Kaplan, Peter W.

Abstract 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.

Purpose: Electroencephalogram is used for prognostication and diagnosis in critically ill patients and is vital in developing clinical management algorithms. Unique waveforms on EEG may distinguish neurological disorders and define a potential for seizures. To better characterize zeta waves, we sought to define their electroclinical spectrum. Methods: We performed a systematic review using MEDLINE, Embase, Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Review [through Ovid], Scopus, Science Citation Index Expanded and Emerging Sources Citation Index [through the Web of Science], and Epistemonikos. Grey literature resources were searched. Results: Five hundred thirty-seven articles were identified. After excluding duplicates and reviewing titles, abstracts, and bodies and bibliographies of articles, four studies reported 64 cases describing data from patients with zeta waves, with a prevalence of 3 to 4%. Various and often incomplete clinical, neuroimaging, and EEG data were available. 57 patients (89.1%) had a focal cerebral lesion concordant with the location of zeta waves on EEG. 26 patients (40.6%) had clinical seizures, all but one being focal onset. Thirteen patients (20%) had epileptiform activity on EEG. Typically, zeta waves were located in the frontal head regions, often with generalized, frontal, predominant, rhythmic delta activity and associated with focal EEG suppression. Conclusions: Zeta waves frequently represent an underlying focal structural lesion. Their presence suggests a heightened risk for seizures. The small number of retrospective cases series in the literature reporting zeta waves might be an underrepresentation. We suggest a need for prospective studies of cEEG in critically ill patients to determine their clinical significance.

Summary: Prognostication following cardiorespiratory arrest relies on the neurological examination, which is supported by neuroimaging and neurophysiological testing. Acute posthypoxic myoclonus (PHM) is a clinical entity that has prognostic significance and historically has been considered an indicator of poor outcome, but this is not invariably the case. “Malignant” and more “benign” forms of acute PHM have been described and differentiating them is key in understanding their meaning in prognosis. Neurophysiological tests, electroencephalogram in particular, and clinical phenotyping are crucial in defining subtypes of acute PHM. This review describes the neurophysiological and phenotypic markers of malignant and benign forms of acute PHM, a clinical approach to evaluating acute PHM following cardiorespiratory arrest in determining prognosis, and gaps in our understanding of acute PHM that require further study.

Purpose: Periodic discharges (PDs) are EEG patterns denoting brain dysfunction and ictal tendency. Their exact meaning regarding etiology and outcomes is not well known. In particular, bilateral independent PDs (BIPDs) are poorly described. Methods: We performed a retrospective, multicenter study evaluating neuroimaging, epileptic, clinical, and EEG correlates of BIPDs. Results: Twenty-five patients studied with a mean Glasgow Coma Scale 6.5 and modified Rankin scale 3.9 who underwent EEG monitoring, mean duration 287 hours (range 0.75–3,216). Most common causes of BIPDs were cardiac arrest, Central Nervous System infections, and acute/chronic ischemic/hemorrhagic stroke. Most had subcortical and cortical injuries on neuroimaging. Most of the PDs ranged from 0.5 to 2 Hz in frequency, were of multiple phase types, and localized to the frontal head regions. Eighteen of 25 patients had clinical or electrographic seizures. There was a trend toward seizures in those with BIPDs with a history of epilepsy (P = 0.08) and acute metabolic dysfunction (P = 0.08), particularly with coincident acute structural lesions (P = 0.05). Seizures were predicted by bilaterally symmetric frequencies (P = 0.02) and trended toward higher likelihood with PD frequency <2 Hz (P = 0.08). Two of 25 patients survived past discharge with modified Rankin scale <3. Cardiac arrest was associated with withdrawal of life-sustaining therapy (P < 0.001). Conclusions: BIPDs arise from acute and chronic neurologic injuries, often associated with metabolic dysfunction. Outcomes are poor in this population. Seizures are common, particularly in patients with PDs that are of a lower frequency or are symmetric in frequency. Further study is warranted to evaluate the association between BIPDs and seizures, as well as functional and longer term outcomes.