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

Discharges With Triphasic Morphology as Marker of the Risk of Death in Acute Encephalopathy

Introduction. In clinical practice, it is difficult to define the prognosis of patients with acute encephalopathy; a syndrome characterized by cognitive dysfunction and altered sensorium. Discharges with triphasic morphology (DTM) are an electroencephalographic pattern that might be useful to establish the risk of death. The aim of this study was to define the prognostic value of DTM regarding mortality in patients with acute encephalopathy. Methods. We conducted an observational retrospective cohort study including patients with acute encephalopathy with and without DTM paired by age and gender in a 1:2 ratio. We calculated the odds ratio (OR) to determine the association between DTM and mortality. In addition, we calculated sensibility, specificity, and predictive values. Results. We included 72 patients, 24 with DTM and 48 without DTM. Mortality was higher in patients with DTM (41.6% vs 14.5%, P  =  .01). Factors associated with a higher risk of death were DTM (OR  =  4.1, 95% confidence interval [CI] 1.3-13, P  =  .01) and sequential organ failure assessment score (OR  =  1.3, 95% CI 1.04-1.67, P  =  .02). A higher Glasgow coma scale score was associated with a lower risk of death (OR  =  0.65, 95% CI 0.51-0.83, P  =  .001). The sensibility and specificity of DTM were 59% and 75%, respectively. Positive and negative likelihood ratios were 2.36 and 0.55. Discussion. Our results revealed high mortality in patients with acute encephalopathy and DTM. This electroencephalographic pattern was associated with 4 times higher risk of death. However, its usefulness for predicting death was limited.

Atypical or Typical Triphasic Waves-Is There a Difference? A Review

SUMMARY

The entity of triphasic waves (TWs) and TW encephalopathy has derived from the subjective art of EEG interpretation. Indeed, there are few if any guidelines regarding many different aspects of TWs. The authors seek to shed light on the nature and the diagnostic characteristics of various types of TWs, differentiating "typical" from "atypical" forms. The authors conclude that morphologies in the form of bursts of well-formed, smoothly contoured, negative-positive-negative, bilateral, symmetrical and synchronous, regular, reactive, periodic or rhythmic, 1.5 to 2.0 Hz, fronto-central, triphasic complexes with fronto-occipital lag meet the criteria for typical TWs and are highly suggestive of toxic-metabolic encephalopathies. These are most frequently hepatic, uremic, or sepsis-associated encephalopathies with multi-organ failure. In such cases, atypical TWs (frontopolar or parieto-occipital maximum, negative-positive or negative-positive-negative, asymmetric and asynchronous, unreactive, irregular, multifocal, continuous with spatiotemporal evolution, sharper and without fronto-occipital/occipito-frontal lag, or triphasic delta waves) are rarely seen. Atypical TWs are encountered in Angelman syndrome, toxic encephalopathies, hyperthyroidism/hypothyroidism, Hashimoto encephalopathy, nonconvulsive status epilepticus, dementia, sepsis-associated encephalopathy, cerebrovascular disorders, and certain boundary syndromes. Investigations describing TWs with uncommon etiologies revealed few with typical TWs, suggesting that the term "TWs" has been overused in the past. Triphasic waves arise from the interaction of multiple factors including toxic, metabolic, infectious, and structural disorders that affect circuits between thalamus and cortex. The patient's metabolic status, presence of potentially neurotoxic drugs, cerebral atrophy, white matter disease, dementia, or seizures help differentiate typical from typical TWs. Future studies will determine whether this dichotomy is heuristically and clinically helpful.

White Matter Disease-The True Source of Triphasic Waves?

SUMMARY

Triphasic waves are EEG phenomena typically seen in patients with acute encephalopathy and have importance in diagnosis and prognosis in these cases. The underlying metabolic disturbances associated with their incidence have been described previously, but neuroimaging characteristics are not well delineated. There are a few small studies that define neuroimaging results in patients with triphasic waves. This review highlights the most common neuroimaging findings in these patients, including subcortical white matter disease, which itself may be a risk factor for triphasic waves.

