Infantile spasms constitute a unique and very serious epilepsy syndrome confined to infants. The usual characteristic features of this syndrome are:

  • tonic or myoclonic seizures
  • hypsarrhythmic EEGs
  • mental retardation

This triad is referred to as West's syndrome. (Not all cases of infantile spasms conform strictly to this definition, however.) Other names used in the literature include:

  • massive spasms
  • salaam seizures
  • flexion spasms
  • jackknife seizures
  • massive myoclonic jerks
  • infantile myoclonic seizures
  • Blitz-Nick-Saalam Krampfe (in the German literature)

Infantile spasms are an age-specific disorder beginning during the first 2 years of life. The peak age of onset is between 4 and 6 months. Approximately 90% of infantile spasms begin before 12 months of age.39 It is rare for infantile spasms to begin during the first 2 weeks of life or after 18 months.

Infantile spasms may vary considerably in their clinical manifestations. Some seizures are characterized by brief head nods, whereas other seizures consist of violent flexion of the trunk, arms, and legs. Most patients have more than one seizure type. Infantile spasms can be classified into three major groups:40

  • Flexor: flexion of the neck, trunk, arms, and legs. Spasms of the muscles of the upper limbs result in either adduction of the arms or a self-hugging motion, or adduction of the arms to either side of the head with the arms flexed at the elbow.
  • Extensor: a predominance of extensor muscle contractions, which produce abrupt extension of the neck and trunk, along with extensor abduction or adduction of the arms, legs, or both.
  • Mixed flexor-extensor: 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 occasionally occur, in which the infant maintains a "fencing" posture.

Infantile spasms may also be associated with autonomic dysfunction characterized by:

  • pallor
  • flushing
  • sweating
  • pupillary dilatation
  • lacrimation
  • changes in respiratory and heart rate41,42

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, and the casual observer may miss single seizures. The number of seizures per cluster varies considerably. Some clusters have as many as 150 seizures. The number of clusters per day also varies. Some patients have as many as 60 clusters per day. Clusters can occur during sleep or shortly after awakening. Crying or irritability during or after a flurry of spasms is commonly observed. The number of infantile spasms that occurs at night is similar to the number that occurs during the day.41

Infantile spasms are frequently associated with developmental delay. In a review of the literature, Lacy and Penry41 reported that only 10% of patients were developmentally normal at the time their infantile spasms were diagnosed. Patients whose symptomatic infantile spasms have identifiable causes have a higher incidence of retardation than patients whose spasms have idiopathic causes.42

Abnormal neurologic findings on physical examination are also commonly reported. Lacy and Penry42 reported that 70% of patients with infantile spasms have abnormal findings on neurologic examination. Children with identifiable etiologies for the spasms are much more likely to have neurologic impairment than those in the idiopathic group.42,43


Infantile spasms are usually associated with markedly abnormal EEGs. The most common interictal abnormality is hypsarrhythmia (See EEG).41,44-46 There are several variations:47

  • 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 
infant hypsarrhythmia EEG


infant hypsarrhythmia EEG

Example of hypsarrhythmia in an infant with infantile spasms. There are multifocal spikes and sharp waves. In addition, brief periods of suppression are noted. (Calibration 50 microvolts and 1 sec.)

During sleep (especially REM sleep) the hypsarrhythmic pattern may be markedly reduced or totally disappear.47 Some patients with infantile spasms do not show a hypsarrhythmic pattern.44 Some do not have hypsarrhythmia early in the course of the disorder but go on to develop the pattern.

Although hypsarrhythmia is associated primarily with infantile spasms, it occurs in other disorders as well.48

The ictal EEG changes during infantile spasms vary.40,50 Kellaway and colleagues40 found 11 different types of ictal EEG patterns, but 72% of seizures have shown a marked generalized attenuation of electrical activity.45,49 Ictal EEG abnormalities and clinical seizure type are not closely correlated.

Adapted from: Holmes GL. Classification of seizures and the epilepsies. In: Schachter SC, Schomer DL, eds. The comprehensive evaluation and treatment of epilepsy. San Diego, CA: Academic Press; 1997. p. 1-36.
With permission from Elsevier (

Authored by: Gregory L. Holmes | MD on 1/2004