What Does “Subclinical Rhythmic Electrographic Discharge of Adults” in EEG Signify?

Four Atypical Cases of Subclinical Rhythmic Electroencephalogram Discharge of Adults: Case Series and Review

SUMMARY

Subclinical rhythmic EEG discharge of adults is an uncommon variant that represents a diagnostic challenge in the clinical practice because it can be mistaken for an electrographic seizure. We present a case series of four patients who underwent EEG because of suspicious events or an unclear medical history of epilepsy. In all cases, the EEG revealed atypical features including focal and asymmetric distribution, presentation during NREM and REM sleep, rhythmic activity in the delta range with a notched appearance and blocked by eyes opening.

Pitfalls in scalp EEG: Current obstacles and future directions

Although electroencephalography (EEG) serves a critical role in the evaluation and management of seizure disorders, it is commonly misinterpreted, resulting in avoidable medical, social, and financial burdens to patients and health care systems. Overinterpretation of sharply contoured transient waveforms as being representative of interictal epileptiform abnormalities lies at the core of this problem. However, the magnitude of these errors is amplified by the high prevalence of paroxysmal events exhibited in clinical practice that compel investigation with EEG. Neurology training programs, which vary considerably both in the degree of exposure to EEG and the composition of EEG didactics, have not effectively addressed this widespread issue. Implementation of competency-based curricula in lieu of traditional educational approaches may enhance proficiency in EEG interpretation amongst general neurologists in the absence of formal subspecialty training. Efforts in this regard have led to the development of a systematic, high-fidelity approach to the interpretation of epileptiform discharges that is readily employable across medical centers. Additionally, machine learning techniques hold promise for accelerating accurate and reliable EEG interpretation, particularly in settings where subspecialty interpretive EEG services are not readily available. This review highlights common diagnostic errors in EEG interpretation, limitations in current educational paradigms, and initiatives aimed at resolving these challenges.

SREDA: An Uncommon and Misleading EEG Rhythm

Subclinical Rhythmic Electroencephalographic Discharges of Adults (SREDA) is a benign EEG variant characterized by sharply contoured rhythmic theta activity occurring bilaterally with maximum activity over the parietal or the posterior head region. These paroxysms are not associated with any objective or subjective clinical manifestations. SREDA, the rarest and last reported benign EEG pattern with no known clinical significance yet, is detailed in this case report. We provide the case of a gentleman with epilepsy who underwent vEEG recording in our lab. The described case is interesting due to its EEG characteristics as well as its clinical picture, which misled us for at least a while. It provides an illustration of how over interpretation of normal EEG patterns may result in an incorrect diagnosis.

Critically ill benign EEG variants: Is there such a thing?

Despite growing use of critical care electroencephalography (ccEEG) to detect seizures and status epilepticus in the intensive care unit (ICU), integrating ccEEG findings with traditionally described benign EEG variants (BEVs) is a relatively new concept. BEV-like waveforms are now increasingly encountered in the ICU, and have also been explicitly included in proposed definitions of brief potentially ictal rhythmic discharges (BIRDs) in the ICU, bringing to the fore the question of if and which EEG patterns in critically ill patients can be safely deemed "benign". Though well-characterized as benign in healthy outpatients at low pre-test risk for neurologic disease, the significance of BEVs in the ICU remains largely unknown. Simultaneously, there has been mounting evidence to suggest that certain BEVs can arise from heterogeneous intracranial sources, including some pathologic generators. We conducted an extensive literature review on all known BEVs to assess what is known of BEVs in the ICU. Here we discuss critically ill BEVs and how to interpret them.

SREDA: A Rare but Confusing Benign EEG Variant

INTRODUCTION

Subclinical rhythmic EEG discharges in adults (SREDA) is a very rare benign EEG pattern. The electrophysiological features and atypical variants of SREDA has wide spectrum and they are poorly known. It resembles ictal discharges, and overinterpretation of SREDA may lead to misdiagnosis of epilepsy. Herein, we aimed to report patients with SREDA to identify the frequency and characterized clinical, demographic, electrophysiological features.

METHODS

We reviewed 22,234 EEG reports that are reported by the same experienced clinical neurophysiologists, between 2012 and 2018. The EEGs with SREDA were reevaluated blindly by three clinical neurophysiologists. The demographic, clinical characteristics, and neuroimaging features of the patients were reviewed.

