Spikes and sharp waves

• Sharply contoured transients, clearly distinguishable from and usually interrupt background activities
• Almost always negative wave, so pointed upwards on the EEG
• Spike: Duration of <70 milliseconds
• Sharp wave: Duration of 70-200 milliseconds
• No difference in etiology or prognosis between a spike or sharp wave

Clinical relevance

• If seen in a patient with reasonably high suspicion of a seizure, the predictive value of spikes and sharp waves for epilepsy is high .
• In healthy adults, spikes and sharp waves are seen in about 0.5-1%. In healthy children in about 3-5%.
• After a first seizure, the presence of interictal spikes and sharp waves doubles the likelihood of seizure recurrence.
• The absence of interictal spikes and sharp waves does not prove that the patient does not have epilepsy.

Do not confuse with:

• Small sharp spikes (SSS or BETS)
• Wicket spikes
• 6 Hz spike-and-wave bursts (WHAM and FOLD)
• ECG artifact
• Muscle artifact
• Eye blink artifact