West syndrome: symptoms, causes and treatment

Short answer: West syndrome is a severe epilepsy of babies defined by three features: epileptic spasms, a chaotic brain-wave pattern on EEG called hypsarrhythmia, and development that stalls or goes backward.^1,2 It is the classic form of infantile spasms, it needs urgent assessment, and the usual first treatments are hormones (ACTH or prednisolone) or vigabatrin.^3,4

If you think your baby is having spasms, film an episode and contact your doctor the same day. This page explains what West syndrome is, why it happens, how it is diagnosed and treated, and what the research says about the outlook.

What is West syndrome?

West syndrome is named after William James West, a doctor who described the spasms in his own son in 1841.² Today it is defined by a triad:^1,2

1. Epileptic spasms, also called infantile spasms.
2. Hypsarrhythmia, a typical EEG pattern between spasms.
3. Developmental plateauing or regression, meaning the baby stops gaining skills or loses some.

Infantile spasms are a seizure type in babies. West syndrome is an epilepsy syndrome, the name for the whole picture.⁵ In one review, West syndrome was the presentation in about 90% of babies with infantile spasms.²

West syndrome and IESS

In 2022 the International League Against Epilepsy (ILAE) published a new classification of epilepsy syndromes that start before age 2.⁶ It uses the name infantile epileptic spasms syndrome (IESS) for epileptic spasms that begin between 1 and 24 months of age. IESS includes West syndrome, the group with the full triad.¹

The wider name matters for families. Not every baby with spasms has classic hypsarrhythmia, and doctors do not always agree on whether it is present. One expert review warns that a strict West syndrome definition could lead to standard treatment being wrongly withheld from babies who do not meet every criterion.⁵ Experts warn that babies with infantile spasms should still get standard treatment even if they do not meet every part of the triad.⁵

West syndrome symptoms

The spasms

Spasms start between 1 and 24 months of age, most often between 3 and 12 months, and boys are affected more often than girls.¹ The average age at onset is about 6 months.⁷

A typical spasm is a sudden bend forward of the neck and trunk with the arms drawn in. Spasms can also be a sudden stiffening (extension) or a mix of both. They are usually symmetric and come in clusters, often just after waking.^2,7 Each spasm lasts 1 to 2 seconds.⁸ One review notes that a baby may cry or scream just before or after a spasm.² Spasms are often confused with normal baby movements and other behaviors.⁷

Changes in development

Development may slow or go backward around the time spasms begin, so a baby stops gaining new skills or loses some.¹ One review says that in most babies some delay is present before the spasms start, though it is hard to recognize at that age.² Some babies keep developing normally.¹

West syndrome EEG: hypsarrhythmia

An EEG (a recording of the brain's electrical activity) is the key test. Between spasms, the classic finding is hypsarrhythmia: a chaotic mix of very large, slow waves with spikes that vary in size, shape and location.² Variants, called modified hypsarrhythmia, include patterns that are lopsided or have one main focus.⁹

The pattern can come and go. The ILAE says the abnormality is enhanced in drowsiness, in sleep and on waking.¹⁰ Long recordings also show it can fade in REM (dreaming) sleep and look more normal briefly on arousal.⁹ Either way, the EEG should include sleep. Experts recommend a prolonged video-EEG recorded awake and asleep if spasms are suspected.¹¹ Nearly all of 28 guidelines around the world recommend an EEG (27 of 28).⁴ The hypsarrhythmia page explains the pattern in more detail.

What causes West syndrome?

