Normal variants and artifacts: Importance in EEG interpretation

Abstract

Overinterpretation of EEG is an important contributor to the misdiagnosis of epilepsy. For the EEG to have a high diagnostic value and high specificity, it is critical to recognize waveforms that can be mistaken for abnormal patterns. This article describes artifacts, normal rhythms, and normal patterns that are prone to being misinterpreted as abnormal. Artifacts are potentials generated outside the brain. They are divided into physiologic and extraphysiologic. Physiologic artifacts arise from the body and include EMG, eyes, various movements, EKG, pulse, and sweat. Some physiologic artifacts can be useful for interpretation such as EMG and eye movements. Extraphysiologic artifacts arise from outside the body, and in turn can be divided into the environments (electrodes, equipment, and cellphones) and devices within the body (pacemakers and neurostimulators). Normal rhythms can be divided into awake patterns (alpha rhythm and its variants, mu rhythm, lambda waves, posterior slow waves of youth, HV‐induced slowing, photic driving, and photomyogenic response) and sleep patterns (POSTS, vertex waves, spindles, K complexes, sleep‐related hypersynchrony, and frontal arousal rhythm). Breach can affect both awake and sleep rhythms. Normal variants or variants of uncertain clinical significance include variants that may have been considered abnormal in the early days of EEG but are now considered normal. These include wicket spikes and wicket rhythms (the most common normal pattern overread as epileptiform), small sharp spikes (aka benign epileptiform transients of sleep), rhythmic midtemporal theta of drowsiness (aka psychomotor variant), Cigánek rhythm (aka midline theta), 6 Hz phantom spike–wave, 14 and 6 Hz positive spikes, subclinical rhythmic epileptiform discharges of adults (SREDA), slow‐fused transients, occipital spikes of blindness, and temporal slowing of the elderly. Correctly identifying artifacts and normal patterns can help avoid overinterpretation and misdiagnosis. This is an educational review paper addressing a learning objective of the International League Against Epilepsy (ILAE) curriculum.

The effects of slow wave sleep characteristics on semantic, episodic, and procedural memory in people with epilepsy

“…In the future, automated sleep scoring will most likely replace the time-consuming task of sleep staging ( Fiorillo et al, 2019 ). However, automated sleep scoring might not be accurate in epilepsy, as epileptiform activity can represent confounders for algorithms that have been developed for sleep staging in healthy individuals ( Amin et al, 2023 ). The present approach is therefore preferable given the current state of the art of sleep staging.…”

Interictal epileptiform discharges in Alzheimer’s disease: prevalence, relevance, and controversies

“…An interictal epileptiform abnormality should be defined by at least 4 out of 6 criteria recommended by the international federation for clinical neurophysiology to avoid misinterpretation of normal variants on EEG ( 19 ). Common normal variants in older adults that can be easily misinterpreted as pathologic include small sharp spikes, wicket rhythms, and wicket spikes ( 8 ). Yet, even when these criteria are applied, there may be substantial interrater variability; the inter-rater reliability regarding IEDs is fair at best even among experts ( 21 ).…”

“…Electroencephalography (EEG) has proven to be the most accessible and cost-efficient tool to identify epileptiform abnormalities in patients with mild cognitive impairment (MCI) or Alzheimer’s dementia ( 4 , 5 ). Albeit there may be substantial variability in the interpretation and reporting of the data ( 8 ). There is a need for clinicians to understand the EEG findings in patients with AD, its role in the pathogenesis and progression of the disease, and when and whether certain findings should be treated.…”

Explainable classification of seizures and other patterns of harmful brain activity in critically ill patients

“…Seizures are serious threats to the neurological well-being and are associated with long term cognitive de cits if missed or mistaken [3]. Other patterns of abnormal brain activity including periodic discharges and rhythmic activities are associated with underlying neurological injuries and must be studied for interpretation [4]. Classi cation of seizures and other abnormal brain activities in the critically ill patients is challenging and multi-factorial process that considers integrated analysis of clinical symptoms, EEG ndings and neuroimaging studies [5].…”