How are epileptiform normal variants differentiated from epileptiform discharges?

Updated: May 11, 2018
  • Author: Selim R Benbadis, MD; Chief Editor: Helmi L Lutsep, MD  more...
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As a whole, these normal variants must be differentiated from epileptiform discharges (see Generalized EEG Waveform Abnormalities). In general, the benign patterns lack the characteristics of pathologic epileptiform discharges—that is, the high amplitude and aftergoing slow wave or suppression that make epileptiform discharges “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.

Small sharp spikes (SSSs) are generally easy to distinguish from spikes because of their short duration and small amplitude.

Wicket spikes commonly are misinterpreted as sharp waves, especially when they occur as single sharp transients. Examining the context and determining whether they arise out of an ongoing rhythm are important. Wickets predominate in adults older than 30 years and have an incidence of 0.9%. [10]

The 14- and 6-Hz positive spikes may be distinguished from temporal spikes by their characteristic polarity (epileptiform spikes are almost always surface negative in polarity) and typical frequency. [17]

The 6-Hz phantom spike-waves may be difficult to distinguish from the definitive clinically significant spike-wave complexes. A helpful distinguishing feature is the tendency of benign 6-Hz phantom spike-waves (6 Hz) to disappear during sleep; epileptiform discharges (spike-wave complexes) tend to persist or become more prominent with deeper levels of sleep. [18, 19, 20]

Psychomotor variant (rhythmic midtemporal theta of drowsiness [RMTD]) differs from a seizure discharge in that it is usually a monomorphic or monorhythmic pattern that does not evolve into other frequencies or waveforms, as usually occurs during seizures.

The subclinical rhythmic electroencephalographic (EEG) discharges of adults (SREDA) pattern is never associated with symptoms, in contrast to a seizure pattern. [21]

Midline theta (Ciganek) rhythm does not have any clinical significance. Like many other patterns, 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. [22, 23]

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