[5] Such spasms are found in association with characteristic abnormal EEG pattern findings (hypsarrhythmia), and cognitive delay or deterioration.

[2][7] Epileptic spasms are commonly classified as symptomatic when a potential cause can be identified, or as cryptogenic if not (though these designations are used inconsistently).

[5] The spasms present as episodes of brisk (0.2-2s[5]) neck flexions-extensions and upper limp abductions-adductions,[2] lower limb extension, and trunk musculature contractions,[4] accompanied by upward deviation of the eyes.

[2] The onset of epileptic spasms is often associated with developmental regression: autistic withdrawal, and loss of social smiling and of visual attention.

[5] Based on etiology, cases of IESS are commonly classified as either symptomatic or cryptogenic - although these terms have not been used consistently.

Cryptogenic cases are thus contrastingly defined as those in which no specific cause can be identified, or where no such lesions or abnormalities were noted prior to syndrome onset.

[citation needed] A child with Down syndrome presenting with seizures that are difficult to control should be assessed for autistic spectrum disorder.

[2] Therapy with vigabatrin is also commonly undertaken (though long-term use is associated with a risk of visual field loss);[13] vigabatrin is considered the treatment of choice for infantile spasms associated with tuberous sclerosis complex, and is also favoured in those with serious brain lesions or malformations.

[14] Small epileptic foci augur a favourable outcome, however, in most cases, resection of extensive multilobar cortical dysplasias is called for, resulting in limited cognitive improvement.

Unfavourable prognostic factors include: symptomatic aetiology, early onset (prior to 3 months), presence of other seizure types prior to onset of infantile spasms, poor treatment response, EEG asymmetry, absence of typical hypsarrhythmia, and (prolongued) developmental regression.

[8] Whereas some 80% of all individuals with IESS will exhibit residual neurodevelopmental impairment, the figure falls to only a third for cryptogenic cases.

[2] Brisk initiation of therapy appears to be associated with more favourable neurodevelopmental outcomes - especially in cryptogenic cases.

[8] In about one quarter to one third of children with IESS, seizures will subside completely with time; such resolution is more common when the cause is cryptogenic.

Finally, a third will experience a deterioration with the appearance of additional recalcitrant seizure types - often evolving into Lennox–Gastaut syndrome.

It is believed that early aggressive treatment of infantile spasms can often prevent the later development of autistic features, or lessen their severity.