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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%.
- 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
- 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
- Genetic and neurocutaneous conditions noted above