Neonatal Epileptiform Discharges

Neonatal Epileptiform Discharges

John Giang, MD

Why it matters

Sharp activity shows up in many healthy newborns, so the main job is separating normal sharp transients from pathologic ones. ACNS admits the dividing line is still debated. It sorts sharp transients by polarity, duration, abundance, spatial distribution, and repetition. No single feature decides it. Read every discharge alongside the background and the infant's postmenstrual age (PMA).

Key points

• Definitions:
  • Spike: lasts under 100 ms.
  • Sharp wave: lasts 100–200 ms.
  • Either one must stand clearly apart from the background, not just be "sharply contoured background activity".
• Physiologic negative sharp waves:
  • Occur on a normal background.
  • Mostly midtemporal, central, or centrotemporal; rare at frontal, vertex, and occipital sites.
  • Symmetric between hemispheres.
  • Usually single events.
• Abnormal negative sharp waves:
  • Usually occur on a background that is abnormal for PMA.
  • Clustered in one region or one hemisphere, or found at atypical sites (frontal, vertex, occipital).

• • More abundant, and more likely to come in runs or trains.
• Abundance threshold: more than 11 per hour is abnormal in preterm infants and more than 13 per hour in term infants. Count them in wakefulness or active sleep, not in tracé alternant, where bursts naturally contain sharply contoured activity.
• Positive sharp waves: positive rolandic and positive vertex sharp waves mark white-matter injury, including periventricular leukomalacia (PVL). At term, excessive positive midtemporal sharps can signal a focal hemorrhage or white-matter injury. They reflect structural injury rather than seizure risk.
• Features that raise concern:
  • Negative polarity.
  • Spike-and-slow-wave morphology.
  • A true field that disturbs the background.
  • Midline or occipital location.
  • Persistent focality, rhythmicity, or asymmetry.
  • Spikes during wakefulness or active sleep after about 42 weeks PMA.
• Brief rhythmic discharges (BRDs):
  • Evolving rhythmic activity lasting under 10 s.
  • Usually seen with an abnormal background or confirmed seizures.
  • Rarely seen in a normal EEG.
  • One case series linked them to outcomes similar to seizures.
• Boundary with seizures:
  • An electrographic seizure is a repetitive pattern that evolves, reaches at least 2 µV, and lasts at least 10 s.
  • Rhythmic activity over 10 s that does not evolve is called periodic or rhythmic activity, not a seizure.
  • Status epilepticus means seizures fill at least 50% of a 1-hour epoch (ACNS).

Common pitfalls

• At the neonatal display speed of 15 mm/s the tracing looks compressed, so ordinary activity can appear sharper than it is.
• Counting sharp activity embedded in tracé alternant bursts as discharges.
• Overcalling rare scattered temporal sharps in healthy term infants.
• Mistaking single-electrode artifact for a sharp wave.
• Status epilepticus ACNS definition in neonate is different than infant or adult criteria, which is at least 20% of a 1-hour epoch.
• Missing low-amplitude seizures, which may be clinically silent.