West Syndrome (Infantile Spasm)

West syndrome

Background

Severe epilepsy syndrome with the triad:
- Infantile spasm
- Hypsarrhythmia
- Mental retardation
Onset: 90% in the first 12 months after birth, with a peak onset between 4 and 6 months
Incedence: 3 to 5/10,000 live births
2% of childhood epilepsies
Classified according to etiology (old International League Against Epilepsy (ILAE) classification)
- Symptomatic (almost any disorder than can cause brain damage) ie:
  - Trisomy 21 (Down syndrome)
  - Trauma
  - Infectious (meningitis, encephalitis)
  - Metabolic disorders (ie maple syrup urine disease, mitochondrial encephalopathy, pyridoxine dependency)
  - Hydrocephalus/microcephaly
  - Tuberous sclerosis
  - Ischemic encephalopathy
- Cryptogenic
  - If a symptomatic cause is most probable, however the cause is not identified.
  - 8-42% of the West syndromes
- Idiopathic
  - 9-14% of the West syndromes
  - In contrast to cryptogenic West, there is a normal development until the onset.
  - No MRI abnormalities
New International League Against Epilepsy (ILAE) classification:
- Genetic
- Structural/metabolic
- Unknown

Psychomotor arrest or regression
Spasms, sudden contraction of the trunk en limb lasting around 2 - 10 seconds
- Flexor spasm (Salaam spasm): Rapid bending of the head and torso forward and simultaneous raising and bending of the arms, similar to the greeting between muslims (Salaam)
- Extensor spasm: Extension of the neck and trunk and with extension and abduction of the limbs
- Mixed spasm
1 to 30 clusters/day of 20 to 100 spasms each cluster

Interictal:

Hypsarrhythmia: high voltage, chaotic, slow waves and spikes in all cortical areas. The spikes originate from multiple foci and have no rhythmical or repetitive organization.
The typical hypsarrhythmia is usually seen in the early stage of West syndrome
The EEG gradually evolves to a more synchronized, with increased hemispheric synchronization en symmetry.
Hypsarrhytmia is most pronounced in sleep and the patients have reduces or absent non-REM sleep.
Other interictal patterns: diffused (encephalopathic) or focal slowing, multifocal Spike slow wave complex
The EEG can evolve towards a EEG seen in Lennox Gastaut syndrome

Ictal EEG

High-voltage, frontal dominant, generalized slow-wave transient followed by voltage attenuation

West syndrome with hypsarrhytmia (multifocal spike and slow waves, with little organization) in a 8 months old girl (average)