Neurophysiology of spasms

Abstract

Spasms are a form of epileptic seizure typical of infancy. From a clinical point of view, the child presents a flexor–extensor movement involving the trunk and limbs and lasting about 1 s. Although asymmetry can be present, the seizure involves both sides of the body.

The ictal discharge most frequently associated with spasms in West syndrome (WS) is a diffuse triphasic slow high-amplitude wave and less frequently a low-amplitude brief rapid rhythm. The origin of the spasm in WS and classification as either partial or generalized seizure are the subject of much discussion.

Factors supporting partial origin include: interictal electroencephalography (EEG) characterized by multifocal anomalies; high incidence of focal cortical lesions and remission of spasms following surgical removal of focal lesions. Factors supporting generalized origin are: clinical involvement of the entire body; mostly generalized ictal EEG pattern; existence of idiopathic cases and possibility of spasms immediately following a partial seizure like a particular form of secondary generalization. In our opinion, the categories of ‘partial’ and ‘generalized’ seizures are not applicable to spasms in WS. Sometimes the spasms in WS can be observed together with other types of partial or generalized seizures.

Polygraphic recordings have demonstrated that despite being clinically similar, each spasm is different from the other because of a variable sequence in muscular contraction.

These data support the peculiar nature of the spasm in WS that could be a subcortical phenomenon that requires a cortical trigger.

Introduction

Spasms are defined as epileptic seizures characterized by brief axial contraction, in flexion, extension or mixed, symmetric or asymmetric, lasting from a fraction of a second to 1–2 s.

This particular type of epileptic seizure is characteristically associated with West syndrome (WS) and has been the subject of many studies because it is often associated with psychomotor arrest or cognitive regression, and is frequently resistant to drug treatment.

Before discussing the neurophysiology of spasms in WS, it is necessary to make at least two preliminary considerations.

Spasms can be observed in WS patients with different types of brain lesion, unilateral, bilateral or diffuse, classified as ‘symptomatic’, as well as in patients with normal psychomotor development and without brain lesions, classified as ‘cryptogenic’ or ‘idiopathic’ [1], [2]. Therefore, spasms represent a unique manifestation observed in WS patients with very different etiologies and lesions.

Another element to consider is that spasms in WS are a type of age-related seizure, with onset usually in the first year of life, although late onset up to 7–8 years of age has been reported in rare cases [3]. There are no reports of spasms with onset after puberty. Therefore, spasms in WS are associated with a particular phase of brain development.