Prognostically important EEG coma patterns in diffuse anoxic and traumatic encephalopathies in adults

Because of the paucity in the English literature of a detailed and universally accepted EEG grading scale relating to survival after diffuse traumatic and anoxic brain insults, prognostically oriented EEG patterns including recently described abnormalities are presented and discussed. The significance of these patterns may also apply in cases of coma of other etiologies, which can present morphologically similar features. EEG patterns have been classified into five major grades based on an internationally accepted scale. Individual patterns have been more clearly defined on the basis of the morphology of dominant activities, their distribution, persistence, and reactivity to external stimulation. Favorable outcome with survival seems to occur with both grade 1 and the "reactive type" of grade 2 abnormalities, with preservation of normal sleep features, and with frontal monorhythmic delta activity. Prognostically uncertain patterns are "nonreactive" grade 2 abnormalities, diffuse delta activity with grade 3 abnormality, and the "reactive type of alpha pattern coma." The following patterns are suggested to be prognostically malignant if persistent: grade 3 abnormality with small amplitude, diffuse, irregular delta activity; grade 4 ("burst suppression pattern"), in particular when epileptiform discharges are present and with "low-output EEG"; and grade 5 ("isoelectric EEG"). Fatal outcome is also common with the "nonreactive type of alpha pattern coma" and the recently reported "theta pattern coma." These patterns are presented in the illustrations. It is intended that this more detailed subdivision will promote understanding between electroencephalographers using visual EEG assessment in cases of coma.     

Value of a revised EEG coma scale for prognosis after cerebral anoxia and diffuse head injury

The prognostic validity for survival of a recently devised EEG grading scale was tested in anoxic and post-traumatic coma. This scale divides EEG in coma into five major grades and ten subdivisions with emphasis on the presence of dominant activities, their amplitude, persistence, distribution and reactivity. In this scale, patterns previously not allocated, such as "spindle pattern coma," "alpha pattern coma," and "theta pattern coma" are also included. The prognostic power of the revised scale was tested retrospectively without knowledge of clinical data in a group of patients with cerebral anoxia after cardiac arrest lasting more than seven minutes and in a group of diffuse head injuries. The validity of the scale was found to be higher than those used in previously published studies, reaching 98.4% prognostic accuracy in anoxic encephalopathies and was very high in head injuries.     

Epileptiform discharges in presence of continuous background activity in anoxic coma

The EEGs of a group of patients in anoxic coma following cardiorespiratory arrest were retrospectively studied. Twelve of 70 patients had at least one EEG recorded during the acute period which consisted of epileptiform discharges in the presence of continuous diffuse background activity. Nine of the patients died while three made a generally favorable recovery. The analysis confirms the prediction of a recent revision of EEG grades in coma that this particular pattern of activity is of uncertain prognostic significance. This is in contrast to the occurrence of epileptiform discharges during discontinuous "burst suppression" activity which generally indicates a fatal outcome.     

"Theta pattern coma" occurring in younger adults

Since our previous report, where "theta pattern coma" was described in 2 elderly patients as an EEG pattern with a grave prognosis, we have had the opportunity to see another 9 affected patients. In this article, 3 men with a mean age of 36 years who died after cardiorespiratory arrest presented a "theta coma pattern." The EEG activity was initially reactive to and attenuated by external stimulation in 2, but prior to death the pattern became arreactive. This article shows that "theta pattern coma" is not an age related phenomenon as previously considered. So far, 11 patients with this type of EEG abnormality have been seen in our department; all have died, and all were over 30 years of age. An expanded definition of "theta pattern coma" is given in the discussion. The pathophysiological mechanisms involved in generation of this abnormality are not known. This abnormality, when seen in the unconscious patient, should be classified as a grade 4 abnormality on the EEG coma scale and should be differentiated from rather diffuse theta activity in coma. The prognostic significance of "theta pattern coma" appears to be similar to that of "alpha pattern coma."     

Clinical correlates and prognosis in early spindle coma.

