ABSTRACT
Normal and variant EEG patterns often simulate abnormalities and their misinterpretation can lead to harmful misdiagnoses of epilepsy. Consequently, expertise in these phenomena is fundamental for patient safety. Mastery of normal features must include the Alpha rhythm, Mu rhythm, beta activity, slow activity, posterior slow waves of youth, Lambda waves, hyperventilation and photic responses, drowsy patterns, vertex waves, sleep spindles, K-complexes and positive occipital sharp transients of sleep. Features clearly outside of and unequivocally distinct from the abundantly wide range of normal are possibly abnormal. However, there are several distinctive benign variant patterns that resemble epileptiform abnormalities or seizure discharges, but which are not associated with epilepsy. Clinical diagnosis must exclude these insignificant patterns, which include small sharp spikes, 14 and 6 Hz positive bursts, 6 Hz "phantom" spike-and-wave, wicket waves, rhythmic temporal theta bursts of drowsiness, subclinical rhythmic electrographic discharges of adults, midline theta and frontal arousal rhythm. Proper normal and variant pattern recognition is precise and criteria-based rather than subjective. Because amplitude and sharpness per se are insufficient discriminators, analysis also considers frequency, distribution, morphology, polarity, state-dependence, reactivity and symmetry. This illustrated review summarizes multi-factorial criteria that identify some normal and benign variant phenomena