West Syndrome (Infantile Spasm)

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West syndrome


  • Severe epilepsy syndrome with the triad:
    • Infantile spasm
    • Hypsarrhythmia
    • Mental retardation
  • Onset: 90% in the first 12 months after birth, with a peak onset between 4 and 6 months
  • Incedence: 3 to 5/10,000 live births
  • 2% of childhood epilepsies
  • Classified according to etiology (old International League Against Epilepsy (ILAE) classification)
    • Symptomatic (almost any disorder than can cause brain damage) ie:
      • Trisomy 21 (Down syndrome)
      • Trauma
      • Infectious (meningitis, encephalitis)
      • Metabolic disorders (ie maple syrup urine disease, mitochondrial encephalopathy, pyridoxine dependency)
      • Hydrocephalus/microcephaly
      • Tuberous sclerosis
      • Ischemic encephalopathy
    • Cryptogenic
      • If a symptomatic cause is most probable, however the cause is not identified.
      • 8-42% of the West syndromes
    • Idiopathic
      • 9-14% of the West syndromes
      • In contrast to cryptogenic West, there is a normal development until the onset.
      • No MRI abnormalities
  • New International League Against Epilepsy (ILAE) classification:
    • Genetic
    • Structural/metabolic
    • Unknown


  • Psychomotor arrest or regression
  • Spasms, sudden contraction of the trunk en limb lasting around 2 - 10 seconds
    • Flexor spasm (Salaam spasm): Rapid bending of the head and torso forward and simultaneous raising and bending of the arms, similar to the greeting between muslims (Salaam)
    • Extensor spasm: Extension of the neck and trunk and with extension and abduction of the limbs
    • Mixed spasm
  • 1 to 30 clusters/day of 20 to 100 spasms each cluster



  • Hypsarrhythmia: high voltage, chaotic, slow waves and spikes in all cortical areas. The spikes originate from multiple foci and have no rhythmical or repetitive organization.
  • The typical hypsarrhythmia is usually seen in the early stage of West syndrome
  • The EEG gradually evolves to a more synchronized, with increased hemispheric synchronization en symmetry.
  • Hypsarrhytmia is most pronounced in sleep and the patients have reduces or absent non-REM sleep.
  • Other interictal patterns: diffused (encephalopathic) or focal slowing, multifocal Spike slow wave complex
  • The EEG can evolve towards a EEG seen in Lennox Gastaut Syndrome

Ictal EEG

  • High-voltage, frontal dominant, generalized slow-wave transient followed by voltage attenuation

West syndrome with hypsarrhytmia (multifocal spike and slow waves, with little organization) in a 8 months old girl (average)

West syndrome with hypsarrhytmia in a 8 months old girl (average) EEGpedia.png