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Introduction

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Infantile spasms, also known as infantile epileptic encephalopathy (IEE), is a severe form of childhood epilepsy that typically manifests within the first year of life and appears to be tied to a particular neurodevelopmental period. A high-amplitude, chaotic interictal electroencephalographic (EEG) background, known as hypsarrhythmia, is often seen in association with infantile spasms. In the wake of infantile spasms, the majority of children are left with significant cognitive delay. The triad of infantile spasms, developmental arrest or regression, and the characteristic EEG background of hypsarrhythmia has been dubbed West syndrome, after the English physician William West, who first provided a detailed description of spasms in 1841, as seen in his 4-month-old son.1 The broader term epileptic spasms is sometimes used to denote events of a similar semiology that tend to present in a slightly older age range and are not associated with hypsarrhythmia on EEG.

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Epidemiology

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The incidence of infantile spasms has been estimated to be between 0.25 and 0.42 per 1000 live births, with a slight predilection toward male infants over female.2 Higher geographic latitudes have been noted to be associated with a higher incidence of infantile spasms, although the extent to which this relationship may be due to environmental versus ethnic factors is unknown. The prevalence of infantile spasms ranges from 0.14 to 0.52 per 1000 children.3 Individuals tend to be affected sporadically by the disorder; only 1 to 7% of patients with infantile spasms have a family history of any type of epilepsy.

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Infantile spasms typically appear abruptly between the ages of 3 months and 1 year, with the peak age of onset ∼4 to 6 months and 90% of onsets prior to 12 months of age.4 Only 8% of children present after 2 years of age.4,5 Early onset is generally associated with increased mortality and poorer overall prognosis. Other seizure types, particularly partial seizures in cases of symptomatic infantile spasms, may precede, occur concurrently with, or follow the spasms. During the transitional period between infantile spasms and other seizure types, within one seizure episode a cluster of spasms may culminate in a focal seizure. The reverse may also be true, with an initial partial seizure triggering a series of spasms. In addition, the individual spasms may take on partial or tonic features, with asymmetric limb or head movements.

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Normal neurologic development is often reported prior to the onset of infantile spasms, although children whose spasms are symptomatic of other underlying causes may exhibit a baseline delay. However, a global decline becomes evident with the appearance of spasms. A marked decrease is commonly present in social interaction and responsiveness to sensory, particularly visual, stimuli. In line with these autistic tendencies, language delay is often seen later in development. In addition, axial hypotonia is reflective of a similar decline in motor functioning.

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Although infantile spasms may occasionally ...

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