OBJECTIVE: To determine the prognostic significance of spindle coma (SC) according to etiology and EEG reactivity.METHODS: We reviewed 15 patients with SC due to various causes within 8 days of coma to determine the prognostic significance of this EEG pattern.RESULTS: The outcome among survivors was favorable: among 13 survivors, 9 were independent in all activities of daily living (ADLs) at 6 months; 3 were dependent in all ADLs; and one remained in coma. EEG reactivity to noxious stimuli best predicted outcome: All patients (whatever the coma etiology) with EEG reactivity survived; conversely, not all patients without EEG reactivity died.CONCLUSION: In our patients, EEG reactivity independent of etiology predicted survival, neurological examination did not predict outcome. Most SC survivors had a meaningful recovery achieving all ADLs. From the literature, the cause of SC was predictive of outcome: encephalopathy, seizures and trauma had the best prognosis while hypoxia, CRA and structural lesions carried the worst. Literature review revealed that 23% of patients [56/242] died or remained in a persistent vegetative state (PVS). Best outcomes occurred when SC was due to drugs, encephalopathy or seizures: (0/14 died or were in a PVS). With trauma 15% [25/169] died or were in a PVS). Intermediate outcomes occurred with hypoxia and cardio-respiratory arrest (CRA): 33% [7/21] died or were in a PVS. The gravest outcomes occurred with brain-stem and cerebral infarctions, and tumors: 73% [22/30] died or were in a PVS.     

Prognostic value of dynamic electroencephalogram in comatose patients with different diseased regions

BACKGROUND: It has proved that dynamic electroencephalogram (EEG) is definite in judging the outcome of ischemic hypoxic comatose patients, EEG is more sensitive to the cortical affection, but not sensitive to the subcortical and brainstem affections, thus it is necessary to clarify the indications of this technique in the clinical application. OBJECTIVE: To observe and compare the prognostic value of dynamic EEG and Glasgow coma score in comatose patients with different diseased region. DESIGN: A clinical case-controlled observation. SETTING: Union Hospital of Fujian Medical University. PARTICIPANTS: Sixty-eight comatose patients were selected from the Union Hospital affiliated to Fujian Medical University from June 1998 to January 2005. The diseased regions were identified using cranial CT (n =43) or MR (n =25). According to different primarily diseased regions, the comatose patients were divided into two groups: ① brainstem affection group (n =23): 13 males and 10 females, 14–62 years of age; ② diffuse cortical affection group (n =45): 28 males and 17 females, 23–75 years of age. METHODS: The dynamic EEG and Glasgow coma score were examined in the 45 comatose patients with primarily cortical affection and 22 comatose patients with primarily brainstem affection at acute phase. The patients were followed-up for 3 months to observe the outcome, The termination of outcome judgment was 3 months after attack or the death. The clinical outcome was classified as complete rehabilitation, survived with disability, death or vegetative state. Correlations of dynamic EEG and Glasgow coma score with the outcome of patients were analyzed. The correlations of dynamic EEG grades and Glasgow coma scores with the outcome were analyzed, and the prognostic value of dynamic EEG grades was compared between the two groups. MAIN OUTCOME MEASURES: ① Correlations of dynamic EEG and Glasgow coma score with the outcome of patients; ② Comparison of the prognostic value of dynamic EEG grades between the two groups. RESULTS: All the 68 patients were involved in the analysis of results. ① Correlations of dynamic EEG grades and Glasgow scores and their correlation analysis: EEG grades had significant negative correlation with Glasgow coma scores in both the cortical affection group and brainstem affection group (r =–0.743, –0.564, P < 0.01, 0.05). In the cortical affection group, the Glasgow coma scores and dynamic EEG grades in the patients with the outcome of death or vegetative state were significantly different from those with the outcome of rehabilitation (P < 0.05–0.01). In the brainstem affection group, the Glasgow coma scores were only significantly different between the patients with outcome of rehabilitation and death (P < 0.05), and there was no significant difference in dynamic EEG grades among the three prognostic states (P > 0.05). ② Comparison of the prognostic value of dynamic EEG grades between comatose patients with cortical affection and brainstem affection: The sensitivity, specificity and accuracy were all higher (P < 0.05), while the error rate was lower (P < 0.05) in the cortical affection group than in the brainstem affection group. CONCLUSION: Dynamic EEG was valuable in predicting the outcome of comatose patients with primarily cortical affection, but it was not certainly valuable in those with primarily brainstem affection.     

