Generalized, bilaterally synchronous bursts of slow waves in the EEG

Effects of antiepileptic drugs on electroencephalography (EEG): Insights and applicability

OBJECTIVE

The objective of the study was to assess the effects of antiepileptic drugs (AEDs) on posterior alpha rhythm and determine whether they produce pathological slow waves in patients with epilepsy.

METHODS

Outpatient electroencephalographs (EEGs) in alert patients were selected. The three compared groups include 1) patients with an interested AED (monotherapy or combined with other AEDs); 2) patients with AEDs other than the interested AED; and 3) patients who did not take AEDs. Outcomes were frequency of posterior alpha rhythm and presence of generalized continuous (CSWs) and generalized intermittent slow waves (ISWs). Analysis of variance was used to assess which AED was associated with slower posterior alpha rhythm. Chi-square and logistic regression were employed to assess association and odds ratio (OR) with 95% confidence interval (CI) between pathological generalized slow waves and each AED.

RESULTS

Among 1050 EEG tracings, 638 EEGs met our criteria. Electroencephalographs requested because of cognitive decline and psychiatric symptoms were excluded, leaving 616 EEGs for analysis. Four hundred thirty-seven patients received at least one AED, whereas the remaining 179 patients did not take AED. Conventional AEDs [carbamazepine (CBZ), p = 0.024; phenobarbital (PB), p = 0.013; phenytoin (PHT), p = 0.001] except valproic acid (VPA) were associated with slower alpha frequency. Carbamazepine [adjusted OR: 5.74 (95% CI: 2.07, 15.94)] and PB [adjusted OR: 2.58 (95% CI: 1.15, 5.78)] were significantly associated with generalized ISWs. None were associated with generalized CSWs.

CONCLUSIONS

Phenytoin, CBZ, and PB are associated with slower posterior alpha frequency. The latter 2 AEDs also produced pathological generalized ISWs. Valproic acid, benzodiazepines, and new-generation AEDs are not associated with either outcome. The presence of generalized ISWs in patients taking CBZ or PB should be cautiously interpreted since there can be drug effects. Association with cognitive side effects of these slow waves should be further studied.

Frontal Intermittent Rhythmic Delta Activity (FIRDA) in the Neurological Intensive Care: Prevalence, Determinants, and Clinical Significance

INTRODUCTION

Frontal intermittent rhythmic delta activity (FIRDA), a transient rhythmic slow wave pattern over the anterior EEG leads, has been reported in a wide variety of cerebral lesions and different metabolic disturbances. Few authors have analyzed the frequency and clinical significance of FIRDA in the critical care setting. We aimed to better understand these issues in our intensive care cohort and if possible, try to delineate its underlying mechanisms.

METHODS

Video-EEG reports of consecutive adult patients in the neurological intensive care unit (NICU) since 2009 were retrospectively reviewed to identify cases with FIRDA. Demographic, clinical, and laboratory data were obtained from EEG reports and patient charts. Age- and sex-matched patients with acute stroke, hospitalized in NICU and no FIRDA on video-EEG monitoring served as the control group.

RESULTS

Among 162 patients who underwent video-EEG monitoring, FIRDA was documented in 17%. Female prevalence was 50% and age ranged from 23 to 82 years. Twenty-three (82%) of patients with FIRDA had a diagnosis of stroke. Comparison of demographic characteristics, EEG findings, metabolic disturbances and prognoses revealed no differences between stroke cases with and without FIRDA, except for higher frequency of acute and chronic isolated posterior circulation infarcts in patients with FIRDA.

CONCLUSION

FIRDA is more commonly encountered in the neurocritical care setting as compared with outpatient EEG clinics. Our findings in stroke patients indicate that involved vascular territories may be related to the generation of FIRDA.

Advances in dialysis encephalopathy research: a review

Dialysis encephalopathy (DE) is a progressive, fatal disease with a high mortality rate. Understanding the causes of this disease and the efforts to prevent and treat it would help improve the prognosis and quality of life of affected patients. This paper reviews the etiology, clinical features, methods of examining accessory features, diagnosis, treatment, and prevention of DE. We found that DE is likely to be related to aluminum poisoning. The clinical manifestations of DE include language disorders, mental and behavioral disorders, cognitive decline, and movement disorders. Electroencephalogram (EEG) findings mainly consist of an abundance of low waves, intermittent bilateral synchronous high-amplitude spikes, and ridge waves. Assessing the clinical features and obtaining an EEG are of great value in diagnosis, and DE is treated by both reducing aluminum intake and increasing aluminum excretion. Deferoxamine (DFO) is an effective treatment for DE.

