Infantile spasms (IS) represent a rare but serious form of childhood epilepsy that affects the developing brain. This condition typically begins in the first year of life and is characterized by a specific type of seizure that can have a profound negative impact on an infant’s development. Understanding the frequency of this disorder is important, as prompt recognition and intervention are linked to better long-term outcomes.
How Common Are Infantile Spasms
Infantile spasms are considered a rare disorder, though they are the most frequently occurring catastrophic epilepsy syndrome in the first year of life. The incidence rate is estimated to be between 2.5 and 6.0 cases per 10,000 live births worldwide. This translates to approximately 1,200 to 2,500 new cases diagnosed annually in the United States alone.
The onset of spasms is highly age-dependent, with the vast majority of cases beginning before a child’s first birthday. The peak age for the initial appearance of spasms is consistently reported to be between four and eight months of age. Some studies have observed a slight male predominance, with males being affected at a slightly higher rate than females, sometimes reported as a 60:40 ratio.
Recognizing the Signs of Infantile Spasms
The characteristic presentation of infantile spasms often involves sudden, brief movements that occur in a rapid sequence called a cluster. These clusters commonly happen shortly after a baby wakes up from sleep. The individual spasms are quick, usually lasting only a second or two, but they repeat every few seconds for several minutes at a time.
A classic form of the spasm is known as a “salaam seizure” or “jackknife seizure” due to its appearance. This involves the infant suddenly bending forward at the waist, with the head and arms dropping down and the legs pulling up toward the abdomen. Other variations include extensor spasms, where the body stiffens and the head and limbs briefly throw back, or more subtle movements.
These subtle presentations, like a brief head nod, a wide-eyed blink, or a slight tummy crunch, are often misinterpreted by parents and even pediatricians. Because the movements can resemble a normal startle reflex (Moro reflex) or even colic, diagnosis is frequently delayed. Early recognition is important, as a developmental plateau or regression often accompanies the onset of the spasms.
The Underlying Causes
Infantile spasms are broadly categorized based on whether an underlying cause can be identified. The condition is termed symptomatic when a specific cause is found, which accounts for the majority of cases—typically 60% to 70%. These causes can be diverse, including structural brain abnormalities like cortical malformations, prior brain injuries from birth complications such as hypoxic-ischemic encephalopathy, or infections like meningitis.
A significant portion of symptomatic cases is linked to specific genetic syndromes, most notably Tuberous Sclerosis Complex (TSC), which is a common cause. Other cases are classified as cryptogenic (or sometimes idiopathic), meaning no underlying cause can be determined despite a thorough diagnostic evaluation. The cryptogenic category currently accounts for a smaller percentage of cases, ranging from approximately 10% to 40%. The identification of the cause has a direct bearing on the infant’s long-term developmental outlook, with cryptogenic cases often carrying a better prognosis.
Diagnosis and Treatment Protocols
The diagnostic workup for infantile spasms begins with a detailed review of the spells, often utilizing video recordings provided by the parents. The primary confirmation tool is an electroencephalogram (EEG), which measures the electrical activity of the brain. The EEG typically reveals a highly chaotic, disorganized, high-voltage pattern known as hypsarrhythmia, even when the infant is not actively seizing.
Once the diagnosis is confirmed, further testing focuses on identifying the specific underlying cause, as this guides the most effective treatment plan. This includes brain imaging, typically a Magnetic Resonance Imaging (MRI) scan, to detect structural abnormalities or brain lesions. Genetic testing is also performed to screen for known genetic conditions associated with the spasms.
Treatment for infantile spasms is considered an urgent matter due to the condition’s severe impact on neurodevelopment. The goal of treatment is to stop the spasms and normalize the abnormal hypsarrhythmia pattern on the EEG. The first-line pharmacological treatments include Adrenocorticotropic Hormone (ACTH) and vigabatrin. Vigabatrin is often the preferred initial choice when Tuberous Sclerosis Complex is identified as the underlying cause.