Predictive value of P300 event-related potentials compared with EEG and somatosensory evoked potentials in non-traumatic coma

Developments in ethical decision making are increasing demand for more accurate predictions of outcome in coma. New neurophysiologic tests are needed to improve the ability to predict awakening as well as poor outcome. We have recently reported that the P300 event-related potential (P300) correlates with awakening and depth of nontraumatic coma. In this companion study, the predictive value of the P300 was compared with median nerve somatosensory evoked potentials (SEP) and EEG in 20 patients in non-traumatic coma. We also evaluated the predictive value of a simplified grading scale for both the EEG and SEP (the USC SEP scale and USC EEG scale). The resence of a P300 was significantly associated with higher Glasgow coma scores (GCS) and awakening. Severe abnormalities of the somatosensory evoked potentials significantly correlated with the absence of awakening and a low GCS. Moderate abnormalities of the SEP were significantly associated with awakening and higher GCS scores. the EEG was significantly associated with GCS score and severe abnormalities of the EEG were predictive of the absence of awakening and very low GCS scores. The data indicates that the P300 and SEP are more effective than the EEG in predicting awakening, and that the SEP and EEG are more effective than the P300 in predicting poor outcome. We conclude that, in addition to EEG and SEP, the P300 should be considered in the prognostic evaluation of patients in nontraumatic coma. Further, simplified scales for the EEG and SEP are predictive of depth of coma and outcome.     

Concomitant administration of sodium dichloroacetate and thiamine in west syndrome caused by thiamine-responsive pyruvate dehydrogenase complex deficiency

IRDA (intermittent rhythmic delta activity) is an abnormal generalized EEG pattern that is not specific to any single etiology and can occur with diffuse or focal cerebral disturbances. To determine whether different electrographic features of IRDA and associated EEG findings can differentiate underlying focal from diffuse brain disturbances, we performed a blind analysis of 58 consecutive EEGs with an IRDA pattern, recorded from 1993 until 1996, in which we evaluated posterior background activity, focal slowing and IRDA characteristics (frequency, distribution, duration, symmetry and abundance). The clinical diagnosis, state of consciousness and CT brain findings were retrieved from the patients' hospital records. There were 58 patients (33 females; mean age, 58+/-21 years). Twelve (21%) had only focal brain lesions, while 46 (79%) had diffuse brain abnormalities, (15 diffuse structural, 19 metabolic abnormalities, 12 postictal). Normal consciousness and focal EEG slowing were more frequent in patients with focal abnormalities, however, this was not statistically significant. Of the patients with focal abnormality, 11 (92%) had normal posterior background activity either bilaterally (n=4) or contralateral to the focal lesion (n=7). Bilaterally normal posterior background activity was observed in about 30% in both groups. Bilaterally abnormal posterior background activity was apparent in one patient (8%) with focal brain lesion and in 31 patients (67%) with diffuse brain abnormalities (P<0.0001). There were no significant differences in IRDA electrographic features between the focal group and the group with diffuse brain disturbances. We conclude that IRDA morphology cannot distinguish between focal and diffuse brain abnormalities.     

Electrophysiological prognostication and brain injury from cardiac arrest

Anoxic coma after cardiorespiratory arrest warrants precocious investigation to establish probable outcome. Electroencephalogram (EEG) may uncover subclinical seizures; EEG grades have provided accurate prognosis of poor and favorable outcomes, but are weakest in those patients in between. Somatosensory evoked potentials now have proven benefit in accurately establishing a poor outcome (death or persistent vegetative state) when cortical responses (N20) are absent. These studies are particularly helpful when clinical examination of coma, early on, might yield uncertain prognosis (i.e., when brain stem reflexes are present). Combining clinical examination with electrophysiology has increasingly yielded multimodality approaches to early prognostication of coma after cardiorespiratory arrest, with more recent studies using event-related and middle-latency potentials showing promise for distinguishing good outcome (to consciousness), from awake but vegetative states. Further studies are warranted for this multimodality approach which, hopefully, may yield more widespread practical use of these testing modalities.     

"Alpha-pattern coma" in high voltage electrical injury.

