Neonatal Seizures

Neonatal Seizures

John Giang, MD

Why it matters

Recognizing seizures on EEG is essential in neonates. Many are clinically silent, and many clinical events turn out not to be seizures. Conventional neonatal EEG is the gold standard for diagnosing and confirming neonatal seizures and status epilepticus (St. Louis & Frey, AES EEG atlas). The core skill is spotting a sudden rhythmic pattern that clearly evolves, then describing where it starts, how it spreads, and how much of the recording it takes up.

Key points

• Clinical categories:
  • Clinical-only: the clinical event has no EEG correlate.
  • Electroclinical: definite clinical signs occur together with an EEG seizure.
  • Electrographic-only: a definite EEG seizure with no visible signs.
  • Many seizures are clinically silent, so EEG may be the only way to detect them. Signs can be as subtle as a desaturation.
• ACNS definition of an electrographic seizure:
  • A sudden, repetitive pattern that evolves, reaches at least 2 µV, and lasts at least 10 s.
  • There is no minimum frequency.
  • Voltage often rises as the seizure goes on, sometimes to 150 µV or more.
  • Two events count as separate seizures only if at least 10 s separates them.
• Evolution is required. It means a clear change in frequency, voltage, morphology, or location. Evolving activity under 10 s is a brief rhythmic discharge (BRD). Rhythmic activity over 10 s that does not evolve is a rhythmic or periodic pattern, not a seizure.

• Location and spread:
  • Describe the onset site and the maximum spread.
  • Focal seizures can be frontal, central, temporal, occipital, vertex, or quadrant-based.
  • Lateralized seizures stay within one hemisphere.
  • Migrating seizures move from one hemisphere to the other.
  • Bilateral independent seizures run in two regions at the same time, each evolving on its own.
  • Diffuse seizures involve all electrodes, but asynchronously. True generalized, synchronous seizures are rare in neonates.
• Unifocal vs. multifocal onset: unifocal onset means repeated seizures from one region, which suggests a focal lesion such as stroke. Multifocal onset means at least 3 independent foci with at least one in each hemisphere, which suggests a diffuse insult such as meningitis. Focal and multifocal seizures are more common than generalized ones in neonates.
• Burden and status epilepticus:
  • Report burden as seizures per hour or as the percent of the recording in seizure.
  • Status epilepticus means seizures add up to at least 50% of any 1-hour epoch.
  • The median neonatal seizure lasts about 1 minute, and 75% last 2.5 minutes or less.

Common pitfalls

• Screening for amplitude alone. Neonatal seizures can be low amplitude or made of long-duration sharp waves, and the rhythmicity is often easier to see than the voltage.
• Calling a rhythmic pattern that does not evolve a seizure, or calling a BRD under 10 s a seizure.
• Mistaking artifact for a seizure, such as patting, suctioning, ventilator, or hypoglossal (sucking) artifact. Check that the timing does not match the artifact and that the morphology is truly spike-wave.
• Mistaking changes from arousal or drowsiness for a seizure.

Example tracing set

• Focal onset: a neonatal seizure starting in the right hemisphere and evolving in frequency and field.

• Contrast: a rhythmic occipital spike-wave run of about 4 s. It is a BRD by duration, not a seizure.