West syndrome

Puja Patel MD (Dr. Patel of Einstein College of Medicine and Montefiore Medical Center has no relevant financial relationships to disclose.)
Jerome Engel Jr MD PhD, editor. (

Dr. Engel of the David Geffen School of Medicine at the University of California, Los Angeles, received honorariums from Cerebel for advisory committee membership.

Originally released January 21, 1994; last updated November 3, 2020; expires November 3, 2023


West syndrome is a severe epileptic encephalopathy occurring in infancy that comprises specific seizure types consisting of spasms and interictal EEG pattern known as hypsarrhythmia, together with psychomotor regression. It may result from various causes, but maturation of the brain is a crucial component. Early identification and proper treatment are required, although not sufficient, 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


• West syndrome, or infantile spasms, is 1 of the most recognized types of epileptic encephalopathy and constitutes a distinct form of epilepsy of early infancy.


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


• Infantile spasms are often associated with many underlying disorders (infantile spasms due to structural/metabolic etiologies). However, no underlying cause can be detected in 10% to 40% of patients (infantile spasms from unknown causes).


• Treatment of infantile spasms 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 spasms should produce both cessation of 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 (West 1841). 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 (Gibbs and Gibbs 1952). The condition was considered incurable until the serendipitous discovery that adrenocorticotropic hormone (ACTH) could control the seizures (Sorel and Dusaucy-Bauloye 1958). The triad of infantile spasms, mental retardation, and hypsarrhythmic EEG pattern has been collectively called West syndrome since the 1960s (Gastaut et al 1964), although 2 of those 3 features are currently considered sufficient to fulfill criteria. 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 (Appleton 1993; Dulac 2001; Wong and Trevathan 2001). Synonyms include “lightning” or “jackknife convulsions” and “salaam seizures” (Appleton 1993).

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” (Berg et al 2010; Fisher et al 2017). Epileptic spasms are now classified under focal, generalized, or unknown onset (Fisher et al 2017).

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 (Wong and Trevathan 2001), impose a significant long-term cost burden on families, the healthcare system, and society (Pellock et al 2010).

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