The IFCN criteria for epileptiform discharge (identification ≥4 of 6 criteria = epileptiform)

The slide shows the International Federation of Clinical Neurophysiology criteria for epileptiform discharge, based on identification of ≥4 of the 6 criteria:¹

1. sharp or spiky morphology (20–70 milliseconds for spike waves; 70–200 milliseconds for sharp waves)²
2. different wave duration than background activity¹
3. waveform asymmetry¹
4. after-going slow wave¹
5. disruption of background activity: flattening or low-voltage alpha or beta frequency activity after
   (most frequently) or before sharp transient¹
6. distribution suggestive of cerebral source/physiologic field.¹

(Criteria 4 and 5 are independent.)

The paroxysmal depolarizing shift (PDS) is a large-amplitude depolarization associated with action potential bursting, it represents the cellular counterpart of the interictal spike that occurs between focal seizures on an EEG.³

Six characteristic features in an EEG can be used to identify interictal epileptiform discharges.¹

EEG=electroencephalogram; IFCN=International Federation of Clinical Neurophysiology