Electroencephalography of encephalopathy in patients with endocrine and metabolic disorders

Patients with acute alteration in mental status from encephalopathy because of underlying metabolic-toxic or endocrine abnormalities are frequently seen in the acute hospital setting. A rapid diagnosis and correction of the underlying cause is essential as a prolonged state of encephalopathy portends a poor outcome. Correct diagnosis and management remain challenging because several encephalopathies may present similarly, and further laboratory, imaging, or other testing may not always reveal the underlying cause. EEG provides rapid additional information on the encephalopathic patient. It may help establish the diagnosis and is indispensable for identifying nonconvulsive status epilepticus, an important possible complication in this context. The EEG may assist the clinician in gauging the severity of brain dysfunction and may aid in predicting outcome. This review summarizes the current knowledge on EEG findings in selected metabolic and endocrine causes of encephalopathy and highlights distinct EEG features associated with particular etiologies.

Transient insight induction with electroconvulsive therapy in a patient with refractory schizophrenia: a case report and systematic literature review

Anosognosia or lack of illness awareness is a clinical manifestation of both schizophrenia and right hemispheric lesions associated with stroke, neurodegeneration, or traumatic brain injury. It is thought to result from right hemispheric dysfunction or interhemispheric disequilibrium, which provides a neuroanatomical model for illness unawareness in schizophrenia. Lack of insight contributes to medication nonadherence and poor treatment outcomes and is often refractory to pharmacological and psychological interventions. We present the first report of transient illness awareness (<8 hours) after individual bilateral electroconvulsive therapy treatments in the case of a 39-year-old man with antipsychotic refractory schizophrenia. Electroencephalography demonstrated frontal slow wave activity with shifting frontotemporal predominance, which was concurrent with the patient's transient level of insight. A systematic review of the literature on electroconvulsive therapy-induced illness awareness in schizophrenia and psychotic disorders produced zero relevant results. Future research should focus on the prospective role of focal interventions, such as transcranial magnetic stimulation, in the development of a neurophysiological model for anosognosia reversal in schizophrenia that may, in turn, contribute to novel therapeutic developments targeting lack of illness awareness.

The significance of frontal intermittent rhythmic delta activity in children

OBJECTIVE

To determine the correlation between frontal intermittent rhythmic delta activity (FIRDA) and the clinical and radiological correlates in children.

METHODS

Retrospective review of the EEG and imaging studies of 37 children with documented FIRDA.

RESULTS

FIRDA was associated with multiple neurological conditions and not necessarily with midline lesions. Patients with abnormal neurological exam had a longer FIRDA duration (average 9.5 seconds) compared to children with no reported abnormal examination (average of 6.5 seconds). FIRDA ranged from 2 to 2.5 Hz (n = 15), 3 Hz (n = 17) and from 1.5 to 3 Hz (n = 5) and there was a significant association between the duration of FIRDA and abnormal laboratory tests (p. < 0.05, Student's T test).

CONCLUSION

FIRDA was not correlated with midline brain lesions in children. FIRDA may be a non specific oscillation of an unhealthy pediatric brain with or without seizures.

Safety study of 50 Hz repetitive transcranial magnetic stimulation in patients with Parkinson's disease

OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) has shown promising results in treating Parkinson's disease (PD), but the best values for rTMS parameters are not established. Fifty Hertz rTMS may be superior to 25 Hz rTMS investigated so far. The objective of this study was to determine if 50 Hz rTMS could be delivered safely in PD patients since current safety limits are exceeded.

METHODS

Fifty Hertz rTMS was applied with a circular coil on the primary motor cortex (M1). Stimulation intensity was first tested at 60% rest motor threshold [RMT] and 0.5 s train duration and then increased in 0.5 s steps to 2 s, and by 10% steps to 90% RMT. Multi-channel electromyography (EMG) was recorded to control for signs of increasing time-locked EMG activity including correlates of the spread of excitation and after-discharges, or an increase of M1 excitability. Pre- and post-50 Hz rTMS assessments included EEG, Unified Parkinson Disease Rating Scale (UPDRS), Grooved Pegboard Test, Serial Reaction Time Task (SRTT), Folstein Mini-Mental Status Examination (MMSE) and Verbal Fluency to control for motor and cognitive side effects.

