West syndrome is a severe form of epilepsy that appears in infancy, most often between 3 and 7 months of age. It affects roughly 1.6 to 4.5 out of every 10,000 babies born and is defined by three features occurring together: a specific type of seizure called infantile spasms, a chaotic pattern of brain activity visible on an EEG, and a stalling or reversal of the child’s development. Although onset can occur anytime from the first week of life up to about 4.5 years, the vast majority of cases begin in the first year.
The Three Defining Features
West syndrome is recognized by a triad of signs. The first, infantile spasms, are brief, sudden episodes where the baby’s trunk and neck flex forward and the arms pull inward. Each spasm lasts only a few seconds, but they tend to come in clusters, often right after the baby wakes up. A single cluster can contain dozens of spasms in a row, and parents sometimes mistake early episodes for colic, a startle reflex, or stomach pain.
The second feature is a distinctive EEG pattern called hypsarrhythmia. During this recording, the baby’s brain produces a disorganized mix of very high-voltage slow waves interrupted by random spikes that shift in location, size, and shape. It looks nothing like the organized rhythms of a healthy infant brain, and it can appear even between spasm clusters, which is why an EEG is essential for diagnosis.
The third feature is developmental arrest or regression. In a North Indian study that assessed children across physical, cognitive, communication, social, and daily living skills, over 96% of children experienced developmental regression after spasms began, and the vast majority scored low across all developmental domains rather than in just one area. Babies who were previously smiling, babbling, or reaching for objects may stop doing those things or lose skills they had already gained.
Why It Happens
West syndrome has many possible causes, generally grouped into three categories. Structural causes include brain malformations present from birth, brain injuries from oxygen deprivation during delivery, or damage from infections like meningitis. Genetic causes range from chromosomal conditions such as Down syndrome to specific gene mutations that disrupt brain development. Metabolic causes involve inherited disorders where the body cannot properly process certain nutrients or chemicals the brain needs to function.
One particularly well-known association is with tuberous sclerosis complex (TSC), a genetic condition that causes benign growths in the brain and other organs. Children with TSC who develop West syndrome tend to respond differently to treatment than children with other underlying causes, which influences the choice of therapy.
In a meaningful number of cases, no cause is ever identified despite extensive testing. These cases, sometimes called “cryptogenic,” generally carry a somewhat better outlook for development than cases with a confirmed structural or genetic cause.
Updated Terminology
The International League Against Epilepsy (ILAE) has proposed renaming the condition “Infantile Spasms Syndrome” to cover both the classic triad and cases where one or two features are missing. Not every child has clear hypsarrhythmia on EEG, for example, yet may still benefit from the same treatment approach. The change is intended to reduce diagnostic confusion, though many pediatric neurologists still use “West syndrome” because it is so widely recognized. Both terms refer to the same core condition.
How It Is Treated
Speed matters. The sooner treatment begins after spasms start, the better the chances of controlling seizures and limiting developmental harm. Two main first-line options exist: hormonal therapy and a medication that works specifically on a brain chemical called GABA.
Hormonal therapy uses either injected ACTH (a synthetic hormone that stimulates the body’s cortisol production) or high-dose oral prednisolone. Both are given in short, intensive courses, typically about two weeks of active treatment followed by a gradual taper over two more weeks. Studies show that higher doses of prednisolone work as well as ACTH injections, giving families a less invasive option. The initial response to hormonal treatment is often strong, though long-term control can be harder to maintain.
For children with tuberous sclerosis complex, a GABA-boosting medication called vigabatrin is the preferred first choice. It is given daily for about three months and then tapered over an additional month. Response typically appears within one to two weeks. Higher doses are more effective than lower ones. The main concern with vigabatrin is a risk of permanent visual field loss with prolonged use, so children on it need regular eye monitoring.
When First-Line Treatment Fails
If spasms persist after standard therapies, the ketogenic diet is one alternative that has shown promise. This high-fat, very low-carbohydrate diet changes how the brain gets its energy, and in children with infantile spasms, roughly half who started the diet were still on it at 12 months. Among those who stayed on, all experienced at least a 50% reduction in seizures, and nearly half saw improvement greater than 90%. Half of the children with hypsarrhythmia showed improvement on follow-up EEGs. Children under age 1 and those who had tried fewer medications beforehand tended to respond best. Side effects were manageable, including kidney stones and reflux in a small number of children.
Developmental Outlook
West syndrome carries a serious developmental cost. The regression that accompanies spasm onset rarely reverses completely, even when seizures are well controlled. In developmental assessments, the overwhelming majority of children show delays across the board, affecting movement, communication, thinking, social interaction, and self-care skills. Isolated delays in just one area are uncommon; the impact tends to be global.
That said, outcomes vary widely depending on the underlying cause, how quickly treatment started, and how well the child responded. Children with no identifiable cause and a rapid, complete response to initial therapy tend to have the best developmental trajectories. Children with significant structural brain abnormalities or genetic conditions generally face more persistent challenges.
Progression to Other Epilepsy Types
Between 20% and 50% of children with West syndrome go on to develop Lennox-Gastaut syndrome, another severe epilepsy type that typically emerges in early childhood. Lennox-Gastaut involves multiple seizure types, a different abnormal EEG pattern, and intellectual disability. In one long-term follow-up study, 49% of 98 children originally diagnosed with West syndrome eventually met criteria for Lennox-Gastaut. This transition is one reason neurologists monitor children closely even after infantile spasms resolve, watching for new seizure patterns and EEG changes over time.
Children whose spasms stop but who continue to have abnormal EEG activity are at higher risk for this progression. Ongoing developmental support, including physical therapy, speech therapy, and early intervention programs, plays an important role regardless of seizure outcome.