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  • Updated 04.27.2023
  • Released 01.21.1994
  • Expires For CME 04.27.2026

Infantile epileptic spasms syndrome



Infantile epileptic spasms syndrome (IESS) is a severe epileptic encephalopathy occurring in infancy. It encompasses both West syndrome as well as infants presenting with epileptic spasms and does not fulfill all the criteria for West syndrome (187). West syndrome classically comprises of a specific seizure type known as epileptic spasms, an interictal EEG pattern known as hypsarrhythmia, and psychomotor regression. Psychomotor regression or stagnation, or typical hypsarrhythmia, may not be apparent at onset, and therefore are not required to make the diagnosis of infantile epileptic spasms syndrome. It may result from various causes, but maturation of the brain is a crucial component. Early identification and proper treatment are required to optimize the outcome and avoid long-term disabilities. This updated article includes information on diagnoses, recently identified genetic causes, drug treatments, and outcome.

Key points

• Infantile epileptic spasms syndrome is one of the most recognized types of epileptic encephalopathy and constitutes a distinct form of epilepsy of early infancy.

• The disorder may present with a unique seizure type (spasms), a characteristic EEG pattern known as hypsarrhythmia, and psychomotor delay/arrest.

• Infantile epileptic spasms syndrome is often associated with many underlying disorders. However, no underlying cause can be detected in 10% to 40% of patients.

• Treatment of infantile epileptic spasms syndrome is mandatory because of poor outcome. Treatment is unconventional, with adrenocorticotropic hormone (ACTH), vigabatrin, and high doses of oral steroids being the most effective drugs.

• Effective treatment of infantile epileptic spasms syndrome should produce both cessation of clinical spasms and resolution of hypsarrhythmia on EEG and is an “all-or-none” response.

Historical note and terminology

In a letter to Lancet in 1841, West first described the infantile spasms his 4-month-old son suffered. He emphasized the relentless nature, especially in terms of psychomotor retardation (175). In 1952 Gibbs and Gibbs first described the unique EEG pattern recorded in a large number of infantile spasm patients: hypsarrhythmia (hypsos, from Greek, meaning "height," arrhythmia, from Greek, meaning "lack of rhythm"), which is characterized by random, high-voltage, nonsynchronous spikes and slow-wave activity (66). The condition was considered incurable until the serendipitous discovery that adrenocorticotropic hormone (ACTH) could control the seizures (153). The triad of infantile spasms, mental retardation, and hypsarrhythmic EEG pattern has been collectively called West syndrome since the 1960s (64), although two of those three features were considered sufficient to fulfill criteria. The more recent change in terminology by the International League Against Epilepsy (ILAE) to use the term infantile epileptic spasms syndrome emphasizes the importance of early diagnosis and therapy because shorter lag time to treatment is associated with better outcomes. Psychomotor regression or stagnation, or typical hypsarrhythmia is no longer required to make the diagnosis, as these features may not be apparent at onset. Typically, the spasms involve brief synchronous contractions of musculature of the neck, trunk, and extremities, lasting up to 5 seconds, and they frequently occur in clusters. These may or may not be accompanied by a brief loss of alertness consciousness and upward gaze deviation (06; 45; 180). Synonyms include “lightning” or “jackknife convulsions” and “salaam seizures” (06).

Officially, epileptic spasms was not recognized as a particular type of seizure until 2001 (20). The most current classification of seizures recognizes that infantile spasms may manifest or extend beyond the infantile period and uses the more encompassing term of “epileptic spasms” (16; 55). Epileptic spasms are now classified under focal, generalized, or unknown onset (55). The term infantile spasms is suitable to use for epileptic spasms occurring at an infantile age.

Poor outcomes associated with infantile spasms, including development of refractory epilepsy (including 10% to 15% of children with infantile spasms who may develop Lennox-Gastaut syndrome), mental retardation, and autism spectrum disorders (180), impose a significant long-term cost burden on families, the healthcare system, and society (132).

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