs (19% with vs. 11% without TWs). CONCLUSIONS: Alcohol abuse, liver insufficiency, infections and subcortical brain atrophy were independently associated with TWs in patients matched for clinical and EEG features of encephalopathy. These associations strengthen the hypothesis that TWs evolve from an interplay of pathological neurostructural, metabolic and toxic conditions. When matched for EEG background activity and GCS, TWs were not associated with death.

Significance of Triphasic Waves in Metabolic Encephalopathy / 대한임상신경생리학회지

BACKGROUND: Triphasic waves are one of the electroencephalographic patterns that can be usually seen in metabolic encephalopathy. The aim of this study is to compare the clinical and electrophysiologic profiles between patients with and without triphasic waves in metabolic encephalopathy, and reassess the significance of triphasic waves in metabolic encephalopathy. METHODS: We recruited 127 patients with metabolic encephalopathy, who were admitted to our hospital. We divided these admitted patients into two groups; those with and without triphasic waves. We analyzed the difference of duration of hospitalization, mortality rate during admission, Glasgow Coma Scale, severity of electroencephalographic alteration, and presence of acute symptomatic seizures between these two groups. RESULTS: Of the 127 patients with metabolic encephalopathy, we excluded 67 patients who did not have EEG, and 60 patients finally met the inclusion criteria for this study. Patients with triphasic waves had more severe electroencephalographic alterations, lower Glasgow Coma Scale, and more acute symptomatic seizures than those without triphasic waves. After adjusting the clinical variables, Glasgow Coma Scale and acute symptomatic seizures were only significantly different between patients with and without triphasic waves. CONCLUSIONS: We demonstrated that patients with triphasic waves in metabolic encephalopathy had more significant impairment of the brain function.

Significance of triphasic waves in patients with acute encephalopathy: a nine-year cohort study.

OBJECTIVE: Triphasic waves (TWs) are a frequent electroencephalography (EEG) finding in encephalopathy, yet their origin and prognostic significance are not well understood. The aim of this study was to determine the clinical and EEG characteristics in encephalopathic patients with TWs. We hypothesized that specific EEG characteristics are predictive of outcome. METHODS: Consecutive adult encephalopathic patients with TWs on EEG and neuroimaging were included. EEG analysis included semiquantitative evaluation of TWs, background activity, and EEG reactivity. The study endpoint was death. RESULTS: Over a nine-year period, 105 patients with TWs were included. Common abnormalities on neuroimaging were white matter lesions (60%) and cerebral atrophy (59%). Pathologic conditions included infections (56%), renal (50%) and liver insufficiency (12%), and respiratory failure (20%). Mortality was 20%. Absent EEG background reactivity and respiratory failure were independently associated with death (OR 3.73, 95%CI 1.08-12.80, p=0.037 and OR 6.47, 95%CI 1.98-21.12, p=0.02). CONCLUSIONS: These results suggest that TWs are a marker of structural brain disease coupled with toxic-metabolic perturbations, and that etiologies or underlying pathologies were not predictive for outcome while non-reactive EEG was independently associated with death. SIGNIFICANCE: In contrast to clinical, EEG and neuroimaging findings, non-reactive EEG patterns predicted death in encephalopathic patients with TWs.