Physiologic and prognostic significance of "alpha coma"

Alpha coma EEG pattern in patients with severe COVID-19 related encephalopathy

OBJECTIVE

Encephalopathy is a major neurological complication of severe Coronavirus Disease 2019 (COVID-19), but has not been fully defined yet. Further, it remains unclear whether neurological manifestations are primarily due to neurotropism of the virus, or indirect effects, like cerebral hypoxia.

METHODS

We analysed the electroencephalograms (EEGs) of 19 consecutive patients with laboratory-confirmed COVID-19, performed at peak disease severity as part of their clinical management. Disease severity, respiratory failure, immune and metabolic dysfunction, sedation status, and neurological examination on the day of the EEG were noted.

RESULTS

Severe encephalopathy was confirmed in 13 patients, all with severe COVID-19; 10 remained comatose off sedation, and five of them had alpha coma (AC). Disease severity, sedation, immune and metabolic dysfunction were not different between those with AC and those without.

CONCLUSIONS

Severe COVID-19 encephalopathy is a principal cause of persisting coma after sedation withdrawal. The relatively high incidence of the rare AC pattern may reflect direct SARS-CoV-2 neurotropism with a predilection for the brainstem ascending reticular system.

SIGNIFICANCE

Systematic early EEG detection of encephalopathy related to severe COVID-19 is important for the acute care and the management of long-term neurological and cognitive sequelae, and may help our better understanding of its pathophysiology.

Nonlinear EEG parameters of emotional perception in patients with moderate traumatic brain injury, coma, stroke and schizophrenia

Objective

The aim of this study was to determine the EEG changes induced by emotional non-verbal sounds using nonlinear signals' features and also to examine the subjective emotional response in patients with different neurological and psychiatric disorders.

Methods

141 subjects participated in our study: patients after moderate TBI, patients in acute coma, patients after stroke, patients with schizophrenia and controls. 7 types of emotionally charged stimuli were presented. Non-comatose participants were asked to assess the levels of experienced emotions. We analyzed fractal dimension, signal's envelope parameters and Hjorth mobility and complexity.

Results

The Hjorth parameters were negatively correlated with irritation. The fractal dimension was positively correlated with arousal and empathy levels. The only presentation of laughter to post-stroke patients induced the reaction similar to the control group.

Conclusions

The results showed that the investigated nonlinear features of resting state EEG are quite group-specific and also specific to the emotional state.

Significance

The investigated features could serve to diagnose emotional impairments.

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 and electroencephalographic correlates of acute encephalopathy

The term encephalopathy encompasses a wide variety of syndromes caused by a large number of different toxic, metabolic, and degenerative derangements. Despite advances in intensive medical care and new diagnostic procedures, encephalopathy remains a frequent and underrecognized critical medical condition with high morbidity and mortality. Electroencephalography (EEG) enables rapid bedside electrophysiological measurements of brain dysfunction and complements clinical and neuroimaging assessment of encephalopathic patients. Both progressive slowing of EEG background activity with increasing cerebral compromise and decreased EEG reactivity to external stimuli provide important diagnostic and prognostic information. The aim of this review was to provide an overview of the diagnostic and prognostic value of EEG in encephalopathic patients.

Cortical sources of EEG rhythms in congestive heart failure and Alzheimer's disease

INTRODUCTION

The brain needs continuous oxygen supply even in resting-state. Hypoxia enhances resting-state electroencephalographic (EEG) rhythms in the delta range, and reduces those in the alpha range, with a pattern similar to that observed in Alzheimer's disease (AD). Here we tested whether resting-state cortical EEG rhythms in patients with congestive heart failure (CHF), as a model of acute hypoxia, present frequency similarities with AD patients, comparable by cognitive status revealed by the mini mental state examination (MMSE).

METHODS

Eyes-closed EEG data were recorded in 10 CHF patients, 20 AD patients, and 20 healthy elderly subjects (Nold) as controls. LORETA software estimated cortical EEG generators.

RESULTS

Compared to Nold, both AD and CHF groups presented higher delta (2-4Hz) and lower alpha (8-13Hz) temporal sources. The highest delta and lowest alpha sources were observed in CHF subjects. In these subjects, the global amplitude of delta sources correlated with brain natriuretic peptide (BNP) level in the blood, as a marker of disease severity.

CONCLUSIONS

Resting-state delta and alpha rhythms suggest analogies between the effects of acute hypoxia and AD neurodegeneration on the cortical neurons' synchronization.

