Spikes and sharp waves

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  • 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%. [1]
  • After a first seizure, the presence of interictal spikes and sharp waves doubles the likelihood of seizure recurrence. [2]
  • The absence of interictal spikes and sharp waves does not prove that the patient does not have epilepsy.

Do not confuse with:


  1. 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.
  2. Berg AT, Shinnar S. risk of seizure recurrence following a first unprovoked seizure: a quantitative review. Neurology. 1991. 41:965-72.