RESULTS

Ten PD patients were investigated. Multi-channel EMG showed no signs of increased time-locked EMG activity including correlates of the spread of excitation and after-discharges, or increased M1 excitability in 9 patients. A PD patient with bi-temporal spikes in the pre-testing EEG had clinical and EMG correlates of spread of excitation at 90% RMT, but no seizure activity. Pre- and post-50 Hz assessment showed no changes. No adverse events were observed. Fifty Hertz rTMS was well tolerated except by 1 patient who wished to terminate the study due to facial muscle stimulation.

CONCLUSION

Fifty Hertz rTMS at an intensity of 90% RMT for 2 s appears safe in patients with PD, but caution should be taken for patients with paroxysmal EEG activity. For this reason, comprehensive screening should include EEG before higher-frequency rTMS is applied.

SIGNIFICANCE

This is the first study to investigate safety of 50 Hz rTMS in humans.

Toward the substitution of invasive electroencephalography in epilepsy surgery

The authors compared the localization accuracy of interictal magnetoencephalography (MEG) with ictal and interictal invasive video electroencephalography (VEEG) in identifying the epileptogenic zone in epilepsy surgery candidates. Forty-one patients, 29 with temporal lobe epilepsy (TLE) and 12 with extratemporal lobe epilepsy (ETLE), participated. Only patients with interictal changes during the MEG recordings were included. A comparison of the accuracy of invasive VEEG and MEG seizure zone identification was based on the degree of overlap between the location of the actual surgical resection and the zone identified by each method, and the success of surgery in reducing seizure activity. No statistical differences were observed between the accuracy of invasive VEEG and MEG in determining the location of the seizure zone across TLE and ETLE cases. Invasive VEEG and MEG localization judgments were correct in 54% and 56% of the cases, respectively. Separate group analyses suggested that MEG may be less beneficial relative to invasive VEEG in ETLE than TLE cases. MEG is of statistically equivalent accuracy to invasive VEEG, despite the fact that its use has not reached optimal conditions. The authors predict the replacement of the more invasive procedure with MEG in the near future for TLE cases, subsequent to the optimization of the conditions under which preoperative MEG is performed.

Clinical correlation of occipital intermittent rhythmic delta activity

Frontal intermittent rhythmic delta activity is associated with encephalopathy, and temporal intermittent delta activity is associated with epilepsy, but the importance of OIRDA (OIRDA) is less well defined. The authors reviewed retrospectively EEGs and medical records of 77 patients with OIRDA to determine whether they had epilepsy, acute encephalopathy, or another diagnosis. They compared the incidence of epilepsy in this population with a control group of 77 patients referred for EEG, matched for age, gender, and year of EEG. OIRDA was most commonly generalized, high amplitude, saw toothed, and reactive to eye opening, and with mean frequency of 2.89 +/- 0.50 Hz. Mean age was 8.1 +/- 4.5 years. Seventy-six of 77 patients were <or= 18 years old. Seizures were present in 69 OIRDA patients but only 41 control subjects (P < 0.0001). OIRDA compared with control subjects had more patients with GTCs (34 vs. 10; P < 0.0001) and absence seizures (25 vs. 6; P < 0.0001), but an equal number had partial seizures (30 vs. 27). Only one OIRDA patient had acute encephalopathy. OIRDA patients with seizures were younger (7.6 +/- 4.7 years vs. 12 +/- 6.9 years; P < 0.01) and more likely to evolve to spike-wave activity compared with OIRDA patients without seizures. OIRDA is present almost exclusively in children and is associated with epilepsy but not acute encephalopathy. OIRDA has clinical importance distinctly different from frontal intermittent rhythmic delta activity.

