West syndrome (or infantile spasms) is characterised 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 and in those with abnormal cognitive development.
The incidence is estimated at between 1 and 1.6/100,000 live births. Boys are more often affected than girls.
Onset occurs between 3 and 7 months of age in 50-70% of cases. Onset at birth or in older infants and children (up to the age of 5) is much less common. 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. 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.
The differential diagnosis may be problematic and should include Sandifier syndrome, benign myoclonus, hyperekplexia (see these terms), gastro-oesophageal reflux and breath holding spells.
Genetic counselling may be useful depending on the aetiology.
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). 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 aetiology 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.
Last update: March 2007