DESCRIPTION

• Infantile spasms (IS) are seizures in children 2 months to 2 years of age, commonly associated with West syndrome—a severe infantile developmental and epileptic encephalopathy often with poor epilepsy and developmental outcomes.
  • Characterized by sudden flexion, extension, or mixed flexion-extension of the neck, trunk, arms, and/or legs
  • Can be subtle such as a mild contraction of the abdominal muscles or subtle movements of the head, lower rip (“retch sign”), or eyes
  • Can occur singly but the clustering (often on awakening) is helpful for diagnosis; 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 electroencephalography (EEG) background disrupted by frequent multifocal spikes; however, because hypsarrhythmia or developmental delay may be absent, the more inclusive term, IS syndrome, is preferred over West syndrome.

EPIDEMIOLOGY

• The onset occurs in the 1st year of life in >90%, with peak onset in ages 4 to 8 months, mean of 6 months. Onset is rare after 18 months of age.
• The incidence is 2 to 3.5/10,000 live births.

PATHOPHYSIOLOGY

• Unknown
• In 70–80% of cases, a specific condition is associated with IS.

RISK FACTORS

COMMONLY ASSOCIATED CONDITIONS

• Hypoxic-ischemic encephalopathy (HIE)
• Tuberous sclerosis complex (TSC)
• 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
• Stroke
• Intraventricular/intraparenchymal hemorrhage
• Periventricular leukomalacia
• Rarely in other neurocutaneous conditions such as neurofibromatosis type 1 (NF1), incontinentia pigmenti achromians (hypomelanosis of Ito)
• Aicardi syndrome (Consider in girls with agenesis of the corpus callosum and chorioretinal lacunae.)
• Trauma (any but often early nonaccidental)
• Infections: meningitis, encephalitis (e.g., herpes simplex virus [HSV]), congenital infections (e.g., toxoplasmosis, rubella, cytomegalovirus, HIV)
• Rarely, inborn errors of metabolism such as Menkes disease, disorders of amino acid metabolism (e.g., phenylketonuria and maple syrup urine disease), pyruvate dehydrogenase complex deficiency, mitochondrial disorders (e.g., Leigh syndrome), pyridoxine-dependent seizures, glucose transporter protein type 1 (GLUT1) deficiency, and uncommonly, organic acidurias (such as methylmalonic aciduria)