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
- 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
- Okubo et al, Epileptiform EEG discharges in healthy children: prevalence, emotional and behavioral correlates, and genetic influences, Epilepsia. 1994 Jul-Aug;35(4):832-41.
- Berg AT, Shinnar S. risk of seizure recurrence following a first unprovoked seizure: a quantitative review. Neurology. 1991. 41:965-72.