Infantile spasms are a rare but serious type of seizure that affects babies, typically starting between 3 and 12 months of age. These brief muscle spasms may look like startling movements, but they require urgent medical attention as early diagnosis and treatment are critical to protecting a baby’s developing brain.

Epidemiology

Infantile spasms are not common, but when they occur, they demand immediate attention from healthcare providers and families. According to available data, there are fewer than 1 case per 1,000 live births in the United States each year.^[1] This means that while the condition is rare, approximately 1,200 to 2,000 infants are affected annually in the United States alone.^[20]

The condition typically begins during the first year of life. Most cases start between 3 and 12 months of age, with the peak onset occurring between 4 and 8 months.^[1][5] While the spasms can technically begin any time during the first two years of life, and later onset cases have been documented, they are most characteristic of infancy. The timing of onset is important because a baby’s brain is developing rapidly during these early months, which makes prompt recognition and treatment especially crucial.

Causes

The causes of infantile spasms are diverse and complex. In fact, more than 200 different clinical conditions have been associated with this seizure disorder, which has led researchers to believe there must be some common pathway these various conditions share that leads to the development of spasms.^[6] Understanding what causes infantile spasms in a particular baby is important because it can guide treatment decisions and help predict outcomes.

It is estimated that approximately two out of three infants with infantile spasms have an identifiable cause for their seizures.^[4] These causes can be broadly grouped into several categories. Problems with how the brain developed in the womb are one major category. This includes brain malformations such as cortical dysplasia (abnormal development of the brain’s outer layer) or lissencephaly (a condition where the brain has a smooth appearance instead of normal folds and grooves).^[1]

Genetic conditions represent another important cause. These may be inherited from parents or occur as new, random changes. Examples include Down syndrome, Aicardi syndrome, tuberous sclerosis, and neurofibromatosis.^[1] More and more specific gene mutations are being linked to infantile spasms as genetic research advances.^[15]

Brain injuries are also a significant cause. These can happen before, during, or after birth. A lack of oxygen to the brain during delivery, known as hypoxic-ischemic encephalopathy, can lead to infantile spasms. Similarly, a perinatal stroke (when blood flow to part of the baby’s brain is blocked around the time of birth) may trigger spasms.^[1]

Infections affecting the brain can also be responsible. These include meningitis and infections caused by various viruses and bacteria, such as syphilis, Zika virus, and cytomegalovirus.^[1] Problems with the body’s metabolism—how it uses energy—can also cause spasms. These include inborn errors of metabolism and vitamin B6 deficiency, which in rare cases can be the sole cause of a baby’s spasms.^[15]

Abnormal blood vessels in the brain, such as hemangiomas or arteriovenous malformations, are additional potential causes.^[1] However, in some cases, despite thorough investigation, doctors cannot identify a specific cause for the spasms. These cases are sometimes referred to as having an unknown or cryptogenic origin.

Risk Factors

Certain factors can increase the likelihood that a baby will develop infantile spasms. Understanding these risk factors can help parents and healthcare providers remain vigilant for early signs of the condition. Some risk factors are present around the time of birth. Babies who are born with a low birth weight face an increased risk.^[1]

Birth complications that deprive the baby’s brain of oxygen are another significant risk factor. This can happen if there are problems during labor and delivery that restrict blood flow to the baby. Very low blood sugar in newborns, known as neonatal hypoglycemia, also increases risk.^[1]

Other risk factors may develop after a baby is born. A serious head injury from an accident or trauma can trigger infantile spasms.^[1] Brain infections that occur during infancy are another risk factor. Brain tumors, though rare in infants, can also lead to spasms. Even near-drowning incidents, which cause the brain to go without oxygen for too long, may result in this condition.

It is important to note that there is no evidence linking certain factors to infantile spasms. Family history of seizures, the baby’s gender, and immunizations have not been shown to be connected to the development of infantile spasms.^[4] This information can help alleviate concerns parents might have about routine medical care or family patterns.

Symptoms

Recognizing the symptoms of infantile spasms can be challenging because the movements may be subtle and are sometimes mistaken for normal baby behaviors. Each spasm is brief, lasting only about one to two seconds, but the pattern and characteristics of these movements are distinctive once you know what to look for.^[1][8]

The spasms can take several forms. The most common pattern includes sudden stiffening of the body or brief tensing of muscles. A baby might bend forward suddenly, with the head dropping down and the arms and legs drawing in. This is sometimes described as a “jackknife” movement.^[2] Alternatively, the baby’s back might arch, with the head thrown backward and the arms and legs straightening out.