Two cases are reported in which reversible deep coma subsequent to high voltage electrical injury occurred in association with alpha frequencies in the EEG. The EEG pattern differs from the alpha rhythm of the normal awake patient by its diffuse distribution and unresponsiveness to a variety of stimulation. The term "alpha-pattern coma" is introduced to designate the occurrence of this pattern in comatose patients. The EEG in the cases described initially demonstrated activity in the alpha frequency which occurred in a generalized distribution and was unresponsive to stimulation. During the early stages of recovery an increased incidence of theta and delta activity was observed. The recovery records contained a low voltage alpha rhythm and responded to photic stimulation. The literature on this subject is reviewed and the possible modes of pathogenesis are discussed. The authors conclude that such examples of alpha-pattern coma are the result of diffuse cerebral damage and might be detected more frequently in comatose patients who survive if these patients are studied earlier in their clinical course with EEGs.     

The usefulness of EEG, exogenous evoked potentials, and cognitive evoked potentials in the acute stage of post-anoxic and post-traumatic coma

Three-modality evoked potentials (TMEPs) have been used for several years in association with the EEG as a diagnostic and prognostic tool in acute anoxic or traumatic coma. Cognitive EPs have been recently introduced. EEG and cognitive EPs provide functional assessment of the cerebral cortex. TMEP parameters can be described by two indices: the index of global cortical function (IGCF) and the index of brainstem conduction (IBSC). Although it remains a unique tool for epilepsy assessment, the value of EEG is largely limited by its high sensitivity to the electrical environmental noise, its dependence on sedative drugs, and its inability to test the brainstem. Major TMEP alterations (absence of cortical activities more than 24 hours after the onset of post-anoxic coma, major pontine involvement in head trauma) are associated in all cases with an ominous prognosis (death or vegetative state). However, even if mild TMEP changes are associated with a good prognosis in 65% (post-anoxic coma) to 90% (head trauma) of cases, some patients never recover despite exogenous TMEPs that are only mildly altered in the acute stage. Thus, cognitive EPs can usefully complement exogenous EPs as a prognostic tool in coma. Indeed, even if the absence of cognitive EPs in comatose patients does not have any prognostic value, their presence implies a very high (more than 90%) probability of consciousness recovery. The major technical challenge for the future will be the development of reliable tools for continuous EEG and TMEP monitoring.     

Radiological and neurophysiological changes in Japanese encephalitis.

Six patients with Japanese encephalitis, four males and two females whose age ranged between 2 and 47 years, were subjected to neurophysiological and radiological studies. An EEG in five of the patients showed diffuse delta wave activity and one had an alpha coma. Delta activity seems to be due to thalamic involvement, which was seen on CT of two and MRI of all the patients. The thalamic lesions were characteristically bilateral and were haemorragic in five. Changes on MRI included abnormalities of the brainstem in three and the basal ganglia and spinal cord in one patient each. Lower motor neuron signs were present in three patients but abnormal MRI signals in the spinal cord were present in only one out of three patients in whom spinal MRI was carried out. Central motor conduction time in the upper limb was prolonged in three patients (five sides) and in the lower limbs in one (both sides), which was consistent with involvement of the cerebral cortex, thalamus, brainstem, and spinal cord. Changes in MRI and EEG in the acute stage may provide early diagnostic clues in patients with Japanese encephalitis.     

Physiologic and prognostic significance of "alpha coma".

A patient with posthypoxic "alpha coma" is described whose EEGs were recorded before coma, within two hours following the onset of coma and after recovery. The differences observed between the alpha activity during coma and that seen before and after suggest that the alpha activity during coma and the physiologic alpha rhythm are different phenomena. This case, as well as others reported, also suggests that "alpha coma" resolving in the first 24 hours following hypoxia may have a better prognosis than "alpha coma" detected after the first day, and stresses the need for EEG monitoring begun in the immediate period following hypoxia in order to assess accurately the prognostic significance of this EEG pattern in the early stages of postanoxic encephalopathy. The aetiology of "alpha coma" also affects outcome. The survival rate appears higher in patients with respiratory arrest than in those with combined cardiopulmonary arrest.     

