West syndrome. Infantile spasms
Incidence
Prevalence is around 1:3200 to 1:3500 of live births. Statistically, boys are more likely to be affected than girls at a ratio of around 5:4.
Clinical Characteristics
West syndrome (or infantile spasms) is characterized by the association of clusters of axial spasms, psychomotor retardation and an hypsarrhythmic interictal EEG pattern. It is the most frequent type of epileptic encephalopathy. It may occur in otherwise healthy infants (idiopathic) and in those with abnormal cognitive development or neurological damage (symptomatic). It is considered an epileptic syndrome. Infantile spasms, like many other ‘electroclinical syndromes’, have lots of different causes. A particular or specific cause will be found in seven or eight children out of every 10 children with West syndrome (symptomatic). The spasms consist of sudden axial flexion or, more often, extension movements and may be associated with ocular deviation. The contractions are most visible in the upper limbs and are frequently followed by crying. However, the spasm may be restricted to an upwards ocular deviation. A cerebral malformation should be considered in the presence of asymmetry. The spasms occur in a series, separated by intervals of 5-30 seconds, and may last for more than 10 minutes. The spasms become more intense as the series progresses. The EEG pattern of the spasms consists of a high-amplitude and diphasic slow wave. The interictal EEG pattern is described as hypsarrhythmic as it is characterised by asynchronous and high-amplitude slow waves and multifocal spikes. Both fast and slow variants, depending on the aetiology, have been reported. The aetiology of the syndrome is variable. Cerebral anomalies are detected in 70-80% of cases (symptomatic cases). The most common causes of these anomalies are malformations (most frequently tuberous sclerosis (Bourneville disease), or sequelae of ischemia or meningoencephalitis), a genetic anomaly (such as trisomy 21, the 1p36 deletion or mutations in the ARX or STK9 genes) or a metabolic disease (such as a mitochondrial disorder or phenylketonuria). Around 10% of cases of West syndrome are idiopathic: in these infants psychomotor development is normal before onset of the spasms and the contractions and hypsarrhythmia are symmetric and respond to medication. The remaining 10-20% of cases are cryptogenic and probably associated with an anomaly that has not yet been detected. Diagnosis is based on the clinical picture and EEG pattern. Treatment is pharmacological. The two most effective treatments are vigabatrin (often used as the first-line treatment) and corticoids (used when treatment with vigabatrin fails) as well as nitrazepam. Treatment should begin as early as possible to limit the cognitive deficit caused by the epilepsy. Surgical intervention is only used in cases with localised cerebral lesions. The prognosis varies depending on the etiology and speed with which treatment is initiated. Even after a first response to treatment, reoccurrence occurs within 6 months in 30% of cases. The spasms tend to resolve after 5 years of age but reoccurrences have been reported. Motor, sensorial or mental sequelae are present in 75% of infants and the epilepsy is resistant to medication in 50-60% of cases.
Precipitants
Drowsiness, lack of sleep. Spasms tend to occur upon awakening or after feeding.
Provocation Tests
An EEG is mandatory to confirm the diagnosis. No specific provocation test is available.
Diagnostic Procedures
It is an electro-clinical diagnosis. The diagnosis of infantile spasms is made by a combination of the typical features with a typical EEG. The EEG shows a very disorganised pattern termed ‘hypsarrhythmia’. The EEG is always abnormal in children with West syndrome but sometimes this abnormality is seen only during sleep. Most children with infantile spasms will need a number of tests (EEG, imaging studies, blood tests, urine tests and, sometimes, spinal fluid and other tests) in order to try to identify the underlying cause.