More subtle signs can also occur. These might include just a head nod, a grimacing expression, the chin twitching, eyes rolling upward, or a brief wide-eyed stare.^[1][8] Some spasms only affect one side of the baby’s body. Because these movements can be so brief and subtle, they are sometimes mistaken for a startle reflex, colic, reflux, or hiccupping.^[15]

A key characteristic of infantile spasms is that they typically occur in clusters. This means multiple spasms happen in succession, usually with short pauses of five to ten seconds between each one.^[1] A cluster might last several minutes, and during that time, a baby could have dozens of individual spasms. Some babies have only a few spasms per day, while others may experience up to 100.^[1]

The timing of when spasms occur is also important. They most commonly happen just after a baby wakes up from sleep, whether in the morning or from a nap. They rarely occur during sleep itself.^[5] Parents often first notice the spasms during these transition periods when their baby is waking.

After a cluster of spasms, babies may show various reactions. Some cry, though not always. Many babies show decreased social interaction or stop smiling as much as they used to. Some become unusually fussy, while others become oddly quiet.^[1] During a cluster, some children cry briefly after each spasm, while others may seem distressed throughout. Interestingly, some babies actually smile or giggle after each spasm. Once a cluster ends, most children return to their normal behavior.

Developmental changes often accompany the spasms. Parents may notice that their baby stops doing things they had learned to do, such as rolling over, sitting up, crawling, or babbling.^[5] This loss of previously acquired skills, called regression, is particularly concerning and should prompt immediate medical evaluation. Other developmental problems might include decreased alertness or responsiveness to their surroundings.

Prevention

Because infantile spasms have so many different possible causes, there is no single prevention strategy that can eliminate all risk. However, certain measures during pregnancy and early infancy may help reduce the likelihood of conditions that can lead to infantile spasms.

Good prenatal care is fundamental. This includes regular checkups during pregnancy, proper nutrition, and avoiding harmful substances. Preventing infections during pregnancy can be important, as some brain infections that develop before birth have been linked to infantile spasms. Following recommended vaccination schedules for pregnant women and newborns can help prevent certain infections.

Safe delivery practices and proper management of labor complications can help prevent birth injuries that might lead to brain damage and subsequent spasms. Ensuring adequate oxygen supply to the baby during delivery is particularly important. Prompt treatment of any medical problems in newborns, such as very low blood sugar levels, can also help reduce risk.

After birth, protecting babies from head injuries is important. This includes proper use of car seats, safe sleeping practices, and preventing falls. If a baby develops a brain infection, prompt diagnosis and treatment may help minimize brain damage. For babies with known genetic or metabolic conditions that increase risk, close monitoring by specialists may allow for earlier detection if spasms do develop.

While these measures cannot prevent all cases of infantile spasms, they represent good general practices for protecting infant health. Perhaps the most important aspect of “prevention” in the context of infantile spasms is actually early detection and rapid treatment once spasms begin, as this can prevent further harm to the developing brain.

Pathophysiology

Understanding what happens in the brain during infantile spasms helps explain why this condition is so serious and why it requires urgent treatment. Pathophysiology refers to the changes in normal bodily functions that occur with a disease—in this case, the abnormal electrical activity in the brain that leads to seizures and impacts brain development.

Infantile spasms occur when parts of a baby’s brain are not working as they should, or when problems affect the whole brain. The spasms themselves are a type of seizure, which means they result from abnormal electrical activity in the brain.^[8] During a seizure, nerve cells in the brain fire electrical signals in an uncontrolled, excessive manner instead of in their normal, coordinated patterns.

One of the unique features of infantile spasms is the characteristic brain wave pattern often seen on an electroencephalogram (EEG), a test that records the brain’s electrical activity. Many babies with infantile spasms show a pattern called hypsarrhythmia.^[1] This pattern consists of chaotic, disorganized brain waves with high-voltage spikes and slow waves occurring asynchronously—meaning different parts of the brain are not working together in a coordinated way.^[6]

During an actual spasm, the EEG shows something called an electrodecremental response, which is essentially a flattening of the brain waves.^[6] This unusual pattern during the seizure itself is quite different from what is seen in other types of seizures.

When infantile spasms occur along with hypsarrhythmia on the EEG and developmental problems (either delay or loss of skills), this combination is called West syndrome. Not all babies with spasms have all three features of West syndrome, but they are closely related conditions.^[1]

The impact on brain development is profound. The young brain is extremely active during infancy, forming connections between nerve cells at a rapid pace. This process is essential for learning, memory, movement, and all aspects of development. When infantile spasms occur, the abnormal electrical activity disrupts these normal developmental processes. The seizures themselves, along with the abnormal background brain wave patterns seen between seizures, can directly contribute to cognitive and behavioral problems.^[4]

This is why infantile spasms are considered an epileptic encephalopathy—a condition in which the seizure activity itself contributes to worsening brain function and developmental problems.^[14] The longer the abnormal activity continues, the more harm it can cause to the developing brain. This understanding explains why early diagnosis and aggressive treatment are so critical. Even a delay of days or weeks in starting treatment can result in permanent brain injury.^[1]