Anoxic-ischemic alpha coma: prognostic significance of the incomplete variant

Abstract. The prognostic significance of post-anoxic-ischemic alpha coma (AC) is controversial. We recorded somatosensory evoked potentials (SEPs) and performed serial electroencephalography (EEG) in a 60-year-old woman in coma after cardiac arrest. The first EEG was recorded after 48 hours (GCS=5; E1-V1-M3); brain-stem reflexes were preserved. The EEG pattern showed monotonous alpha frequencies (10–11 Hz) with posterior predominance; acoustic and noxious stimuli evoked EEG reactivity. Early cortical SEPs (72 h) were normal. On the fifth day (GCS=8; E4-V1-M3), the EEG alpha pattern was replaced by a diffuse delta activity; rhythmic theta changes appeared spontaneously or in response to stimuli. The patient regained consciousness on the tenth day and EEG showed posterior theta activity (6–7 c/s) partially reactive to stimuli. At the 6-month follow-up, cognitive evaluation showed mild dementia. Recent studies identified two forms of AC. Patients with complete AC have an outcome that is almost invariably poor. Conversely, incomplete AC (posteriorly accentuated alpha frequency, reactive and with SEPs mostly normal) reflects a less severe degree of anoxic-ischemic encephalopathy. The case we report should be classified, according to the SEPs and EEG features, as incomplete AC. The fact that the patient has regained consciousness, even if with residual cognitive impairment, confirms the need to distinguish this variant from complete AC.     

A reappraisal of rhythmic coma patterns in children

OBJECTIVE: This study was designed to determine the prevalence of rhythmic coma patterns in comatose children and to ascertain the prognostic significance of reactive rhythmic coma patterns. METHODS: We retrospectively analyzed and classified electroencephalogram (EEGs) in comatose children between two months and 18 years of age during the period 1996 - 2003 according to modified Young's classification. Outcome at one-year was scored according to the Paediatric Cerebral and Overall Performance Category Scale. Outcomes were compared using Fisher's exact test and Mann-Whitney test. RESULTS: Analysis of 63 electroencephalogram (EEG) records in 38 patients showed rhythmic patterns in 19 records (30.2%; 9 alpha, 4 spindle, 4 theta and 2 beta coma patterns, total number of children = 14). Aetiology and outcome of alpha coma patterns and other rhythmic coma patterns were similar. In five children, one type of rhythmic pattern changed to another. Records with reactive rhythmic coma 66.7% (6/9), were associated with favourable outcome. Sixty percent of the records (6/10 records in seven children) with non-reactive pattern were associated with unfavourable outcome. This clinically significant difference did not reach statistical significance (lower Paediatric Cerebral and Overall Performance Category Scale score p= 0.14; favourable outcome p=0. 19). CONCLUSION: Rhythmic coma patterns in comatose children are not uncommon. Aetiology, reactivity and outcome of individual patterns are similar and thus make the rhythmic coma patterns distinct EEG signatures in comatose children. There was a clinically significant better outcome with reactive rhythmic coma patterns.     

EEG and Seizure Outcome After Epilepsy Surgery

Summary: The significance of the EEG after epilepsy surgery is not fully understood. We investigated the as- sociation between postoperative EEG abnormalities and persistent seizures after epilepsy surgery as they relate to pathologic lesions. Among 254 patients who underwent epilepsy surgery between 1987 and 1991, we identified 78 patients who had mesiotemporal sclerosis (MTS) and 47 patients who had low-grade brain tumors, all of whom had 6-to 18-month postoperative follow-up including EEG. Patients who had other pathology, multiple operations, callosotomy, or hemispherectomy, or who were aged <18 years or who had insufficient EEG data, were excluded. Patients were classified as having persistent seizures or being seizure-free since operation. EEG abnormalities were abstracted from EEG reports 6–18 months postoperatively. Seizures persisted in 24% of the MTS group and in 27% of the tumor group. Of those with normal EEGs, none of the MTS patients and only 1 of the tumor patients had persistent seizures (p = 0.03 for MTS and p = 0.42 for tumor). Epileptiform discharges and focal slowing were associated with seizure persistence in both groups, but to a significant extent only in the MTS group. In the MTS group, patients who had both epileptiform discharges and focal slowing were more likely to have persistent seizures than were those with either abnormality alone.     

Correlation between diffuse EEG abnormalities and cerebral atrophy in senile dementia.