SIGNIFICANCE

Acute ischemic hypoxia could affect the mechanisms of cortical neural synchronization generating resting state EEG rhythms, inducing the "slowing" of EEG rhythms typically observed in AD patients.

Impaired Percent Alpha Variability on Continuous Electroencephalography Is Associated with Thalamic Injury and Predicts Poor Long-Term Outcome after Human Traumatic Brain Injury

Continuous electroencephalography (cEEG) is potentially useful in determining prognosis in patients with traumatic brain injuries (TBI). The objective of this prospective, observational cohort study was to determine if the percent alpha variability (PAV) on cEEG was predictive of outcome following TBI. Injury characteristics were indexed to assess whether lesions in specific cerebral loci were correlated with PAV and patient recovery. Fifty-three TBI patients were studied using cEEG recording and serial neuroimaging. Clinical recovery was assessed at regular intervals in hospital and following discharge. The principal outcome measures included the mean 3-day PAV score, the 7-day PAV pattern, delineation of the anatomical sites of brain injury, and the 6-month clinical outcome, as measured by the Glasgow Outcome Scale (GOS). Significant univariate (p = 0.030) and multivariate (p = 0.008) relations were identified between PAV and GOS scores. PAV offered good discrimination between favorable and unfavorable 6-month outcomes (AUC 0.76) and, with a cutpoint of 0.20, had a sensitivity of 87% and negative predictive value of 82%. Multivariate modeling revealed that injuries of the thalamus (p = 0.009) and basal ganglia (p = 0.016), and the presence of diffuse edema (p = 0.009), were the key anatomical predictors of PAV. Brainstem injuries (p = 0.020) and indicators of diffuse cerebral trauma, such as deep white matter shearing (p = 0.036) and multiple subcortical lesions (p = 0.033), were the principal determinants of 6-month recovery. Inclusion of PAV enhanced the accuracy of prediction models that encompassed a selective combination of clinical and anatomical variables (adjusted R(2) = 0.458, p < 0.001). The two main results of this study are (1) PAV is a sensitive predictor of 6-month clinical outcomes following TBI, and (2) injury to the thalamus is related to impaired PAV. PAV appears best utilized as a functional adjunct to traditional clinical and anatomical predictors.

The interpretation of the EEG in stupor and coma

This review discusses a variety of causes of stupor and coma and associated electroencephalographic (EEG) findings. These include metabolic disturbances such as hepatic or renal dysfunction, which are often characterized by slowing of background rhythms and triphasic waves. Hypoxia and drug intoxications can produce a number of abnormal EEG patterns such as burst suppression, alpha coma, and spindle coma. Structural lesions, either supra- or infratentorial, are reviewed. EEGs in the former may show focal disturbances such as delta and theta activity, epileptiform abnormalities, and attenuation of faster frequencies. In infratentorial lesions, the EEG may appear normal, particularly with a pontine lesion. Some patients may be encephalopathic because of ongoing epileptic activity with minimal or no motor movements. This entity, nonconvulsive status epilepticus (NCSE), is difficult to diagnose in obtunded/comatose patients, and an EEG is required to verify the diagnosis and to monitor treatment. Several EEG patterns and their interpretation in suspected cases of NCSE such as periodic lateralized epileptiform discharges (PLEDs), bilateral independent periodic lateralized epileptiform discharges (BIPLEDs), generalized periodic epileptiform discharges (GPEDs), and triphasic waves are reviewed. Other entities discussed include the locked-in syndrome, neocortical death, persistent vegetative state, brainstem death, and brain death.

Emergent EEG is helpful in neurology critical care practice

OBJECTIVE

Emergent EEG (eEEG) is increasingly used in critical care practice related to neurological disorders although it involves considerable reorganization in the neurophysiology department at high cost. There is little data regarding the usefulness of eEEG in acute care situations. Our objective was to audit the practice and utility of eEEG in critical care practice in a developing country.

METHODS

This study was carried out in a tertiary care neurological center situated in a developing country. We had defined eEEG as any EEG performed on a non-elective basis upon request from a clinician for a seemingly emergency indication. All eEEGs performed in the neurophysiology service between October 2002 and September 2003 were reviewed. Referral diagnosis, delay in execution, final diagnosis and outcome were analyzed. eEEG was classified as useful if it clinched a diagnosis, excluded a specific diagnosis or helped in management. Statistical analysis was performed using the chi2 test or Fisher's exact test when indicated. The referral diagnosis and eEEG characteristics were correlated with the utility of the eEEG. Those with P-value <0.05 were considered significant.