An EEG Voyage in Search of Triphasic Waves-The Sirens and Corsairs on the Encephalopathy/EEG Horizon: A Survey of Triphasic Waves

SUMMARY

Generalized periodic discharges with triphasic wave (TW) morphology, long referred to as TWs, are typical of many toxic, metabolic, infectious, and cerebral structural problems, often in concert. Identifying TWs has been challenging for the electroencephalographer and clinician, as has been their cause, significance, prognosis, and treatment. This review highlights the many different patterns of TWs with commentary on their various causes and etiologies, characteristics, different morbidities, differentiation from nonconvulsive status epilepticus, and their prognosis. The articles in this Journal of Clinical Neurophysiology special issue on TWs will review the many challenges the clinician face when TWs are sighted.

Triphasic Waves: Historical Overview of an Unresolved Mystery

SUMMARY

Triphasic waves are a fascinating and mysterious EEG feature. We now have to accept that, at times, epileptiform discharges may have a blunted "triphasic morphology," and that there may be great difficulty in distinguishing between these often similar forms. The aim of this review was to describe the evolution in our understanding of triphasic waves that has occurred regarding the pathophysiology of triphasic waves, their most frequent causes, and the diagnostic difficulties involved in interpretation and differentiation from nonconvulsive status epilepticus.

Neuroimaging in Triphasic Waves

SUMMARY

Triphasic waves can be seen in a wide range of medical conditions, particularly in metabolic encephalopathies. Neuroimaging studies provide valuable diagnostic information for neurological conditions and can also help in our understanding of anatomical substrates for these conditions. Because of practical challenges and the fact that most encephalopathies with triphasic waves are presumed to be metabolic in etiology, large studies of imaging findings associated with triphasic waves are limited. We present a summary of studies that are currently available and a discussion of insights that these studies provide.

Triphasic Waves Are Generated by Widespread Bilateral Cortical Networks

PURPOSE

Triphasic waves (TWs) have been observed in the EEG recorded in patients with various types of encephalopathy, yet their genesis and significance is still debated. The aim of this study was to elucidate the localization of the cortical generators of TWs using EEG source imaging.

METHODS

In 20 consecutive patients who had encephalopathy with TWs, EEG source imaging of the first negative and the positive phases of the TW was performed. Three different approaches were used: equivalent current dipoles, a distributed source model, and a recently described spatial filtration method for visualizing EEG in source space.

RESULTS

Equivalent current dipole models failed to provide valid solutions. The distributed source model and the spatial filtration method suggested that TWs were generated by large, bilateral cortical networks, invariably involving the anterior frontal and the temporo-polar areas.

CONCLUSIONS

Source imaging localized TWs to anterior frontal and temporo-frontal structures. Involvement of these regions is consistent with the typical pathophysiological changes of altered consciousness and cognitive changes observed in patients with TW encephalopathy.

Are Triphasic Waves Different From Generalized Spike-Wave Discharges?

SUMMARY

Generalized periodic discharges with triphasic morphology were previously referred to as triphasic waves but have now been subsumed into the ACNS classification as generalized periodic discharges. Although triphasic waves and generalized spike-wave complexes may resemble each other and hence may be incorrectly identified in comatose critically ill patients, many authors believe that there are different entities, with definable morphologic and clinical differences attributable to each waveform. The occurrence of both patterns in the same patient is extremely rare with only a single prior case report. Here the authors report a patient with typical triphasic waves and generalized spike-wave complexes and highlight the morphologic and EEG differences between the two patterns. The occurrence of both waveforms in the same EEG recording supports the notion of different cerebral generators and pathways, further differentiating rather than merging these morphologies.

Clinical and Radiological Correlates of Different Electroencephalographic Pattern in Hospitalized Patients