RESULTS

Subclinical rhythmic EEG discharges in adults was present in 14 EEG records (0.06%), in nine patients. The mean age of patients was 52.1 ± 17.7 (range, 21-71) years. The patients had been diagnosed with several neurologic diseases, including cerebrovascular disease, epilepsy, psychogenic nonepileptic seizures, mental retardation, Alzheimer disease, and transient global amnesia. One patient had unilateral lesion, in whom SREDA had appeared on contralateral side of the lesion, whereas other patients with normal or nonlateralized lesions had SREDA bilaterally and symmetrical. This variant had been misdiagnosed as an ictal discharge in previous EEGs in three patients.

CONCLUSIONS

This study indicates that SREDA is difficult to associate with any specific condition. The pathophysiology of SREDA can not be explained by a single mechanism. Even if it is mostly observed in older adults, it is also observed in young adults in this study. It is important to differentiate SREDA from ictal discharge to prevent misdiagnosis of epilepsy especially in nonepileptic paroxysmal events.

Atypical SREDA During Wakefulness, NREM and REM Sleep in a Young Teenager: A Diagnostic Challenge

Subclinical rhythmic electrographic discharges of adult (SREDA) is a rare variant considered to be normal in EEG. It consists of sharp-contoured or sinusoidal waveforms in the theta frequency range (usually 5-7 Hz), occurring in a widespread distribution, often maximal over the parietotemporal regions. SREDA is usually bilateral but could be unilateral (atypical SREDA). Compared with true ictal activities, SREDA has little change in frequency, morphology, and distribution. It has been described in adults and is extremely rare in children/adolescents. There are only 5 cases published in children. We report a case of atypical SREDA in a child that may have occurred in wakefulness, non-rapid eye movement (NREM) sleep, and REM sleep. This finding was initially misdiagnosed as epilepsy. Inpatient video-EEG demonstrated that during periods of SREDA in quiet wakefulness the patient did not have any signs or symptoms with the SREDA pattern; SREDA abated whenever the patient was alerted or if he spontaneously initiated some activities. SREDA with same morphology was noted in NREM and REM sleep. The patient had no true epileptogenic abnormalities and hence antiepileptic medication was discontinued and stopped uneventfully. This case illustrates the importance of recognizing this rare variant, avoiding a misdiagnosis of epilepsy as it occurred in our case.

Prevalence of benign epileptiform variants during initial EEG examination in French military aircrew

INTRODUCTION

In France, a systematic EEG is performed during initial examination in military aircrew applicants, which may provide an estimation of the prevalence of benign epileptiform variants in healthy adults.

METHODS

We analyzed standard EEG (21 scalp electrodes, 20minutes, 400Hz sampling rate) of military aircrew applicants examined in the French Main Aeromedical Center in 2016. EEGs were analyzed using both bipolar and referential montages. The collected data were EEG abnormalities and benign epileptiform variants. The kappa inter-observer index for the detection of benign epileptiform variants was calculated.

RESULTS

Our population was composed of 495 subjects (86.7% males, mean age 22.5±4.8 years), wishing to become a pilot in 69.7% of cases. None of the applicants reported any neurological disease and none was taking regular medication. EEG was considered as normal for 96.4% of them. Encountered EEG abnormalities were mainly asymmetric and sharp slow wave bursts. Drowsiness was recorded during 13.9% of these EEG. Benign epileptiform variants were present in 7.7% of our population: anterior theta activities (4%), posterior slow waves (2.8%), alpha variants (0.6%) and wicket spikes (0.2%). Hyperventilation induced EEG slowing in 14.1% of cases. During intermittent photic stimulation, physiological photic driving was observed in 15.2% of subjects.

DISCUSSION

Many previous studies have been dedicated to the prevalence of benign epileptiform variants but results are often heterogeneous and based on patients in whom there was an indication for EEG. Our results thus bring data on benign epileptiform variants prevalence in a young adult population characterized by the absence of neurologic disorders. Our study demonstrates that anterior theta activities, posterior slow waves, alpha variants and wicket spikes are the most frequent benign EEG variants in such a young adult population.