RESULTS

There were 286 eEEGs (males 160, mean age 40.6 +/- 23.5 years) among 2798 EEGs (10.2%) performed in the service. eEEG was performed within 24 h in 241 instances and the mean interval from request to formal reporting was 1.13 days. In 62.1% instances eEEG was classified as useful. Usefulness varied according to the referral diagnosis: status epilepticus (n = 41, 100% useful; P = 0.000), brain death (n = 28, 100% useful; P = 0.000), nonconvulsive status (n = 54, 96.3% useful; P = 0.000), recurrent seizures (n = 42, 81% useful; P = 0.006), hypoxic encephalopathy (n = 36, 80.6% useful; P = 0.016), encephalitis (n = 63, 42.9% useful; P = 0.001), metabolic encephalopathy (n=64, 37.4% useful; P = 0.000) and acute demyelination (n = 20, 25% useful; P = 0.001). eEEG findings included epileptiform discharges (n=58), periodic lateralized epileptiform discharges (n=27), discrete seizures (n = 28), nonconvulsive status (n = 12), status epilepticus (n = 8), triphasic waves (n = 15), generalized suppression (n = 22), burst suppression (n = 9), alpha-theta coma (n = 7), electro cerebral silence (n = 2), focal and generalized slowing (n = 172), focal and generalized nonspecific dysfunction (n = 87), and no abnormalities (n = 24). Only discrete seizures (P = 0.000), nonconvulsive status (P = 0.004), generalized suppression (P = 0.004) epileptiform discharges (P = 0.047), and alpha-theta coma pattern (P = 0.047) were significantly correlated with usefulness.

CONCLUSIONS

eEEG provided data that influenced clinical decision-making in the setting of epilepsy related situations, hypoxic encephalopathy and brain death examination.

SIGNIFICANCE

eEEG can provide useful information in selected clinical situations in neurological critical care. The service needs to be called upon judiciously in order to improve the efficacy of this service.

Incomplete alpha coma pattern in a child

Only 19 cases of alpha coma pattern in the pediatric age group had been reported. Recently the concept of reactivity has been included in the definition of alpha coma. Electroencephalography reveals reactivity to painful stimuli in incomplete alpha coma. In adults, this pattern has a better prognosis than the complete pattern with no reactivity. A 5-year-old child had coma secondary to hypoxic brain damage after surgery. His electroencephalogram documented an incomplete alpha coma pattern. He remained in a vegetative state. This study is the first report of a child with incomplete alpha pattern documented on electroencephalogram.

Postanoxic alpha (theta) coma: a reappraisal of its prognostic significance

OBJECTIVES

To appraise the controversial prognostic significance of postanoxic alpha or theta coma (ATC).

METHODS

We prospectively assessed 14 comatose patients with ATC after cardiac arrest by means of a protocol which included repeated clinical examinations, EEG, and median somatosensory evoked potentials (SEP). Good outcome was defined by the reappearance of cognition (Glasgow outcome scale 3-5) at any time during the 1 year follow-up.

RESULTS

Nine of 14 patients had a monotonous, frontally accentuated and a reactive alpha (theta) EEG activity (complete ATC). In these patients ATC was recorded a mean of 47 h after resuscitation, the mean Glasgow coma scale (GCS) was 4 at 48 h, and early cortical SEPs were altered or absent in 5 of 7 patients. All nine patients died. In five of 14 patients the alpha (theta) EEG activity was either not monotonous, partially reactive or posteriorly dominant (incomplete ATC). In these patients ATC was recorded a mean of 43 h after resuscitation, the mean GCS was 8 at 48 h, and early cortical SEP were normal in 4 of 5 patients. Three of 5 patients regained cognition, two of them remained however dependent in activities of everyday life.

CONCLUSIONS

This study and a review 283 cases of postanoxic ATC reported in the literature suggest the existence of incomplete and complete variants of postanoxic ATC. Whereas complete ATC is invariably associated with a poor outcome, full recovery is possible in patients with incomplete ATC. The combination of EEG, clinical, and SEP findings improves the prognostic accuracy of postanoxic ATC.

Etiology, neurologic correlations, and prognosis in alpha coma

OBJECTIVE

To determine the factors affecting prognosis in alpha coma (AC).

METHODS

Retrospective review of 36 study patients, 36 control coma patients matched for age and etiology, and meta-analysis of 335 cases in the world literature.

