Infantile Spasms is a topic covered in the Select 5-Minute Pediatrics Topics.

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  • An epileptic encephalopathy of infancy or early childhood consisting of myoclonic seizures and electroencephalographic pattern: High-voltage slowing, asynchrony, disorganization, and multifocal spikes (hypsarrhythmia)
  • Seizures can be flexor, extensor, mixed flexor/extensor, or arrest/akinetic. They occur in clusters, typically upon awakening or drowsiness, and can have focal features.
  • The combination of infantile spasms, hypsarrhythmia, and developmental arrest is known as West syndrome.
  • Infantile spasms (ISs) are symptomatic if the child has a coexistent neurologic condition or developmental delay at presentation, or if a specific etiology can be identified. They are cryptogenic if no underlying cause is found.


90% have onset <1 year of age, with the majority between 3 and 7 months. Onset after 18 months is rare.


Incidence is 0.16–0.42/10,000 live births. In patients with tuberous sclerosis complex the incidence is 68%.

Risk Factors


  • Most cases are sporadic with a positive family history of IS present in 3–6%.
  • Tuberous sclerosis complex may be sporadic or autosomal dominant.
  • X-linked infantile spasm syndromes (ARX, CDKL-5), and chromosomal ( STXBP-1) show variable penetrance.


  • Genetic syndromes:
    • Neurocutaneous disorders: Tuberous sclerosis complex, incontinentia pigmenti, neurofibromatosis type I (NF1)
    • Down syndrome
    • X-linked infantile spasm syndromes: ARX, CDKL5, Aicardi syndrome
    • Autosomal infantile spasm syndromes: Miller-Dieker syndrome (17p13.3), 18q and 7q duplication, partial 2p trisomy, and STXBP1 and MAGI2 deletions
  • Metabolic disorders:
    • Congenital lactic acidoses and mitochondrial disorders
    • Phenylketonuria
    • Nonketotic hyperglycinemia
    • Pyridoxine and folinic acid deficiency syndromes
  • Malformations of cortical development
  • Almost any cause of prenatal, perinatal, or early infantile brain injury may lead to infantile spasms, including meningitis, encephalitis, hypoxic-ischemic injury, abusive head trauma, stroke, and congenital infection.
  • ∼40% of infantile spasms are cryptogenic, but that percentage may decrease with recent genetic discoveries.

Commonly Associated Conditions

  • Intrauterine infection, CNS infections
  • Cerebral malformations: Malformation of cortical development
  • Hypoxic-ischemic encephalopathy, perinatal asphyxia, prenatal/perinatal stroke
  • Abusive head trauma
  • Intraventricular hemorrhage
  • Kernicterus
  • Genetic and neurocutaneous conditions noted above

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