Thirty-five elderly patients were investigated because of clinical signs of dementia. The presence or diffuse cerebral atrophy, and its severity, were determined by the use of computed tomography (CT scan). All of the patients were also examined by electroencephalography (EEG), and the presence of diffuse abnormalities, especially diffuse slowing, was noted. Specifically, patients with normal or near-normal EEGs were compared with those with severe diffuse slowing. No correlation between the presence or severity of diffuse EEG abnormalities and the degree of cerebral atrophy as measured by CT scan was found. Though the EEG is clearly identifying physiological dysfunction of nerve cells in demented patients it does not appear to be reliable tool for the prediction of diffuse cerebral atrophy in this population.     

Failure of electroencephalography to diagnose brain death in comatose children.

Two isoelectric electroencephalograms obtained 24 hours apart support a clinical diagnosis of brain death in prolonged coma. Without documentation of electrocerebral silence, physicians are reluctant to discontinue vital support systems. A radionuclide bolus technique has been developed that documents the absence of cerebral blood flow in suspected brain death and supplements the flat EEG. In a recent review of this technique, all 27 adults who had EEG activity maintained the integrity of their cerebral blood flow. This contrasts to our studies of 5 children, all of whom demonstrated persistent EEG activity but had no evidence of cerebral blood flow by either the isotope bolus technique (5 patients) or cerebral angiography (4 patients). These children (mean age, 7 months) lacked cephalic reflexes and were maintained on assisted ventilation for an average of 15 days. Multiple electroencephalographic tracings persistently demonstrated low-voltage cortical activity over this time. Despite the lack of cerebral blood flow, all patients were continued on respiratory support. At autopsy, extensive brain liquefaction necrosis was noted. In comatose children, EEG monitoring may be of limited value while cerebral blood flow measurements can provide more practical and prognostic information.     

EEG in the differential diagnosis between Alzheimer''s disease and vascular dementia

Demented patients with Alzheimer's disease (AD) (n = 67), multi-infarct dementia (MID) (n = 77) and probable vascular dementia (PVD) (n = 45) were studied with electroencephalography (EEG). All patients underwent a routine EEG examination and quantitative EEG was recorded from 14 patients with AD, 20 with MID, and 12 with PVD. The patient groups did not differ in regard to sex, age, education, or degree of dementia. Diffuse abnormality of EEG increased in AD, while driving response to photic stimulation and the mean frequency of background activity decreased in all groups with increasing degree of dementia. In quantitative EEG, the percentage of alpha power decreased and those of theta and delta power increased relative to the degree of dementia. Focal abnormalities, and irritative (spikes and/or sharp waves) and slow wave paroxysms were more common in MID than in AD. Patients with different types of dementia did not differ significantly in regard to diffuse abnormality, occurrence of driving response, mean background frequency, or parameters of quantitative EEG. The mean frequency of background activity and the degree of diffuse abnormality correlated with central and cortical atrophy, white matter low attenuation seen on computed tomography, and with neuropsychological findings.     

EEG in the prognosis of toxic coma: reflections apropos of unusual data

During acute intoxications, the first EEG may show persistence or abolition of cerebral activity, but the possibility of recovery after isoelectric tracing in toxic comas must be emphasized. EEG patterns frequently suggest the probability of hypnotic tranquilizer poisoning; 4 types of EEG are encountered corresponding to different grades of toxic coma. Recurrent periods of electrical silence alternating with bursts of activity are habitually recorded in carus comas with hypothermia due to acute barbiturate intoxication, with good prognosis. The possibility of a neurological disturbance associated with drug overdose must be raised whenever an asymmetric tracing is encountered. Serial recordings may detect complications such as: a localized lesion, anoxia or, very rarely, typical paroxysmal abnormalities reappearing in comitial patients before emergence from a toxic coma. Paradoxical monomorphic delta activity corresponding to improvement must not be considered as an aggravation. Peculiar EEG findings occur after oral trichlorethylene poisoning, with temporary clinical deterioration and intermittent periods of electrical silence; recovery is possible. An alpha-like pattern after cardiac arrest of toxic origin has a poor prognosis. The appearance of alternating patterns suggests the development of irreversible brain damage.