RESULTS

Principal causes were cardiorespiratory arrest (CRA) (21 patients); infection, metabolic dysfunction, head trauma (3 each); and drugs, stroke and hypoxia (2 each). Outcome was predicated by EEG reactivity to noxious stimuli. Fourteen of the 15 patients with reactive EEGs, had measurable outcome, 8 awoke - all but two had etiologies other than CRA. Fourteen of 19 patients without EEG reactivity died; two had support discontinued and 3 awoke. Following CRA, 16/21 patients died and 3 had support discontinued. Only 3 patients made a good recovery - all with toxic or metabolic etiologies. Literature meta-analysis of 335 cases showed that overall, AC carried a poor prognosis (76% died). CRA (226 cases) had an 88% mortality; strokes (29 cases), a 90% mortality; hypoxia without cardiac arrest (28 cases), a 61% mortality; drug-induced AC (25 cases), an 8% mortality.

CONCLUSIONS

Although the cause of AC largely predicts outcome, EEG reactivity in AC predicted survival: most patients with reactivity awoke; most of those without, died. Few survivors had meaningful recovery.

EEG in Japanese encephalitis: a clinico-radiological correlation

This study was undertaken due to the paucity of studies on electroencephalographic (EEG) changes in Japanese encephalitis (JE) and their clinical and radiological correlation. Twenty seven patients with JE were included whose age ranged between 2 and 54 years, 8 of whom were females and 10 aged 12 or less. On admission, Glasgow coma scale (GCS) ranged between 4 and 9. Seizures were present in 9 patients which were generalised tonic clonic in all except one who had partial motor seizure. Behavioural abnormalities were present in 3 patients. Three patterns of EEG were noted which included diffuse continuous delta in 21, diffuse delta with spikes in 3; and nonmodulating non responsive alpha activity ('alpha pattern' coma) in 3 patients. The background EEG activity became normal in all at 3 months although seizure activity was noted in 3 patients. MRI or/and CT scan revealed bilateral thalamic involvement in all, pons in 2, midbrain in 7, basal ganglia in 5, cerebral cortex in 4 and white matter oedema in 5 patients. Five patients died in the acute stage and 3 patients lost from follow-up. At 3 months, 7 patients had complete, 6 partial and 6 poor recovery. The EEG pattern did not correlate with the GCS and outcome. In JE, EEG reveals non-specific delta showing in acute stage and 'alpha pattern' coma may be a more common presentation than realised and does not always predict a poor outcome.

Comparison between the alpha pattern in normal subjects and in alpha pattern coma

Alpha pattern coma (APC) is an uncommon clinical EEG pattern in comatose patients, most commonly in association with anoxic-ischemic encephalopathy after cardiac arrest. Despite the pattern's striking similarity to that of the normal awake EEG, there are theoretical and experimental reasons for believing that the two rhythms result from different processes. The analysis of quantitative differences in APC from normal rhythms requires computer analysis. Because most cases of this rare entity have been collected over the years on paper traces, computer analysis appears implausible. In a companion article, we describe a method to quantify sections of paper EEGs. We applied this method to EEGs of five APC patients and five normal controls and noted a significant difference in the coherence between the two hemispheres in the alpha range. This finding is in keeping with theoretical, experimental, and clinical observations suggesting that APC may result from significant thalamo-cortical disruption.

Alpha rhythms as physiological and abnormal phenomena

There are three physiological alpha rhythms in mature healthy humans: (a) the classical posterior alpha; (b) the Rolandic mu rhythm and (c) the midtemporal 'third rhythm'. The classical posterior alpha rhythm develops out of a 4/s rhythm appearing at age 4 months and gradually reaches the alpha frequency band around age 3 years. The mature frequency around 10/s is subject to subtle physiological changes and grossly decelerates in the face of pathology. No posterior alpha rhythm may be detectable in a minority of healthy adults with an inherited low voltage fast EEG. One is tempted to speculate that these individuals may have a hidden alpha rhythm in neuronal level and defective mechanisms of synchronization. Alpha blocking with visual stimuli (eye opening) is a classical response; responses to mental stimuli (mental arithmetic) are inconsistent, presumably due to the involvement of higher cognitive functions. The Rolandic my rhythm is found with scalp EEG in a minority of subjects but there is good reason to presume that all healthy adults have this rhythm. A particularly powerful mu rhythm reaches the scalp but this could be also an indicator of a mild CNS dysfunction. There is even a relationship between mu rhythm and the central spike activity in children with benign Rolandic epilepsy. The midtemporal third rhythm is not detectable in the scalp EEG unless there are local bone defects. Its functional significance is debatable; its blocking responses encompass various higher cognitive tasks and are inconsistent; responses to auditory stimuli do occur but appear to be of secondary significance. This rhythm arises from midtemporal structures which by far exceed the borders of the auditory cortex. Abnormal rhythmical alpha activity-above all the alpha coma in life-threatening cerebral anoxia -is discussed in order to deepen our understanding of the physiological alpha rhythms. Severe cortical de-afferentation may give rise to cortical autorhythmicity-either in alpha frequency or in other frequency bands. Physiological alpha rhythms are likely to have closer relationships to 'events' than one might have thought earlier. The demonstration of event-related desynchronization and synchronization (in Pfurtscheller's work) clearly underscores this view.

