Infantile spasms (IS), also known as West syndrome, are a severe and uncommon form of epilepsy that typically begins between four and eight months of age. This condition is classified as an epileptic encephalopathy, meaning the seizure activity itself contributes to cognitive and developmental impairments. IS is characterized by brief, repetitive seizures that often lead to a loss of previously achieved developmental milestones. Prompt recognition and immediate treatment are paramount, as delays can permanently impair brain development and lead to long-term intellectual disability.
Recognizing the Physical Signs
The seizures, known as spasms, are quick, symmetrical contractions of the neck, trunk, and limbs, each lasting only one to two seconds. These movements are often subtle, appearing as a slight head nod, a brief tensing of the body, or a sudden, wide-eyed stare. Due to their brief nature, caregivers may mistake them for the Moro reflex, colic, or a simple startle.
Spasms rarely occur in isolation and instead manifest in clusters, a defining characteristic of the condition. A cluster can involve a few spasms to over a hundred, repeating every five to 30 seconds, and may last for several minutes. These clusters most frequently occur when the infant is transitioning between sleep and wakefulness, such as upon waking.
Spasms are generally categorized into three types: flexor, extensor, or mixed. Flexor spasms cause the body to bend forward, resembling a “jackknife” or “self-hugging” motion. Extensor spasms involve the sudden extension of the head, trunk, and limbs, causing the infant to arch their back. The mixed form, which is the most common, often combines upper body flexion with lower body extension.
Identifying Underlying Causes
Infantile spasms are rarely without an underlying cause, with a factor identified in 60% to 70% of cases, categorized as symptomatic. The causes are diverse, encompassing any disorder that results in brain damage, occurring before, during, or after birth. Common etiologies include prenatal conditions like brain malformations, perinatal injuries such as hypoxic-ischemic encephalopathy, and postnatal causes like infections.
Genetic disorders account for a significant portion of cases, with over 100 individual genes associated with the condition. Tuberous Sclerosis Complex (TSC) is the most frequently identified cause, accounting for 10% to 30% of cases, where abnormal growths called tubers form in the brain and other organs. Other genetic syndromes include CDKL5 deficiency disorder and Down syndrome.
In a smaller percentage of infants, the cause remains unknown, historically termed cryptogenic or idiopathic. These infants typically experience normal development prior to the onset of spasms and show no structural abnormalities on imaging. The distinction between symptomatic and cryptogenic strongly influences both the treatment strategy and the long-term outlook.
Diagnostic Procedures
Confirmation of infantile spasms requires a comprehensive evaluation, with the electroencephalogram (EEG) being the definitive test. The EEG records the brain’s electrical activity using electrodes placed on the scalp, often requiring video monitoring to correlate physical spasms with electrical changes. This testing identifies the characteristic and highly disorganized electrical pattern known as hypsarrhythmia.
Hypsarrhythmia is a pattern of chaotic, high-amplitude, and multifocal epileptiform discharges strongly associated with infantile spasms. Although it is the electrical hallmark of the syndrome, it may not be present in all children or may only appear during sleep, necessitating a prolonged EEG study. The primary goal is to capture the spasm itself, which appears on the EEG as a high-voltage slow wave followed by a sudden, brief flattening of electrical activity.
Beyond the EEG, a battery of tests is initiated to identify the underlying cause, which directly informs treatment choices. Magnetic resonance imaging (MRI) of the brain is frequently performed to detect structural abnormalities or evidence of prior brain injury. Genetic testing and metabolic blood work are also used to screen for specific syndromes or disorders, which can be identified in up to 40% of cases with modern genetic sequencing.
Treatment and Management Strategies
Treatment of infantile spasms is time-sensitive and requires rapid intervention to stop the spasms and resolve the hypsarrhythmia pattern. The two first-line therapies are hormonal therapy and the anti-epileptic medication vigabatrin. Adrenocorticotropic hormone (ACTH) is administered via injection and is highly effective at stopping spasms and normalizing the EEG. Oral corticosteroids, such as prednisolone, are also used as a form of hormonal therapy.
Vigabatrin is an oral medication that works by increasing the concentration of gamma-aminobutyric acid (GABA), a neurotransmitter that inhibits electrical activity in the brain. This drug is the preferred first-line treatment for infants whose spasms are caused by Tuberous Sclerosis Complex (TSC). For other etiologies, ACTH and oral steroids often show superior initial effectiveness compared to vigabatrin.
If initial therapy fails to achieve seizure freedom, physicians may switch to the other first-line option or consider combination therapy. Other management options include the ketogenic diet, a high-fat, low-carbohydrate regimen that alters brain metabolism. In rare cases where spasms are linked to a specific, localized brain lesion, epilepsy surgery to remove the affected area may be considered.
Developmental Outlook
The long-term developmental outlook for an infant with spasms is highly variable and directly tied to the underlying cause and treatment response speed. Infants with a symptomatic cause, such as a major brain malformation, face a poorer prognosis and a high likelihood of intellectual and neurodevelopmental disability. Conversely, infants with no identifiable underlying cause who had normal development before the spasms began have a greater likelihood of a favorable outcome.
Despite successful treatment, most children with a history of infantile spasms will experience some degree of developmental delay or intellectual disability. A favorable cognitive outcome is observed in approximately one-quarter of patients. About 50% to 70% will also develop other types of epilepsy later in childhood, and the risk of developing Lennox-Gastaut Syndrome is elevated.
The goal of treatment is to stop the seizures and minimize the developmental regression that often accompanies the onset of spasms. Early diagnosis and prompt, effective treatment offer the best chance for improving the overall neurodevelopmental trajectory. Even when spasms resolve, ongoing monitoring and developmental support are necessary to address potential long-term challenges in areas like speech, motor skills, and learning.