West syndrome is a symptom of something affecting the developing brain. In the UK Infantile Spasms Study, 127 of 207 babies (61%) had a proven cause, 33% had no cause found, and 6% were not fully tested.¹² The most common causes were:¹²

• Brain injury from lack of oxygen around birth (hypoxic-ischemic encephalopathy): 10%
• Chromosome conditions: 8%
• Brain malformations: 8%
• Stroke: 8%
• Tuberous sclerosis complex (TSC): 7%
• Injury or bleeding around the brain's fluid spaces (periventricular leukomalacia or hemorrhage): 5%

Many other causes were each uncommon. The ILAE also lists gene changes and metabolic conditions.¹ That is why doctors often order a brain MRI and, increasingly, genetic tests. Across world guidelines, 71% recommend an MRI and 54% genetic testing.⁴

West syndrome treatment

Treatment aims to stop the spasms and clear the hypsarrhythmia as fast as possible.⁷ The US consensus calls for early recognition, a short course of first-line treatment, a timely EEG to check response, and a quick change if it is not working.³

• Hormones. ACTH, given as an injection into the muscle, or oral prednisolone.^13,14 For spasms not caused by TSC, hormones stopped spasms in more babies than vigabatrin in trials.^15,16
• Vigabatrin. A medicine given by mouth, split into two doses a day.¹⁷ Every guideline in a 2026 global review recommends it first when TSC is the cause.⁴ It carries a boxed warning about permanent vision loss.¹⁷
• Judging response. Doctors usually decide within about two weeks, often with a repeat EEG.^3,4

Speed matters. In the UK trial, each step up in the delay to treatment was linked to a lower development score at age 4.¹⁸

Getting each dose right. Because response is judged within about two weeks, the dose a baby actually receives matters from day one.⁴ Every vigabatrin form is the same medicine.¹⁷ The ready-to-use liquid (labeled for infantile spasms from 1 month to 2 years, like the powder) needs no mixing; in one small study funded by its maker, doses prepared from it were more accurate than doses mixed from powder.^17,19

West syndrome life expectancy and outlook

The outlook varies widely, and the underlying cause is the strongest guide.²⁰

• Development. In studies with follow-up of up to 50 years, about one in four people had a favorable cognitive outcome and about one in three became completely seizure-free. Autism is relatively common.²⁰
• Spontaneous change. About one in four babies stop having spasms on their own within a year, but waiting is not a safe plan because delay is linked to worse development.^7,18
• Other seizure types. Some children go on to other epilepsies. A narrative review reports that 18% move on to Lennox-Gastaut syndrome, based on older cohorts.² Treatment that stops the spasms can also reveal other seizures that the spasms were hiding.¹³

Life expectancy

There is no single life-expectancy figure for babies diagnosed today. The risk of early death is higher than for other children and stays higher through life.²⁰ The published figures depend on the era of the study, the cause of the spasms and how long children were followed:

• Finland, children born 1960 to 1976. 31% had died after 20 to 35 years of follow-up.²¹ In a study of the same Finnish era followed for five decades, 49% of 207 children had died, at a mean age of 19. The risk of death was about five times higher when a cause was known than when none was found, and pneumonia was the most common cause of death.²²
• One US hospital, born 2000 to 2011. 17% of 150 children died during a median of 12 years.²³
• One center in India. 11.9% of 160 children had died after 10 years. Seizures other than spasms and a metabolic cause predicted higher risk, and none of the children without an identified cause died.²⁴
• Australia, population study. 2 of 64 infants (3%) with West syndrome, related spasm epilepsy or unifocal epilepsy had died by age 2.²⁵

These numbers come from groups treated decades apart and in different health systems, so they cannot predict any one child's future. Your child's neurologist can explain what the cause means for your child.

Questions to ask your baby's doctor

• Do the EEG and the spasms fit infantile spasms or West syndrome?
• What tests will look for a cause (MRI, genetic tests), and when?
• Which first treatment do you recommend, and why?
• When will we repeat the EEG to check whether it is working?
• If we use vigabatrin, which form should we use, and how do we measure each dose?

Related pages

• Infantile spasms and infantile spasms treatment
• Hypsarrhythmia: the EEG pattern
• Vigabatrin for infantile spasms and vigabatrin for tuberous sclerosis
• Vigabatrin side effects and research summaries