You are in: eMedicine Specialties > Neurology > Electroencephalography Atlas EEG Atlas: Epileptiform Normal VariantsArticle Last Updated: Sep 27, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 6
  Author: Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital Selim R Benbadis is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association Coauthor(s): Diego Rielo, MD, Staff Physician, Department of Neurology, Memorial Hospital West, Memorial Hospital Pembroke, Memorial Healthcare Editors: Leslie Huszar, MD, Consulting Staff, Department of Neurology, Indian River Memorial Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital; Paul E Barkhaus, MD, Professor, Department of Neurology, Medical College of Wisconsin; Director of Neuromuscular Diseases, Milwaukee Veterans Administration Medical Center; Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants Author and Editor Disclosure Synonyms and related keywords: EEG atlas, epileptiform normal variants, benign epileptiform transients of sleep, midline theta, phantom spikes and waves, psychomotor variants, small sharp spikes, SSS, subclinical rhythmic EEG discharges of adults, SREDA, wicket spikes, 14- and 6-Hz positive spikes INTRODUCTIONSection 2 of 6
  Epileptiform normal variants are EEG patterns that resemble epileptogenic abnormalities. Most of these patterns initially were thought to be associated with epilepsy or other neurological conditions but subsequently were demonstrated to have no such significance. They now are considered normal variants of no clinical significance. Their recognition is important to avoid overinterpretation or misinterpretation with regard to their significance. This article reviews the following such patterns: small sharp spikes (SSS), wicket spikes, 14- and 6-Hz positive spikes, phantom spike and waves, psychomotor variants, subclinical rhythmic EEG discharges of adults (SREDA), and midline theta. Most of these patterns initially were described in the 1950s. Gibbs and Gibbs described small sharp spikes in 1952, and 14- and 6-Hz positive spikes were described at approximately the same time (Gibbs, 1951; Grossman, 1954; Kellaway, 1959; Nidermeyer, 1961). The 6-Hz phantom spike-wave was described by Walter (1950), and the psychomotor variant was described by Gibbs and Gibbs (1952). Wickets were described in 1977 (Reiher and Lebel). WAVEFORM DESCRIPTIONSSection 3 of 6
Small sharp spikes (Images 1-3): Also known as benign epileptiform transients of sleep (BETS), SSSs occur in light sleep (stages I and II of nonrapid eye movement [NREM] sleep), usually sporadically. Location is temporal, either unilateral or bilaterally independent, and with a broad field of distribution. Morphology is typically monophasic, occasionally diphasic, and the decline after the first negative peak is very steep. SSSs rarely may have a single aftergoing slow-wave component but generally are not disturbing the background. The main features of SSSs are in their name: duration is short, amplitude is small, and an easy guideline states that SSSs generally should be less than 50 mV and less than 50 milliseconds. Wicket spikes (Images 4-6): Wicket spikes occur in both awake state and light sleep. Frequency is 6-11 Hz, usually in short runs (wicket rhythm) but also as single sharp transients. Location is temporal, usually bilateral and independent. Morphology is archlike or mu-like, sharp, monophasic, and not followed by an aftergoing slow wave. Amplitude may be high, but the transient arises out of an ongoing rhythm and does not stand out. The 14- and 6-Hz positive spikes: This pattern is observed at any age, but it is expressed maximally in adolescents, especially those aged 13-14 years (Klass and Westmoreland, 1985). The 6-Hz positive spikes predominate in children younger than 1 year and in adults older than 40 years, and the 14-Hz positive spikes predominate or combine with 6-Hz spikes in the other age groups (Gibbs et al, 1963). Both 14- and 6-Hz positive spikes are observed predominantly during light sleep. These spikes usually appear in short runs lasting less than 2 seconds, and their frequencies, as the name implies, are 14 Hz and 6 Hz. Location is mostly posterior temporal, unilaterally or bilaterally. Morphology is a sharply contoured positive spike