Infantile spasms is a unique, and frequently malignant, epileptic syndrome confined to infants. This syndrome has three characteristic features:15,16

  • brief tonic seizures
  • hypsarrhythmic electroencephalograms (EEGs)
  • mental retardation

The triad of infantile spasms, hypsarrhythmic EEG, and mental retardation is referred to as West syndrome. Not all infants with infantile spasms conform strictly to this definition.

Age of onset

Infantile spasms are an age-specific disorder beginning in children during the first 2 years of life. It is unusual for infantile spasms to begin after 18 months, however. Most infantile spasms begin before 12 months of age, clustering between 4 and 7 months.

Types of spasms

Some seizures are characterized by brief head nods, whereas others consist of violent flexion of the trunk, arms, and legs. Infantile spasms can be classified into three major groups:17

  • Flexor spasms consist of flexion of the neck, trunk, arms, and legs. Spasms of the muscles of the upper limbs result either in adduction of the arms in a self-hugging motion or in abduction of the arms to either side of the head with the arms flexed at the elbow.
  • Extensor spasms consist of a predominance of extensor muscle contractions, producing abrupt extension of the neck and trunk, with extensor abduction or adduction of the arms, legs, or both.Mixed flexor-extensor spasms include flexion of the neck, trunk, and arms and extension of the legs, or flexion of the legs and extension of the arms with varying degrees of flexion of the neck and trunk.

Asymmetric spasms also occasionally occur. These consist of maintenance of a “fencing” posture.

Most patients have more than one seizure type.

Frequency of spasms

Infantile spasms frequently occur in clusters, and the intensity and frequency of the spasms in each cluster may increase to a peak before progressively decreasing. The seizures are very brief, so casual observers may miss single seizures. The number of seizures per cluster varies considerably, with some clusters consisting of as many as 150 seizures. The number of clusters per day also varies, with some patients having as many as 60 clusters per day.

Clusters occur rarely during sleep but frequently are seen shortly after awakening. Crying or irritability during or after a flurry of spasms is commonly observed. The number of infantile spasms occurring at night is similar to the number occurring during the day.

EEG patterns

Infantile spasms are associated with markedly abnormal EEGs. The most commonly found EEG pattern is hypsarrhythmia,18which consists of a high-voltage, slow record dominated by delta activity with frequent and multifocal spikes, sharp waves, and spike and slow wave complexes(Figure 1). Variations of hypsarrhythmia include:18


Electroencephalogram demonstrating hypsarrhythmia in an infant with infantile spasms. EKG = electrocardiogram.

  • hypsarrhythmia with interhemispheric synchrony
  • hypsarrhythmia with a consistent focus of abnormal discharge
  • hypsarrhythmia with episodes of attenuation
  • hypsarrhythmia consisting primarily of high-voltage slow activity with few sharp waves or spikes

During sleep, especially rapid-eye-movement (REM) sleep, a marked reduction or total disappearance of the hypsarrhythmic pattern may be noted. Although the hypsarrhythmic or modified hypsarrhythmic pattern is the most common type of interictal abnormality seen in infantile spasms, it is not seen in all patients who have this disorder.

Reviewed By: 
Steven C. Schachter, MD
Saturday, May 1, 2004