Infantile spasms (West syndrome)


Infantile spasms (IS) are a type of seizure seen in infancy. They occur as the main feature of a seizure syndrome known as West syndrome. Infantile spasms consist of an acute onset stiffening of the legs and arms while bending forward, although variations may occur. They may be asymmetrical. They are sometimes confused with the Moro reflex.

West syndrome is diagnosed when IS are present in clusters and in great numbers (up to 100 spasms in a cluster and sometimes many clusters a day), in infants usually with developmental delay, approximately 3 to 6 months of age (up to one year), and accompanied by hysarrhthymia (a high amplitude chaotic abnormal pattern) on EEG. Other seizure types are also seen in 30 to 50% of infants with this syndrome. Spasms usually stop as the child gets older, but other seizure types often take their place; 20 to 50% go on to have Lennox Gastaut syndrome. 75% of children with West syndrome have or will develop developmental delay/intellectual disability. 50% of children with West syndrome have some degree of cerebral palsy. [Mackay: 2004]


0.15 to 0.2 per 1000 children 10 years of age or younger. [Mackay: 2004]


There are two kinds of West Syndrome, symptomatic and asymptomatic. As prognosis varies greatly with the two types, it is important to make the distinction. In symptomatic infantile spasms, a specific etiology can be found in the history and physical or on further testing. Examples include hypoxic-ischemic damage to the brain, either pre- or post-natally, cortical brain malformations, metabolic disorders (e.g., maple syrup urine disease, pyridoxine dependency, nonketotic hyperglycemia, phenylketonuria), chromosomal abnormalities, neurocutaneous syndromes, infection, including prenatal infections such as CMV, and tumor. This symptomatic category has become the largest category (85-90% of children with IS) with the improvements in brain imaging and other diagnostic testing.

In the idiopathic category (10-15%), children with IS have normal development and neurological exams at the onset of the spasms and a good prognosis for growing out of them. In this group, IS are associated with poor developmental outcome mainly if the IS don't respond to medication. Therefore, early diagnosis and treatment may affect the outcome in this group of children. Some neurologists also identify a third group, cryptogenic, in which children are either abnormal in development or in their neurologic exam at the onset of the spasms, but no specific cause can be identified. These infants generally have a prognosis similar to those in the symptomatic group.


Treatment is generally by a pediatric neurologist in communication with the primary care provider. Treatment is pursued early and aggressively in infants with infantile spasms as the prognosis is extremely poor and early treatment may affect outcome. Treatment consists of prednisolone, vigabatrin, which appears to be particularly effective in children with tuberous sclerosis-related infantile spasms but may cause visual impairment, or occasionally ACTH for a period of weeks until spasms are greatly reduced or stop. (ACTH has many potentially lethal side effects, must be given IM on a daily basis, and is very expensive.) The EEG at this time is usually improved. The optimum duration of treatment and dose are not well delineated. [Mackay: 2004] Short term treatment of infantile spasms may improve long term prognosis.


Infantile spasm prognosis depends on the etiology of the spasms and whether or not there is developmental delay and an abnormal neurologic exam at the time of presentation. A good outcome is associated with a lack of etiology after testing, normal neurologic exam and development on presentation with spasms, older age at onset, shorter duration of time during which spasms occur and good response to treatment of spasms. Overall, intellectual disability is eventually present in 70-90% of children with infantile spasms, usually severe to profound intellectual disability. Symptoms of cerebral palsy are eventually evident in 50% of children with infantile spasms.

In the idiopathic group (10-15% of all children with infantile spasms), development and neurological exam are normal at onset. With ACTH treatment, 40-65% will have a complete or near-complete recovery.

In symptomatic or cryptogenic IS (85-90% of all children with infantile spasms) neurological or developmental abnormalities are present before the first seizure. In this group, complete or near-complete recovery is achieved by only 5-15%.


Information & Support

For Professionals

Infantile Spasms (NIH)

For Parents and Patients


Epilepsy Association of Utah
For individuals with epilepsy, families, and friends, this site offers newsletters, events, links, local and youth support groups, activities for kids, first aid for seizures, and more.

Epilepsy Foundation
A national organization that provides information about epilepsy; programs to improve epilepsy treatment; materials to assist in helping people with epilepsy find jobs; activities in schools to educate the public; activities to educate policymakers; funds for research; and news about conferences and other items of interest.


Infantile Spasms (
Several frequently asked questions and answers about infantile spasms.

Practice Guidelines

Hancock EC, Osborne JP, Edwards SW.
Treatment of infantile spasms.
Cochrane Database Syst Rev. 2008(4):CD001770. PubMed abstract

Helpful Articles

PubMed search for articles on Infantile Spasms in children for the last 3 years

Nabbout R, Dulac O.
Epileptic syndromes in infancy and childhood.
Curr Opin Neurol. 2008;21(2):161-6. PubMed abstract

Authors & Reviewers

Initial Publication: September 2008;
Current Authors and Reviewers (click on name for bio):
Author: Lynne M. Kerr, MD, PhD
Reviewer: Colin Van Orman, MD
Authoring history
(Limited detail is available on authoring dates before 2014.)
AAuthor; CAContributing Author; SASenior Author; RReviewer

Page Bibliography

Mackay MT, Weiss SK, Adams-Webber T, Ashwal S, Stephens D, Ballaban-Gill K, Baram TZ, Duchowny M, Hirtz D, Pellock JM, Shields WD, Shinnar S, Wyllie E, Snead OC 3rd.
Practice parameter: medical treatment of infantile spasms: report of the American Academy of Neurology and the Child Neurology Society.
Neurology. 2004;62(10):1668-81. PubMed abstract / Full Text