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An epileptic spasm is a sudden flexion, extension or mixed flexion-extension of proximal and truncal muscles, lasting 1-2 seconds i.e. longer than a myoclonic jerk (which lasts milliseconds) but not as long as a tonic seizure (which lasts > 2 seconds). Spasms typically occur in a series, usually on wakening. Subtle forms may occur with only chin movement, grimacing, or head nodding. Spasms may be bilaterally symmetric, asymmetric, or unilateral, depending on whether they are generalised onset or focal onset.

CAUTION Epileptic spasms usually occur in a series (several in a cluster) right arrow if singular, consider other seizure types.

IMPORTANT epileptic spasms may occur as a generalized onset, focal onset or unknown onset seizure. They may also occur as a later feature in a seizure, rather than at onset. Shorter time to diagnosis and control of epileptic spasms is associated with better developmental outcomes in young children. Focal onset epileptic spasms have particular importance, as identification of a structural cause can allow consideration of curative epilepsy surgery. Clues to a focal origin of epileptic spasms include asymmetry of the motor features (especially in initial spasms in the cluster), lateral head/eye version, focal emphasis to the interictal or ictal EEG and presence of focal structural brain abnormality.

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