How are sporadic focal interictal epileptiform discharges (IEDs) characterized on EEG?

Updated: Oct 09, 2019
  • Author: Alexis D Boro, MD; Chief Editor: Selim R Benbadis, MD  more...
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Sporadic IEDs are categorized as spikes or sharpwaves. By convention, a spike is defined as an IED of less than 70 milliseconds in duration and a sharp wave as an IED of 70-200 milliseconds in duration. The distinction between these 2 patterns has no etiologic or prognostic significance. In clinical discussions the terms are often used interchangeably.

In a patient in whom there is some doubt as to whether a paroxysmal event represented an epileptic seizure, the presence of spikes or sharp waves on a routine EEG often resolves the question. Because spikes and sharp waves occur rarely in the general population—the incidence is about 1% in healthy adults and 3% in healthy children and somewhat higher in hospitalized patients—when an EEG is performed in a patient in whom there is reasonably high suspicion that the patient had a seizure, the predictive value of IEDs is high. The presence of IEDs in a routine EEG also can yield significant prognostic information that can be important when making decisions about instituting antiepileptic therapy. In patients examined after a first seizure, the presence of IEDs is associated with an approximately 2-fold increased likelihood of seizure recurrence. [7] Generalized epileptiform discharges tend to be more predictive of seizure recurrence than focal IEDs.

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