Epileptiform Discharge
According to IFCN, a waveform can be considered epileptiform if ≥4 of 6 defining features are present:
1️⃣ Physiological field of distribution
-The discharge must have a plausible neurophysiological field.
-It should show:
>A clear phase reversal
>A logical spatial voltage gradient
>Distribution consistent with cortical generators
This helps differentiate true cortical discharges from artifact or benign variants
2️⃣ Morphology: spike or sharp wave
-The waveform must have the morphology of:
>Spike: duration < 70 ms
>Sharp wave: duration 70–200 ms
These reflect synchronous neuronal depolarization
3️⃣ Asymmetry of the waveform
-The ascending limb is steeper and more vertical
-The descending limb is slower and less steep
This asymmetry distinguishes epileptiform discharges from benign rhythmic activity
4️⃣ After-Coming Slow Wave
-A true epileptiform discharge is often followed by a slow wave
-This represents:
>Spike → depolarization
>Slow wave → inhibitory postsynaptic potentials/repolarization
The slow wave reinforces epileptogenic significance
5️⃣ Duration Different from Background
-The waveform should have a clearly different duration from surrounding background rhythms
-It should stand out from alpha, theta, or delta activity
This ensures it is not a fragment of background oscillation
6️⃣ Disruption of Background Activity
-The discharge should interrupt or distort ongoing background rhythms
-There may be:
>Transient attenuation
>Phase resetting
>Background interruption
This indicates abnormal cortical synchronization