What Are the Symptoms and Causes of Infantile Spasms?

Medically Reviewed by Carol DerSarkissian, MD on October 14, 2021

The main symptoms of infantile spasms, also called West syndrome, are seizures and spasms. They don’t last very long -- only a few seconds. They happen in clusters. That means one follows right after another.

Seizures can be mild or forceful. Your baby may have more than one type. In a mild seizure, they might look like they're nodding their head. A more violent seizure might make them stiffen up, fling their arms out, and bring their knees up toward their body. Or their arms and legs might go straight out as they throw their head back. Some seizures only affect one side of their body. They might cry right before or right after they have a seizure.

Your baby may also seem to twitch or jerk a muscle. You might hear the doctor call this myoclonus. There are two types:

  • Positive myoclonus: They twitch because their muscles suddenly tense up.
  • Negative myoclonus: Their muscles suddenly relax.

Myoclonus is involuntary. That means it isn’t something your baby does on purpose. They can’t control when it happens. It’s like the sudden twitch or jerk you sometimes feel as you fall asleep.

West syndrome can affect your baby’s autonomic nervous system, the nerves in their body that control things that happen automatically, like their heartbeat and how wide their pupils are. During a seizure, your baby may:

  • Turn pale or turn red
  • Sweat
  • Have big pupils
  • Have watery eyes
  • Breathe faster or slower
  • Have a faster or slower heartbeat

As your baby grows, they reach milestones. They roll over, recognizes your voice, or puts things into their mouth. If your baby has West syndrome, it may take them longer to reach these points. Doctors call this delayed development.

They might also forget how to do things they already learned how to do. For example, it may seem like your baby forgot how to sit up. If they were chugging along and meeting milestones, they may seem to stop or slow down. Your doctor may call this developmental regression.

Even though they're tiny, there’s a lot of electrical activity going in your baby’s brain. If it’s abnormal, they might have seizures. Your baby’s doctor may use electroencephalography -- EEG for short -- to measure their brain activity while they're awake and asleep. They’ll put sticky tabs called electrodes on their head, and a machine will record the data they pick up. Babies with infantile spasms often have an abnormal pattern of electrical activity in their brains. It's called hypsarrhythmia.

The doctor might also want to do scans of their brain. Computed tomography (CT) and magnetic resonance imaging (MRI) scans create pictures that will let them see if there are any parts of it that haven’t formed the right way. These pictures can also show lesions, or places where injury or infection may have damaged their brain.

A condition called tuberous sclerosis is a common cause of West syndrome. It can cause noncancerous tumors that often look like colorless bumps on your baby’s skin. The doctor may use a special lamp to check for them.

Blood and urine tests can help the doctor figure out if your baby has an infection that’s causing West syndrome. The doctor might also want to do a lumbar puncture (you’ll often hear this called a spinal tap) and take some of the fluid out of their spine to check for meningitis. They can also use that fluid to see if a genetic problem is to blame for their West syndrome.

Anything that damages the brain can cause infantile spasms. Some of the causes happen before a baby is born, and some happen after birth.

The most common cause is an inherited condition called tuberous sclerosis complex. It makes noncancerous tumors grow in different body parts, like your baby’s brain, skin, kidneys, or other organs. If your baby has them, you might notice colorless bumps on their skin.

Genetic conditions like Down syndrome can cause these spasms, too. Or it could come from a noninherited problem with your baby’s genes.

Other causes of West syndrome include:

  • Brain injury
  • Problems with the way the brain formed
  • Changes in brain structure
  • Lack of oxygen to the brain
  • Brain infections
  • Lesions on the brain
  • Bleeding inside the skull
  • Inflammation in the brain (also called encephalitis)
  • Metabolism disorders
  • Vitamin B deficiency

Sometimes, doctors can’t find a cause for West syndrome. But there’s no evidence that it could be related to vaccinations or your baby’s sex.

Show Sources


Epilepsy Foundation: “Infantile Spasms,” “Infantile spasms (West’s Syndrome) and Tuberous Sclerosis Complex.”

National Institutes of Health National Center for Advancing Translational Sciences: “West syndrome.”

National Institutes of Health National Institute of Neurological Disorders and Stroke: “Myoclonus Fact Sheet.”

Cedars-Sinai: “West Syndrome.”

National Organization for Rare Disorders: “West Syndrome.”

National Institutes of Health, Genetics Home Reference: “Tuberous sclerosis complex.”

Medscape: “Infantile Spasm (West Syndrome).”

Nemours Foundation: “Infantile Spasms.”

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