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- Infantile spasms (IS) are seizures commonly associated with West syndrome—a severe infantile epileptic encephalopathy often with poor developmental outcome.
- IS are characterized by sudden flexion, extension, or mixed flexion-extension of the neck, trunk, arms, and or legs.
- IS can be subtle such as a mild contraction of the abdominal muscles or subtle movements of the head, shoulder, or eyes.
- IS can occur singly, but the clustering (often on awakening) is helpful for diagnosis.
- IS are commonly dismissed as “normal” movements or misdiagnosed as reflux/colic.
- West syndrome is classically the triad of (i) IS, (ii) developmental delay, and (iii) hypsarrhythmia—a chaotic and high amplitude EEG background disrupted by frequent multifocal spikes.
- The onset occurs in the 1st year of life in >90%, typically 3 to 12 months of age (peak onset 4 to 8 months, mean 6 months).
- Spasms rarely occur after 18 months of age.
- Given that spasms can occur outside the infantile period, the preferred inclusive terminology for this seizure type is epileptic spasm.
The incidence is 2 to 3.5/10,000 live births.
- In 70–80% of cases, a specific condition is associated with IS; however, this does not necessarily suggest a direct cause-and-effect relationship with IS.
There is an expanding list of IS-associated genes: CDKL5 (more girls than boys), STXBP1, ARX (boys), ALG13, DOCK7, DNM1, FOXG1 (duplications), GABRB1, GABRB3, GNAO1, GRIN1, GRIN2A, GRIN2B, MAGI2, MEF2C, NEDDL4, NDP, NRXN1, PIGA, PLCB1, PTEN, SCA2, SCN1A, SETBP1, SIK1, SLC25A22, SLC35A2, SPTAN1, ST3Gal3, TBC1D24, TCF4, WWOX.
Commonly Associated Conditions
- Hypoxic-ischemic encephalopathy (HIE)
- Chromosomal disorders such as trisomy 21
- Brain malformation such as holoprosencephaly, malformations of cortical development (such as pachygyria or lissencephaly [including Miller-Dieker syndrome with deletion of 17p13.3], hemimegalencephaly, schizencephaly, heterotopia, and focal cortical dysplasia)
- Intraventricular/intraparenchymal hemorrhage
- Periventricular leukomalacia
- Tuberous sclerosis complex (TSC)
- Other neurocutaneous conditions such as neurofibromatosis type 1 (NF1), incontinentia pigmenti achromians (hypomelanosis of Ito)
- Disorders of X-linked inheritance such as Aicardi syndrome (Consider in girls with agenesis of the corpus callosum and chorioretinal lacunae.)
- Hydrocephalus of various causes
- Trauma (any but often nonaccidental)
- Progressive encephalopathy with edema, hypsarrhythmia, and optic atrophy syndrome
- Infections: meningitis/encephalitis, congenital infections (e.g., toxoplasmosis, rubella, cytomegalovirus, HIV)
- Inborn errors of metabolism such as Menkes disease, disorders of amino acid metabolism (such as phenylketonuria and maple syrup urine disease), pyruvate dehydrogenase complex deficiency, mitochondrial disorders (such as Leigh syndrome), pyridoxine-dependent seizures, glucose transporter protein type 1 (GLUT1) deficiency, and uncommonly, organic acidurias (such as methylmalonic aciduria)