alternating with rounded negative component. Amplitude is medium, around 20-60 µV. Phantom spike and wave (6 Hz): The 6-Hz spike and wave pattern may be observed in both adolescents and adults. It generally occurs during relaxed wakefulness and stage I sleep and disappears during deeper levels of sleep. Frequency is 6 Hz, and the bursts last 1-2 seconds. Location is usually diffuse, bisynchronous, and relatively symmetric. This pattern may predominate in the anterior and posterior head regions. Morphology is a typically small ( <30 µV and <30 ms), evanescent diphasic spike followed by a higher (50-100 µV) slow wave component. Thus, the spike component may be difficult to see. Psychomotor variant (Image 7): A more useful and descriptive term is rhythmic midtemporal theta of drowsiness (RMTD). Frequency is theta (4-7 Hz). Location is maximum midtemporal, unilateral or bilaterally independent or bisynchronous. Morphology typically is notched, flat topped, or sharply contoured. Bursts may last 1-10 seconds or longer and thus resemble temporal lobe seizures. Amplitude is medium to high. Subclinical rhythmic EEG discharges of adults: SREDA is an uncommon pattern observed mainly in older persons (>50 y). It may occur at rest or during drowsiness. SREDA superficially resembles an EEG seizure pattern. Frequency is typically 5-6 Hz. Location is widespread or bilateral with a posterior maximum. Morphology is seizurelike (ie, rhythmic sharply contoured theta). Abrupt onset and termination may help distinguish SREDA from an EEG seizure. Duration ranges from 20 seconds to minutes (average 40-80 s). Midline theta rhythm (ie, Ciganek rhythm): Midline theta rhythm may be observed during wakefulness or drowsiness. As indicated by the name, frequency is 4-7 Hz, and the location is midline (ie, vertex). Morphology is rhythmic, smooth, sinusoidal, arciform, spiky, or mu-like. CLINICAL CORRELATIONSection 4 of 6
As a whole, these normal variants need to be differentiated from epileptiform discharges (ie, spikes, sharp waves, spike-wave complexes; see Generalized EEG Waveform Abnormalities). In general, the benign patterns lack the characteristics of pathological epileptiform discharges, high amplitude and aftergoing slow wave or suppression, making them "disturbing" to the background activity. By default, assume that sharp transients are benign variants, and consider them epileptiform and abnormal only if they do not meet criteria for any benign transients. SSS are generally easy to distinguish from spikes because of their short duration and small amplitude. The 14- and 6-Hz positive spikes should not be confused with temporal spikes because of their characteristic polarity (epileptiform spikes are almost always surface negative in polarity) and typical frequency. Phantom spike and waves (6 Hz) may be difficult to distinguish from the definitive clinically significant spike and wave complexes. A helpful way to distinguish them is by the tendency of benign phantom spike and waves (6 Hz) to disappear during sleep; epileptiform discharges (spike and wave complexes) tend to persist or become more prominent with deeper levels of sleep. Psychomotor variant differs from a seizure discharge because it is usually a monomorphic or monorhythmic pattern that does not evolve into other frequencies or waveforms as usually occurs during seizures. Wicket spikes commonly are misinterpreted as sharp waves, especially when they occur as single sharp transients. Examining the context and whether they arise out of an ongoing rhythm is important. Wickets predominate in adults older than 30 years and have an incidence of 0.9% (Reiher, 1977). SREDA is never associated with symptoms, in contrast to a seizure pattern. Midline theta rhythm does not have any clinical significance and appears to represent a nonspecific variant of theta activity. As with many others, this pattern initially was believed to occur predominantly in patients with temporal lobe epilepsy. Later reviews have shown that the Ciganek rhythm represents a nonspecific variant of theta activity (Mokran, 1971; Westmoreland, 1986). MULTIMEDIASection 5 of 6
REFERENCESSection 6 of 6
EEG Atlas: Epileptiform Normal Variants excerpt Article Last Updated: Sep 27, 2006 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