Occurrence of nonconvulsive seizures, periodic epileptiform discharges, and intermittent rhythmic delta activity in rat focal ischemia

A significant proportion of neurologic patients suffer electroencephalographic (EEG) seizures in the acute phase following traumatic or ischemic brain injury, including many without overt behavioral manifestations. Although such nonconvulsive seizures may exacerbate neuropathological processes, they have received limited attention clinically and experimentally. Here we characterize seizure episodes following focal cerebral ischemia in the rat as a model for brain injury-induced seizures. Cortical EEG activity was recorded continuously from both hemispheres up to 72 h following middle cerebral artery occlusion (MCAo). Seizure discharges appeared in EEG recordings within 1 h of MCAo in 13/16 (81%) animals and consisted predominantly of generalized 1-3 Hz rhythmic spiking. During seizures animals engaged in quiet awake or normal motor behaviors, but exhibited no motor convulsant activity. Animals had a mean of 10.6 seizure episodes within 2 h, with a mean duration of 60 s per episode. On average, seizures ceased at 1 h 59 min post-MCAo in permanently occluded animals and did not occur following reperfusion at 2 h in transiently occluded animals. In addition to seizures, periodic lateralized epileptiform discharges (PLEDs) appeared over penumbral regions in the injured hemisphere while intermittent rhythmic delta activity (IRDA) recurred in the contralateral hemisphere with frontoparietal dominance. PLEDs and IRDA persisted up to 72 h in permanent MCAo animals, and early onset of the former was predictive of prolonged seizure activity. The presentation of these EEG waveforms, each with characteristic features replicating those in clinical neurologic populations, validates rat MCAo for study of acutely induced brain seizures and other neurophysiological aspects of brain injury.

The localization of spontaneous brain activity: first results in patients with cerebral tumors

OBJECTIVE

From EEG studies, it is known that structural brain lesions are accompanied by abnormal rhythmic electric activity. With the better spatial resolution of MEG, MEG dipole analysis can extend the knowledge based on EEG power spectra. This study presents the first results of a completely automatic analysis method applied to spontaneous MEG.

METHODS

Spontaneous MEG data of 5 patients with cerebral brain tumors and 4 controls were collected using a whole-head MEG system. Signals were bandpass-filtered with cut-off frequencies according to standard EEG bands. A moving dipole model was fitted to samples with at least twice the average sample power. Dipoles explaining 90% or more of the magnetic variance were projected onto a matched MR scan.

RESULTS

In controls, dipole distributions are symmetrical with respect to the mid-sagittal plane whereas distributions in patients often are asymmetrical to it. Dipoles describing gamma activity were located contralateral, and dipoles describing delta and theta activity were located ipsilateral to lesions.

CONCLUSIONS

The automatic method gives plausible 3-dimensional information about generator foci of abnormal slow waves and other rhythms with respect to lesion foci and thereby adds physiological knowledge to that derived from EEG power spectra.

Spatio-temporal characterizations of non-linear changes in intracranial activities prior to human temporal lobe seizures

Recent studies have shown that non-linear analysis of intracranial activities can detect a 'pre-ictal phase' preceding the epileptic seizure. Nevertheless, the dynamical nature of the underlying neuronal process and the spatial extension of this pre-ictal phase still remain unknown. In this paper, we address these aspects using a new non-linear measure of dynamic similarity between different parts of intracranial recordings of nine patients with medial temporal lobe epilepsy recorded during transitions to seizure. Our results confirm that non-linear changes in neuronal dynamics allow, in most cases (16 out of 17), a seizure anticipation several minutes in advance. Furthermore, we show that the spatial distribution of pre-ictal changes often involves an extended network projecting beyond the limits of the epileptogenic region. Finally, the pre-ictal phase could frequently (13 out of 17) be characterized with a marked shift toward slower frequencies in upper delta or theta frequency range.

Intermittent rhythmic delta activity (IRDA) morphology cannot distinguish between focal and diffuse brain disturbances

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.

Intermittent rhythmic delta activity (IRDA) in a patient with band heterotopia

We report a patient with band heterotopia whose electroencephalogram (EEG) showed typical morphological features of intermittent rhythmic delta activity (IRDA). This 18-year-old woman had complex partial seizures. Neuropsychometry revealed mental dysfunction. Magnetic resonance imaging (MRI) showed bilaterally symmetrical layer of heterotopic gray matter in deep white matter over the frontal, parietal and occipital regions. This case is the first report of IRDA detected in band heterotopia.

