Infantile Spasms (IS) / West Syndrome
Infantile Spasms (IS), also known as West Syndrome, is a rare but severe epileptic encephalopathy of infancy. It is defined by a triad of clinical features: infantile spasms, developmental arrest or regression, and a characteristic EEG pattern called hypsarrhythmia. The ILAE classifies it as a developmental and epileptic encephalopathy, emphasising that the seizures themselves contribute to and exacerbate the developmental delay.
Presentation and Clinical Features
Age of Onset: IS typically begins in the first year of life, with a peak onset between 4 and 8 months of age.
Seizure Characteristics: The seizures are known as spasms and are typically brief, lasting 1-2 seconds. They are often subtle initially and can be easily missed or mistaken for colic or startle reflexes.
Semiology: Spasms can be flexor (head nodding, body jackknifing), extensor (arching of the back with splayed limbs), or a mixture. A classic flexor spasm is sometimes called a “salaam attack” due to its resemblance to a bow.
Frequency: Spasms often occur in clusters upon awakening from sleep or after a feed. The clusters may increase in frequency and intensity over time.
Developmental Impact: The epileptic activity has a profound effect on the developing brain. Infants with IS often show developmental arrest or regression, losing previously acquired skills like smiling or rolling over. This is a critical indicator that should prompt immediate investigation.
Etiology: The cause is diverse and can be classified as symptomatic, genetic, or cryptogenic (cause unknown).
Symptomatic: The majority of cases are due to a known brain injury or malformation, such as hypoxic-ischemic encephalopathy (HIE), perinatal stroke, cortical dysplasia, or neurocutaneous syndromes like Tuberous Sclerosis Complex.
Genetic: Gene mutations (e.g., STXBP1, KCNQ2) and chromosomal abnormalities (e.g., Down’s Syndrome) are also common causes.
Investigation
Diagnosis: The diagnosis is based on the clinical history of spasms, developmental arrest, and the characteristic EEG finding.
EEG: An urgent EEG is essential. The hallmark finding is hypsarrhythmia, which is a highly chaotic, disorganised, high-amplitude pattern of spike-and-wave discharges. If a routine EEG is inconclusive, a sleep EEG is vital as hypsarrhythmia is most prominent in non-REM sleep.
Investigations for Underlying Cause:
MRI Brain: This is crucial to identify any structural brain abnormalities.
Genetic Testing: Chromosomal microarray and gene panels (especially for epilepsy-related genes) are increasingly used.
Metabolic Screening: Tests for metabolic disorders, including lactate, ammonia, and amino acids, may be indicated in some cases.
Other: A thorough physical examination is needed, including a Wood’s lamp examination to look for hypomelanotic macules, which can indicate Tuberous Sclerosis Complex.
Management and Prognosis
Urgent Treatment: IS is considered a medical emergency. Prompt diagnosis and treatment are essential to improve the neurodevelopmental outcome.
First-Line Treatment: The UK’s National Institute for Health and Care Excellence (NICE) guidelines, informed by trials like UKISS, recommend a choice between hormonal therapy and Vigabatrin.
Hormonal Therapy: Prednisolone is the most common corticosteroid used in the UK. ACTH and hydrocortisone are also options.
Vigabatrin: This is a highly effective treatment, particularly for infants with Tuberous Sclerosis Complex, for whom it is the first-line monotherapy.
Combination Therapy: Some centres may use a combination of Prednisolone and Vigabatrin, which may offer a higher chance of seizure freedom.
Prognosis: The prognosis for seizure control and neurodevelopmental outcome depends heavily on the underlying cause and the speed of treatment.
Excellent Prognosis: Infants with a cryptogenic (unknown) cause and those with IS that responds quickly to treatment tend to have a better outcome.
Poor Prognosis: Cases with a structural brain abnormality often have a poorer prognosis, with a high chance of persistent developmental disability and progression to other epilepsy syndromes like Lennox-Gastaut Syndrome.
Long-Term Management: Even if spasms are controlled, most children are left with some degree of developmental disability. They often require ongoing support from a multidisciplinary team, including physiotherapists, speech therapists, and educational support.