West's syndrome

Last reviewed 05/2021

Infantile spasm (IS), also known as West syndrome, is a unique form of epilepsy present almost entirely during infancy (the first year of life) (1). IS was first described in 1841 by Dr. William James West in a letter to Lancet, describing new infantile convulsions in his 4-month-old son (2).

The condition is characterised by the triad of:

  • clinical flexor or extensor spasms, often involving the extremities and head/neck
  • hypsarrhythmia on electroencephalogram (EEG)
  • subsequent or concurrent intellectual disability (2)

IS is seen in roughly 2-3 per 10,000 live births

  • it is commonly seen between 3 and 8 months of age with a peak incidence at 6 months of age
    • only <10% of cases present in infants older than 1 year of age
    • onset up to 4 years of age has also been reported
  • spasms usually cease by 5 years of age. However other seizure types may occur in as many as 60% even after cessation of IS 
  • all ethnic groups are affected, boys are affected slightly more often than girls (ratio of 60:40) (2,3)
  • a family history can be identified in 3%–6% of cases (4)

IS can be classified aetiologically into 3 categories:

  • cryptogenic form
    • underlying cause cannot be identified
    • prior developmental delays
    • normal neurological exam and neuroimaging, and no abnormality in the metabolic evaluation
    • outcomes are more favourable than in symptomatic category
    • early effective treatment will result in improved prognosis
  • symptomatic form
    • underlying structural, metabolic or genetic cause can be identified
    • developmental delay is seen prior to the onset of spasms
  • idiopathic
    • normal development prior to onset of spasms
    • no residual dysfunction
    • normal neuroimaging and normal etiologic evaluation, and normal neurodevelopment.