Periodic complexes, absence-like status and suppression-burst pattern in coma following cardiorespiratory arrest

A 75-year-old man suffered a cardiac arrest and severe anoxic encephalopathy. A serial study of electroencephalograms during 4 days showed sequential changes from periodic approximately 2 Hz spike activity to absence-like status (ALS) and then into a suppression-burst pattern. Intravenous administration of phenytoin had no effect on ALS. A small dose of intravenous diazepam reduced a suppression-burst pattern. We speculate that the ALS originates in the midline structures, spreading bilaterally and synchronously to the "dysfunctional" cortex; the sustained discharges were a manifestation of associated reticular lesions, and we believe that intravenous diazepam suppressed the spread of ALS to the "dysfunctional cortex," leading to the appearance of the suppression-burst pattern. The only limitation for definitive conclusions may be a lack of postmortem verification. Autopsy findings, however, could not have confirmed the dynamic changes that occurred during the 5 days before the patients death.

Alpha, theta and alpha-theta coma: a clinical outcome study utilizing serial recordings

Alpha coma (AC), theta coma (TC) and alpha-theta coma (ATC) are transient clinical-electroencephalographic phenomena which do not differ from each other in etiology or outcome and are indicative of a severe disturbance in thalamo-cortical physiology. Although most patients do poorly, these patterns are not reliably predictive of outcome, regardless of etiology. We found that AC, TC or ATC usually change to a more definitive pattern by 5 days from coma onset. EEG reactivity in subsequent patterns is relatively favorable, while a burst-suppression pattern without reactivity is unfavorable in anoxic-ischemic encephalopathy.

Development of a novel EEG rating scale for head injury using dichotomous variables

We developed a new EEG rating scale for electrographic assessment of head injured patients. Phenomena present in posttraumatic EEG were scored as dichotomous variables (present or absent). These phenomena included background activity (alpha, beta, theta, delta), sleep spindles, focal abnormalities, reactivity and variability, epileptiform activity, and specific comatose patterns. Each variable was weighted according to its perceived prognostic value: i.e., normal alpha 10, flat EEG -10, spindles 4, etc. Combinations of possible scores ranged from +23 to -10. Fifty-seven EEGs from different head injured patients were independently and retrospectively analyzed by two investigators. There was a high correlation for intra- (r = 0.95) and inter- (r = 0.85) observer rating using the dichotomous test. When patients with scores over 15 (i.e., with reactive alpha) and patients with scores of -10 (i.e., ECI records) were excluded, the intra-rater and inter-rater correlations were still high (0.81 and 0.76, respectively). There was a high correlation between Glasgow outcome score at discharge and the dichotomous EEG score. This EEG scale scores most major categories of EEG activity, utilizes a multipoint scale for correlation purposes, and allows data to be analyzed in sub-categories (i.e., spindles in coma). The separate weighting score allows for refinement of the scale after data collection (i.e., to fit prospective outcome). We feel that this scale is reproducible and valid, and may be applicable to other patient groups with severely altered EEGs.

Rhythmic coma in children

We describe a syndrome of rhythmic coma in children that consists of an invariant, nonreactive, diffuse cortical activity of a specific frequency, such as alpha, beta, spindle, or theta, recorded from a comatose child. We report 11 cases of children who were found to be in rhythmic coma during their acute illnesses. Their ages ranged from 2 to 15 years, and their diagnoses included encephalitis, head trauma, seizures, near drowning, brain tumors, stroke, and metabolic derangements. The specific frequency of the electroencephalographic pattern, ie, alpha, beta, spindle, or theta, did not influence the outcome. The clinical outcome appeared to depend on the primary disease process rather than the electroencephalographic finding. The prognosis of alpha-frequency rhythmic coma as well as of rhythmic coma in general was better in children than in adults. The pathophysiology in children may be similar, ie, the interruption of reticulothalamocortical pathways by metabolic or structural abnormalities, but the expression of this deafferentation may be more varied in the developing brain. Thus, we propose the term rhythmic coma as a unified concept for alpha, beta, spindle, and theta coma in children.

