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Figure 1. Burst-suppression (15 mm/sec). This example is from a 15-day-old infant with
early myoclonic encephalopathy.

Severe epilepsy syndromes of infancy

In infancy (i.e. the period from one month to two years of age), the first epilepsy syndrome
described  West syndrome  occurs along with one of the most recently recognised epileptic
encephalopathies  Dravet syndrome. Even more recently a third syndrome  migrating focal
epilepsy of infancy  has been described.

West syndrome
West syndrome comprises a triad of epileptic spasms, mental retardation and hypsarrhythmia.
It usually starts between three and 12 months of age, with a peak at five months. Its incidence
is 35 per 10,000 and it is more common in boys.

The defining seizure type is epileptic spasms. This term is now preferred to infantile spasms,
recognising the fact that the seizure type can occur in older children. They consist of sudden,
brief contractions of axial and limb muscles lasting longer than myoclonic seizures (i.e.
longer than 100 milliseconds) and shorter than tonic seizures (i.e. shorter than a second 
although many would say shorter than two seconds). Characteristically they occur in clusters
which may include tens or even hundreds of individual spasms. Spasms may be flexor,
extensor or mixed flexor-extensor. The type does not appear to be important in terms of
aetiology or prognosis. They are usually symmetrical. However, asymmetrical spasms do
occur and often indicate focal structural brain pathology. Indeed a cluster of spasms may be
preceded by or be followed by a focal seizure. Spasms usually occur on arousal or when alert.
Exceptionally they occur during sleep. Loud noises, tactile stimuli and feeding may all
precipitate spasms. Early on in the course of the condition spasms may be very subtle and
infrequent (sometimes manifested with head nods), but tend to build up both in intensity and
frequency such that they eventually become obvious.

Prior to the onset of spasms, development may have been normal or delayed, reflecting the
underlying aetiology. Where development has been normal, parents often first notice a period
of social disengagement, particularly for visual stimuli. Developmental deterioration during
the period of active spasms is usual, but not universal. Most children who have had spasms
will eventually have severe learning difficulties, but up to 15% will show normal or near
normal development.