Objective. The present study aimed to determine the clinical and radiological correlates of different electroencephalographic (EEG) patterns in hospitalized patients. Subjects and Methods. In this retrospective study performed at the Neurology Department, King Fahd University Hospital, Kingdom of Saudi Arabia (KSA), data of 374 patients who underwent EEG were reviewed and analyzed. Results. Presence of focal spike and wave or sharp wave (SW) (P = .00), generalized theta activity (P = .00), generalized delta activity (P = .04), persistent focal slow wave activity (SWA) (P = .003) and asymmetric background (P = .01) in the EEG record was significantly associated with abnormal imaging findings. Specifically, generalized theta delta activity (P = .01) and markedly attenuated EEG activity (P = .007) were associated with presence of cortical lesions; whereas, triphasic waves (TWs) (P = .009), and generalized theta activity (P = .001) were found to be related with presence of subcortical lesions. While, generalized delta activity (P = .01) was the only correlate with extra-axial lesions. Conclusion. At present, certain EEG patterns cannot be precisely correlated with imaging findings, suggesting that intercurrent metabolic, infectious, and/or toxic contributors could be the confounding factors. Nonetheless, when EEG patterns are examined alongside magnetic resonance imaging findings and other clinically relevant data, these might be indicative of a group of diseases in some pertinent situations. Thus, further larger prospective clinical studies that incorporate continuous EEG monitoring, advanced radiology techniques, and laboratory analyses would be beneficial to elucidate their interplay for better firm up the correlations.

Source Analysis of Triphasic Waves Using Quantitative Neuroimaging

PURPOSE

Triphasic waves (TWs), a common EEG pattern, are considered a subtype of generalized periodic discharges. Most patients with TWs present with an altered level of consciousness, and the TW pattern is believed to represent thalamocortical dysfunction. However, the exact meaning and mechanism of TWs remain unclear. The objective of the current study was to evaluate the source of TWs using EEG source imaging and computerized tomography.

METHODS

Twenty-eight patients with TWs were investigated. Source analysis was performed on the averaged TWs for each individual, and source maps were extracted. Normalization and automatic segmentation of gray matter were performed on computerized tomography scans before analysis. Finally, voxelwise correlation analyses were conducted between EEG source maps and gray matter volumes.

RESULTS

Source analyses showed that the anterior cingulate cortex was mainly involved in TWs (16/28 patients, 57%). Correlation analyses showed moderate positive and negative correlations between source location and gray matter volumes for the posterior cingulate (T = 2.85; volume = 6,533 mm3; r = 0.53; P = 0.002) and the superior frontal gyrus (T = 2.54; volume = 18,167 mm3; r = -0.48; P < 0.0001), respectively.

CONCLUSIONS

The results suggest that the anterior cingulate is involved in the origin of TWs. Furthermore, the volumes of posterior brain regions were positively correlated with TWs, indicating a possible preservation of these structures. Conversely, the volumes of anterior regions were negatively correlated with TWs. These findings may indicate a structural pattern necessary for the generation of the abnormal network responsible for TWs.

Acute Toxicity and Triphasic Waves-The Example of Cefepime

PURPOSE

Triphasic waves (TWs) have been associated with a host of medication toxicities, and cefepime has emerged recently as a frequently encountered offending agent. This investigation aims to evaluate cefepime-induced encephalopathy and to report the associated clinical, EEG expression with TWs, and the radiologic findings.

METHODS

A retrospective multicenter observational study examining adult patients with cefepime-induced encephalopathy with generalized periodic discharges on either routine or continuous EEG between January 2014 and January 2020. Clinical, electrographic, and radiologic data were collected. Patients in whom cefepime was not the sole causative factor for their encephalopathy were excluded.

RESULTS

Twenty-seven patients with cefepime-induced encephalopathy marked by generalized periodic discharges with triphasic morphology were identified at both centers, whereas no patients were presenting with generalized periodic discharges without TWs. Patients had a median age of 63 years (interquartile range, 56-73). Fifty-six percent of the cohort (15 patients) were <65 years of age. Eighteen patients (67%) had either acute or chronic kidney impairment (either acute kidney injury or chronic kidney disease or both), whereas 81% had preexisting white matter disease on brain imaging. Of these, 14 patients (51%) were classified as either moderate or severe. In the majority of the patients, TWs were either state-dependent or stimulus-sensitive, and in one third of them presented only as stimulus-induced pattern. All patients improved with discontinuation of cefepime.

CONCLUSIONS

Cefepime toxicity should be considered in the differential diagnosis in encephalopathic patients with TWs. The presence of preexisting white matter disease in these patients should heighten the degree of suspicion, especially in younger patients and patients without renal dysfunction.

Electroencephalographic (EEG) features of encephalopathy in the setting of Covid-19: A case series

OBJECTIVE

The Covid-19 pandemic is a global challenge presenting clinicians with an evolving diagnostic landscape. We sought to describe EEG findings observed from local experience in a typical case series of patients with severe Covid-19.