[Persistent alpha-vegetative state]

After briefly reviewing the concepts of "coma" and "alpha-coma", we report the case of a patient with presumable Pick's disease who spent several weeks in a vegetative state with a normal and reactive EEG in the alpha range in the later stages of her illness. We (a) emphasize some implications of the appearance of the eyes in such patients, b) stress the importance of distinguishing alpha activity from true alpha rhythm and (c) suggest the category "alpha-coma" should include only those individuals bearing evidence of disorders of the junctional tegmentum of the pons and midbrain. In a complementary way, we propose that patients in a persistent vegetative state displaying normal EEG should be separately classified as persistent "alpha-vegetative state".

Alpha coma

Six personal cases of alpha coma are reported: 3 following a cerebrovascular accident and 3 resulting from cerebral concussion. Two patients survived. On the basis of differences in pathogenesis, EEG characteristics and prognosis, the following classification is proposed: alpha coma resulting from brain stem vascular accident; cerebral concussion; diffuse cerebral hypoxia; drug intoxication. The clinical course of each of the classes of alpha coma is outlined. The alpha coma state is not restricted to cases with structural brain stem lesions c.q. lesions of the pontomesencephalic region.

Prognostic and neurophysiological implications of concurrent burst suppression and alpha patterns in the EEG of post-anoxic coma

Concurrent burst suppression and alpha pattern coma developed in the EEG of a 2-year-old child who suffered a cardiac arrest secondary to hypoxemia from Haemophilus influenza epiglottis. The neurophysiological implications of this association are discussed and the literature pertaining to the role of barbiturates in the production of post-anoxic coma with an alpha pattern and experimental post-resuscitative alpha frequencies is reviewed.

Recovery from alpha coma after decompression sickness complicated by spinal cord lesions at cervical and midthoracic levels

A modified alpha pattern activity occurred in the EEG of a 21-year-old man during recovery from a diving injury. It persisted for 10 days but finally the EEG became normal. There was clinical and neurophysiological evidence of additional separate lesions in the cervical and mid-thoracic spinal cord. The latter resulted in spastic paraplegia but the patient made an otherwise good recovery.

Unusual EEG patterns in coma, and their evolution

A 23-year-old chronic asthmatic patient is reported who showed successively four different EEG patterns within a 7 day period of unconsciousness following cardio-respiratory arrest. The initial record was dominated by alpha activity, then beta activity supervened, to be followed by spindle components. Finally an isoelectric tracing occurred before death. A computer file search for all cases of unusual EEG coma patterns was carried out. It failed to reveal any other patient with a similar sequence, but various types of evolution were noted. Such features are seen in only a very small percentage of comatose patients, and in the context of cardio-respiratory arrest are almost invariably fatal.

Experimental data on the nature of postresuscitation alpha frequency activity

Synchronized activity of alpha frequency recorded from a number of dog brain formations in the initial stages of postischaemic (postresuscitation) restoration was studied. Using the methods of destruction and elimination it was shown that the amygdaloid nuclei were the main source of such activity. Analysis of the general and particular coherence functions at the frequencies of alpha-like activity has shown that subcortical formations (thalamus, nucleus caudatus) become secondarily active sources of the generation of the bursts and of their generalization in the brain. Investigations and available literature lay the basis for the hypothesis that the activity observed in experiments and the activity described during postresuscitation alpha-pattern coma in humans have similar mechanisms of development and are, probably, identical.

Theta pattern coma, a variant of alpha pattern coma

Electroencephalograms with a dominant rhythmic areactive 5Hz theta activity are reported in two comatose patients with fatal outcome. This pattern was followed by isoelectric EEG and death in the first patient, who suffered multiple injuries including severe cerebral concussion and later tentorial herniation. The second patient died eight hours after the second EEG recording, both EEGs having shown a very rhythmic 5-6 Hz activity which was maximal anteriorly. He died two days after a severe cerebral hypoxic episode due to acute respiratory failure. Both patients were in their late sixties. It is suggested that the dominant areactive theta activity is a variant of malignant "alpha pattern coma".