The fundamental neural mechanisms of electroencephalography

We are at an interesting time in the evolution of the EEG. Studies are opening the door to understanding the intrinsic neuronal properties and network operations responsible for the generation of EEG oscillations. I will review some of our knowledge regarding the physiology of the normal and abnormal EEG. Both epileptic and non-epileptic activity will be discussed. Less is known about the latter, because of difficulties in developing appropriate models. The major dichotomy for both types of EEG phenomenon will be focal and generalized (or widespread. Certain distinctive abnormal EEG patterns including burst suppression, periodic phenomena and intermittent rhythmic delta will also be addressed.

The electroencephalogram in acetazolamide-responsive periodic ataxia

Acetazolamide-responsive periodic ataxia (ARPA) is a rare movement disorder, characterized by recurrent episodes of vertigo, cerebellar ataxia, and nystagmus, which has recently been characterized genetically. The pathophysiology is unknown, but it is probably not epileptic. By definition, acetazolamide produces an impressive symptomatic relief. Because of the paroxysmal nature of the disorder, EEG tracings were often obtained. We report four new cases (two familial and two sporadic) with typical ARPA (none of whom had metabolic abnormalities or continuous electrical muscle activity) and review the EEG findings associated with this disorder. EEG findings were reported in 18 kindreds and nine sporadic cases (including ours). EEG was described in 54 of the 140 affected cases and was abnormal in 52% (28/54). Most commonly seen was intermittent generalized slow activity, observed in 35% (19/54), frequently intermingled with spikes (10 cases). Other abnormalities included nonspecific mild generalized or focal slowing in seven (13%) and focal epileptic activity in two (4%) patients. The paroxysmal EEG activity frequently seen in ARPA should not establish a diagnosis of epilepsy. Although not specific, it may suggest the correct diagnosis and indicate treatment with acetazolamide.

EEG findings in acetazolamide-responsive hereditary paroxysmal ataxia

EEG studies were performed in six family members affected by acetazolamide-responsive paroxysmal ataxia. Intermittent rhythmic delta activity was found at rest in five of them; low amplitude spikes were associated with delta waves in two cases, resulting in irregular spike and wave patterns. Slowing of background activity was present in three patients. EEG abnormalities were activated by hyperventilation and modified neither by intermittent photic stimulation, nor by acetazolamide therapy. Our results suggest that EEG may be helpful to recognize this rare, but well defined, treatable disorder.

Frontal intermittent rhythmic delta activity (FIRDA) in pituitary adenoma

We report a case of FIRDA in the EEG of a patient diagnosed as major depression with pituitary adenoma and hyponatremic encephalopathy. The pituitary adenoma appeared to be a major factor responsible for FIRDA in this case. Although other factors associated with this case, i.e., diffuse encephalopathy and administration of antipsychotic drugs, have been reported to be causative, FIRDA remained in the EEG after these other factors diminished. Although size of the pituitary adenoma that might be associated with FIRDA in the EEG recording was not identified in this study, FIRDA may be associated with a small pituitary adenoma less than 10 mm in diameter. We think a diligent search for additional pathology is recommended if FIRDA is seen in the EEG of an otherwise normal patient.

Continuous, generalized, high-voltage fast activity and FIRDA in two children

The EEG pattern of continuous, generalized, high-voltage fast rhythms without any reaction to eye-opening/closure, photic stimulation, or the sleep-awaking cycle was previously reported to be characteristic of infantile neuroaxonal dystrophy (INAD). However, we have observed such fast activity in one child with INAD and one with Menkes' kinky-hair syndrome. They both exhibited severe psychomotor disturbance, and their EEGs also included "frontal intermittent rhythmic delta activity (FIRDA)," a nonspecific EEG finding suggestive of organic encephalopathy. Since the continuous, generalized, high-voltage fast activity had features suggestive of spindles in both children, this EEG pattern is thought to actually represent "extreme spindles," and nonspecifically to indicate widespread organic brain damage.