METHODS

Ten cases of Covid-19 were identified in whom EEG recordings had been made during the course of admissions to Bristol hospitals which had required intensive care. Electro-clinical correlation between the EEG and available medical history, imaging and laboratory investigation results was explored.

RESULTS

The predominant EEG features in severe Covid-19 are of generalised symmetrical slowing, consistent with encephalopathy.

CONCLUSIONS

The presence of focal disturbances or irritative abnormalities may be a pointer away from a pure encephalopathy and warrant further investigation.

SIGNIFICANCE

A growing range of neurological sequelae from Covid-19 are now recognised to be common amongst patients hospitalised by with this condition, being seen to affect approximately one third of such cases. Electroencephalography has a unique place in the diagnostic work-up of impaired consciousness, a frequent feature of severe Covid-19. However, there is currently a paucity of literature describing typical EEG findings in this setting.

Clinical neurophysiology of altered states of consciousness: Encephalopathy and coma

The neurophysiologist will commonly encounter patients with encephalopathy/delirium (altered consciousness with impaired cognition, usually with sleep-wake cycle alteration and lethargy) or coma (an eyes-closed state of unresponsiveness) in the hospital setting. Assessing the background frequency of the EEG, as well as the presence or absence of other features (reactivity, periodic discharges such as triphasic waves), can provide insight into the patient's underlying condition and in some cases may provide prognostic information. The literature of postanoxic arrest EEG patterns continues to expand. Other neurophysiologic tests, such as somatosensory evoked potentials, auditory mismatch negativity, and even EMG, may also play a role in assessing brain function; distinguishing among a locked-in state, minimally conscious state, persistent vegetative state, and waking/unresponsive states; and assessing the potential for recovery after brain injury.

An update on the recognition and treatment of non-convulsive status epilepticus in the intensive care unit

INTRODUCTION

Non-convulsive status epilepticus (NCSE) is a complex and diverse condition which is often an under-recognised entity in the intensive care unit. When NCSE is identified the optimal treatment strategy is not always clear. Areas covered: This review is based on a literature review of the key literature in the field over the last 5-10 years. The articles were selected based on their importance to the field by the authors. Expert commentary: This review discusses the complex situations when a neurological consultation may occur in a critical care setting and provides an update on the latest evidence regarding the recognition of NCSE and the decision making around determining the aggressiveness of treatment. It also considers the ictal-interictal continuum of conditions which may be met with, particularly in the era of continuous EEG, and provides an approach for dealing with these. Suggestions for how the field will develop are discussed.

Cerebral Blood Flow Autoregulation in Sepsis for the Intensivist: Why Its Monitoring May Be the Future of Individualized Care

Cerebral blood flow (CBF) autoregulation maintains consistent blood flow across a range of blood pressures (BPs). Sepsis is a common cause of systemic hypotension and cerebral dysfunction. Guidelines for BP management in sepsis are based on historical concepts of CBF autoregulation that have now evolved with the availability of more precise technology for its measurement. In this article, we provide a narrative review of methods of monitoring CBF autoregulation, the cerebral effects of sepsis, and the current knowledge of CBF autoregulation in sepsis. Current guidelines for BP management in sepsis are based on a goal of maintaining mean arterial pressure (MAP) above the lower limit of CBF autoregulation. Bedside tools are now available to monitor CBF autoregulation continuously. These data reveal that individual BP goals determined from CBF autoregulation monitoring are more variable than previously expected. In patients undergoing cardiac surgery with cardiopulmonary bypass, for example, the lower limit of autoregulation varied between a MAP of 40 to 90 mm Hg. Studies of CBF autoregulation in sepsis suggest patients frequently manifest impaired CBF autoregulation, possibly a result of BP below the lower limit of autoregulation, particularly in early sepsis or with sepsis-associated encephalopathy. This suggests that the present consensus guidelines for BP management in sepsis may expose some patients to both cerebral hypoperfusion and cerebral hyperperfusion, potentially resulting in damage to brain parenchyma. The future use of novel techniques to study and clinically monitor CBF autoregulation could provide insight into the cerebral pathophysiology of sepsis and offer more precise treatments that may improve functional and cognitive outcomes for survivors of sepsis.

