Infantile spasms are a type of seizure that occurs in babies, typically in the first year of life. Each spasm lasts only one to two seconds, but they cluster together in groups with short pauses between them, often repeating for several minutes. Despite how brief they look, infantile spasms are considered a neurological emergency because delays in treatment can significantly harm a child’s cognitive development.
What the Spasms Look Like
The movements are sudden and brief. A baby might stiffen, arch their back, bend their arms and legs forward, or nod their head repeatedly. Some babies grimace, roll their eyes upward, or pull their head to one side. The whole thing can look so subtle that parents initially mistake it for a startle, a stomach cramp, or colic.
Spasms are categorized by the direction of the movement. Flexor spasms involve the baby folding inward, with the trunk curling forward and the arms pulling in. Extensor spasms are the opposite: the neck, back, and limbs extend outward. The most common type is mixed, where the trunk flexes forward while the arms and legs extend. In some cases, particularly in babies already receiving treatment, spasms can be extremely subtle, limited to eye movements, neck twitches, or brief pauses in activity.
The defining feature is clustering. Over two-thirds of babies have spasms that come in groups, sometimes one every four to five seconds. Within a cluster, the intensity often builds in a crescendo pattern, peaking and then tapering off. Clusters typically last several minutes. Babies often cry or seem distressed between spasms, which is another reason parents sometimes attribute the episodes to digestive discomfort rather than seizures.
When They Start
Most cases begin between three and twelve months of age, with a peak around four to six months. Onset after one year is uncommon. Parents often first notice the spasms happening shortly after the baby wakes up or during transitions between sleep and wakefulness, though they can occur at any time of day.
What Causes Them
In most cases, infantile spasms occur in babies who already have an underlying brain disorder or developmental condition. The list of potential causes is long, but the major categories include brain malformations present from birth, genetic or metabolic disorders, oxygen deprivation during labor or delivery, and serious head injuries around the time of birth.
Tuberous sclerosis complex, a rare hereditary condition that affects the brain, skin, and other organs, is one of the more commonly identified causes. Other genetic conditions including Down syndrome can also lead to infantile spasms. Infections acquired before birth, such as cytomegalovirus or Zika virus, are rarer triggers. In some babies, no underlying cause is ever found. These cases, previously called “cryptogenic,” generally carry a better prognosis.
How They’re Diagnosed
Diagnosis relies on an EEG, a test that records electrical activity in the brain. Medical guidelines recommend that when infantile spasms are suspected, an EEG should be performed within a few days. The hallmark pattern doctors look for is called hypsarrhythmia: chaotic, high-voltage brainwaves with spikes that shift unpredictably across different areas of the brain. This disorganized electrical activity is distinctly different from a normal infant EEG and confirms the diagnosis.
Because the spasms themselves can look like ordinary baby movements, many parents capture video on their phones before bringing their concerns to a doctor. This can be extremely helpful. Conditions like Sandifer syndrome, which involves back-arching and body twisting in response to acid reflux, can look similar on the surface but produce a completely normal EEG. The electrical recording is what separates infantile spasms from benign mimics.
Why Speed Matters
Treatment timing has a dramatic effect on outcomes. A study tracking children with infantile spasms of unknown cause found that 100% of those treated within one month of spasm onset achieved normal cognitive outcomes on long-term follow-up. Among children treated after a delay of one to six and a half months, only 40% reached normal cognitive levels. Once significant developmental regression had persisted for a month or more, the chance of full cognitive recovery dropped sharply.
This is why current guidelines emphasize that once an EEG confirms the diagnosis, treatment should begin immediately. The chaotic brain activity associated with infantile spasms appears to actively disrupt normal development for as long as it continues, so every week of delay carries real consequences.
How They’re Treated
Two treatments are considered standard: hormonal therapy (most commonly a hormone called ACTH, given by injection) and a medication called vigabatrin. Both aim to stop the spasms and normalize the EEG pattern.
ACTH has the strongest individual success rate. In a large prospective study across 22 U.S. centers, 55% of babies treated with ACTH had their spasms stop within two weeks and their EEG normalize by three months. Oral steroids achieved a 39% response, and vigabatrin alone reached 36%. However, combining hormonal therapy with vigabatrin pushed the success rate to 72%, compared to 57% for hormonal therapy alone, and babies on the combination also responded faster.
Vigabatrin is often preferred as the first choice when the underlying cause is tuberous sclerosis complex, where it tends to work particularly well. For other causes, hormonal therapy or a combination approach is more common.
Side Effects of Treatment
ACTH and steroids can cause irritability, high blood pressure, increased infection risk, and changes in appetite and sleep during treatment. These effects are generally temporary and resolve when the course ends.
Vigabatrin carries a more specific long-term risk: peripheral vision loss. In adults treated chronically, 30 to 40% develop some degree of permanent narrowing of their visual field. The vision loss is usually not severe enough to cause noticeable symptoms, but it is irreversible. For infants, who typically receive shorter courses, the risk is lower but still monitored carefully. Babies on vigabatrin need regular eye exams to watch for early signs of retinal changes.
What to Watch For
The biggest challenge with infantile spasms is recognizing them in the first place. Many parents describe a gut feeling that something wasn’t right, only to be reassured initially that the movements were normal. If your baby has brief, repetitive stiffening or jerking movements that come in clusters, especially around wake-up times, recording the episodes on video and seeking an evaluation promptly gives your child the best chance at a good outcome. The difference between early and late treatment is one of the starkest in pediatric neurology.