Discrepancies between CT and EEG findings after acute cerebrovascular disease

Combined EEG and brain CT examinations were performed in 33 patients during the 1st and 2nd week after stroke. CT was abnormal in 17 patients (51%) and EEG was abnormal in 24 patients (72%). In 17 patients CT and EEG showed conflicting results; in 5 patients with normal EEG findings CT was pathological, and 12 patients had normal CT but pathological EEG findings. In this latter group, there were 5 particularly interesting cases with normal CT and a prominent unilateral EEG abnormality. Recently patients with this combination of findings have been described where further investigations disclosed internal carotid occlusion, which could be treated surgically. It is suggested that EEG should be more extensively used when CT findings are negative after stroke, and if a major unilateral EEG abnormality is encountered in such cases, further investigations with angiography should be considered in order to exclude surgically treatable internal carotid occlusion.

Nonepileptogenic epileptiform electroencephalographic activity

Accumulated experience has delineated numerous distinctive electroencephalographic (EEG) patterns that are morphologically epileptiform but have no relationship to the process responsible for generating epileptic seizures and have little or no practical value for diagnosis. These anomalous patterns need to be distinguished carefully from the highly abnormal types of EEG activity that continue to have important diagnostic value.

The EEG in progressive dialysis encephalopathy: the EEG in diagnosing and screening for PDE. (Part. I)

An EEG study was carried out on 50 patients undergoing chronic dialysis, 5 of whom had progressive dialysis encephalopathy (PDE), with the aim of confirming the reliability of EEG for diagnosing PDE and detecting patients at risk reported in previous papers. The outcome of the study confirms the high sensitivity of EEG for these purposes.

EEG findings in tick-borne encephalitis

EEG findings of epidemiologically and serologically confirmed tick-borne encephalitis patients were compared with findings of patients having acute encephalitis of viral or undetermined origins. Tick-borne encephalitis patients had more bilaterally synchronous bursts of slow waves and more focal abnormalities than did controls. Moreover, their EEGs remained mildly pathological, with increased slow and beta activity and intermittent focal abnormalities in some patients, whereas, EEGs in the controls became normal or borderline, usually within two months. EEG can thus reveal differences between individuals' responses to encephalitis and between different types of encephalitis, even though the clinical pictures are rather similar. Finally, the study shows that tick-borne encephalitis causes changes in the EEG that persist long after the clinical disease appears to have resolved.

Periodic EEG patterns in cerebral fat embolism

A 24-year-old male developed fat embolism syndrome (FES) 18 hours after accidental tibial and metatarsal fractures. The onset was characterized by coma, generalized seizures, respiratory distress and hypoxemia. Multiple prolonged portable electroencephalographic (EEG) recordings showed a variety of progressively changing patterns including continuous high amplitude EEG rhythmical synchronous slowing (CHERSS), triphasic waves, bilateral independent periodic lateralized epileptiform discharges (BIPLEDs), frontal intermittent delta activity (FIRDA), and low amplitude irregular generalized theta. Three months after the accident, the patient was neurologically normal and his EEG exhibited only rare brief bursts of anterior theta in the waking recording. I conclude that EEG periodic activity such as CHERSS, triphasic waves, BIPLEDs, and FIRDA can occur in patients suffering from cerebral fat embolism. It reflects a non-specific diffuse encephalopathy not necessarily associated with a poor prognosis. Prolonged and frequent bedside EEG recordings will demonstrate better these fluctuating abnormalities in cerebral fat embolism (and probably in coma of other origin) than standard less frequent recordings. Very likely, these periodic EEG patterns have not been previously identified in cerebral fat embolism because they were not in vogue among electroencephalographers nor widely accepted at the time studies dealing with this syndrome were written.

Neuroradiological correlates of frontally predominant intermittent rhythmic delta activity (FIRDA)

A correlative, retrospective review of 80 consecutive cases of EEG FIRDA was performed with regard to the neuroradiological findings: 62 of the 80 patients had had CAT scan evaluations. Of the 61 patients with structural pathology, 53 had CAT scans which were abnormal in 40 (76%); of the 19 patients with 'non-structural' (mostly metabolic) brain lesions, 10 had normal CAT scans. In the structural group with normal CAT scans, the presence of pathology was demonstrated by arteriography (5 cases), radionuclide cysternography (1 case), brain scan (1 case), or pathological examination. Patients with 'non-structural' FIRDA had a significantly higher probability of being in an altered state of consciousness and of having abnormal background activity in their EEG. Focal EEG abnormalities are more frequently associated with structural lesions and FIRDA. If FIRDA is present on the EEG, further neuroradiological studies should be considered, especially with other electroclinical information suggests a non-metabolic substrate.