Infantile spasms are a rare but serious form of epilepsy affecting infants, often leading to devastating consequences for neurological development. Because the spasms can be subtle and easily mistaken for common infant behaviors, immediate recognition by parents and caregivers is important. The condition is considered an epileptic encephalopathy, meaning frequent seizure activity contributes to a decline in developmental progress. Acting quickly to identify and treat these seizures is paramount to minimizing potential developmental harm.
Defining Infantile Spasms
Infantile spasms are a specific type of seizure characterized by a sudden, brief stiffening or tensing of the body, typically occurring in clusters. This age-dependent epileptic syndrome usually begins between four and eight months of age. The spasms are a hallmark feature of West Syndrome.
West Syndrome is defined by a triad of clinical features: the spasms, a measurable loss or regression of developmental milestones, and a chaotic pattern on an electroencephalogram (EEG). The peak incidence is between three and seven months, though they can occur anytime within the first two years of life. The presence of infantile spasms combined with developmental regression signals a neurological emergency requiring urgent medical attention.
Recognizing the Physical Manifestations
Infantile spasms present as a sudden, rapid, tonic contraction of the trunk and limbs lasting only one or two seconds. They are classified into three main types: flexor, extensor, or a combination of both, which is the most common presentation. Flexor spasms cause the body to briefly bend forward, often described as a “jackknife” movement.
Extensor spasms involve the sudden stiffening and arching of the back, with the arms and legs extending outward. Mixed spasms combine these movements, such as the upper body flexing while the legs extend. The spasms nearly always occur in clusters, repeating every five to thirty seconds for several minutes, often multiple times a day. These clusters most frequently occur when the infant is transitioning between sleep and wakefulness, such as upon waking or after feeding. Parents may mistakenly attribute the movements to a normal startle reflex or colic, but unlike colic, the movements involve sudden stiffening rather than prolonged discomfort.
Identifying Underlying Etiologies
Infantile spasms are a seizure type arising from a wide range of underlying neurological disorders. Identifying the cause is a major step in determining both treatment and prognosis. Causes are broadly categorized into three groups: symptomatic, cryptogenic, and idiopathic.
Symptomatic spasms have an identifiable cause, accounting for up to 70% of cases. Causes include structural brain abnormalities (e.g., cortical dysplasia), genetic disorders (e.g., Tuberous Sclerosis Complex), or birth injuries (e.g., hypoxic-ischemic encephalopathy). Cryptogenic spasms are those where a cause is suspected due to pre-existing developmental delay, but remains unidentified after extensive testing.
Idiopathic spasms are the rarest category, occurring when the infant had normal development before onset and no cause is found despite comprehensive evaluation. This category is shrinking as genetic and imaging technologies advance. The prognosis is generally better for infants with idiopathic spasms compared to those with a known symptomatic cause.
Diagnosis and Confirmatory Testing
Diagnosis relies on clinical observation and specific electrophysiological testing, typically overseen by a pediatric neurologist. The central diagnostic tool is the Electroencephalogram (EEG), which records the electrical activity of the brain. The EEG captures the electrical signature of the spasms and looks for an abnormal background pattern.
The characteristic interictal (between spasms) pattern seen on the EEG is called hypsarrhythmia, a highly disorganized, high-amplitude, chaotic arrangement of spikes and slow waves. While hypsarrhythmia is strongly suggestive of the condition, its presence is not mandatory for diagnosis. To determine the underlying etiology, other tests are immediately ordered.
Magnetic Resonance Imaging (MRI) of the brain is essential to identify structural abnormalities or prior brain injury. Additionally, metabolic screenings and targeted genetic panels are used to find inborn errors of metabolism or specific gene mutations, such as those associated with Tuberous Sclerosis Complex.
Treatment Protocols and Long-Term Outlook
The primary goal of treatment is to achieve electroclinical remission: the complete cessation of visible spasms and the resolution of the hypsarrhythmia pattern on the EEG. Early intervention is time-sensitive because ongoing abnormal brain activity directly contributes to developmental regression and poor outcomes. The two main first-line medications are Adrenocorticotropic Hormone (ACTH) and Vigabatrin.
ACTH is a hormonal therapy administered by injection that suppresses spasms and hypsarrhythmia, though it carries a risk of significant side effects (e.g., high blood pressure, infection, weight gain). Vigabatrin is preferred for infants with Tuberous Sclerosis Complex, but it requires mandatory eye monitoring due to the risk of irreversible peripheral vision loss.
If first-line treatments are unsuccessful, second-line options include high-dose oral steroids or a medical Ketogenic Diet. The long-term outlook is highly variable, depending on the underlying cause and the speed of treatment. Infants with a normal developmental trajectory before onset and a rapid response to therapy have a better prognosis. Developmental delays and the later emergence of other forms of epilepsy, such as Lennox-Gastaut syndrome, are common complications.