EEG for Diagnosis and Prognosis of Acute Nonhypoxic Encephalopathy: History and Current Evidence

The term encephalopathy encompasses a wide variety of complex syndromes caused by a large number of different toxic, metabolic, infectious, and degenerative derangements. Acute encephalopathy typically presents with a fluctuating course involving alteration of mental status or confusion and decreased (or rarely increased) motor activity. There usually are lethargy, cognitive impairment, altered memory and mental processing of information, and disturbed sleep-wake cycles. Encephalopathy mainly occurs in the elderly and is frequently encountered in intensive care units and postoperatively. Despite new diagnostic procedures and advances in intensive medical care, acute encephalopathy constitutes a significant cause of morbidity and mortality in hospitalized patients. EEG enables rapid bedside electrophysiological monitoring providing dynamic real-time information on neocortical brain activity and dysfunction. Hence, EEG complements clinical and neuroimaging assessments of encephalopathic patients. Progressive slowing of EEG background activity with increasing cerebral compromise, the emergence of episodic electrographic transients, seizures, and decreased EEG reactivity to external stimuli provide important diagnostic and prognostic information. The aim of this review was to provide a comprehensive overview of the current evidence for the diagnostic and prognostic value of EEG in adult intensive care unit patients with acute nonhypoxic encephalopathy.

Clinical, Electroencephalographic, and Neuroradiological Outcome Predictors in Acute Nonhypoxic Encephalopathy: A Nine-Year Cohort Study

Marked impairment of consciousness, brain lesion on neuroimaging, and nonreactive electroencephalographic (EEG) background activity are established outcome predictors in patients with hypoxic encephalopathy. In this observational cohort study, we aimed to assess the predictive value of clinical, neuroimaging and EEG characteristics for outcome in different types of acute nonhypoxic encephalopathic patients. All adult intensive care unit patients from a tertiary academic medical care center with clinical and EEG evidence of acute nonhypoxic encephalopathy were included from 2004 to 2012. Clinical data, neuroimaging studies, EEG characteristics, and outcome were assessed. In-hospital death was the main outcome. Median age of 262 patients was 65 years (range 18-98 years). Mortality was 12.6%. In Poisson regression analyses, older age (P=.02), intracranial hemorrhage (P=.008), coma (P=.012), and nonreactive EEG background activity (P<.0001) were independently associated with death with nonreactive EEG being the strongest predictor (relative risk 3.74; 95% confidence interval 2.02-6.91). Subgroup analysis revealed no significant effect modification for the predictive value of nonreactive EEG by the presence or absence of coma and different types of acute brain lesions. In conclusion, this study identifies and quantifies the independent predictive value of older age, intracranial hemorrhage, coma, and nonreactive EEG for death, in patients with different types of acute nonhypoxic encephalopathy. These results add further credence to the limited body of evidence that EEG provides important prognostic information in different types of acute encephalopathy not related to hypoxic brain injury. Further studies are warranted to analyze the robustness of this predictor in larger subpopulations with specific etiologies of acute nonhypoxic encephalopathies.

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.

Clinical neurophysiology of hepatic encephalopathy

BACKGROUND/OBJECTIVES

Hepatic encephalopathy (HE) has relevant impact on the quality of life of patients and their caregivers and causes relevant costs because of hospitalizations and work days lost. Its quantification is important to perform adequate clinical trials on this relevant complication of cirrhosis and portal-systemic shunting. Clinical neurophysiology, which detects functional alterations of the nervous system, has been applied to the study of HE for over 60 years. This review aims at summarizing and clarifying the role of neurophysiologic techniques in the study of HE.

METHODS

A narrative review was performed aiming at interpreting the cited papers and the techniques on the basis of their physiological and pathophysiological meaning.

RESULTS

The potential role of EEG, quantified EEG, evoked potentials-both exogenous, endogenous and motor-have been clarified to the reader that may be unfamiliar with neurophysiology.

CONCLUSIONS

The EEG, reflecting the oscillatory changes of neural network is the preferable tool to detect and monitor HE, with the exception of its most severe stage, when EEG flattens. SSEP and MEP have indication to detect and monitor transmission alterations that are likely related to myelin changes and microedema.