infantile spasms

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.

Reference:

• (1) Taghdiri MM, Nemati H. Infantile spasm: a review article. Iran J Child Neurol. 2014;8(3):1-5. 
• (2) Nelson GR. Management of infantile spasms. Transl Pediatr. 2015;4(4):260-70. 
• (3) Wheless JW et al. Infantile spasms (West syndrome): update and resources for pediatricians and providers to share with parents. BMC Pediatr. 2012;12:108
• (4) Go CY et al. Evidence-based guideline update: medical treatment of infantile spasms. Report of the Guideline Development Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society. Neurology. 2012;78(24):1974-80.