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Definition of the cerebral palsies

Many definitions of the term CP have been proposed in an attempt to define a condition in which the causes, mechanisms, presenting patterns of the

disorder and brain lesions are multiple. The most recent and comprehensive definition was proposed by Mutch and colleagues (1992) who describe the condition as

"an umbrella term covering a group of non-progressive, but often changing, motor impairment syndromes secondary to lesions or anomalies of the brain arising in the early stages of its development".

Although many clinicians and researchers are in agreement as to the

definition of CP, there is considerable debate as to how the disorder should be classified. The reason for this is in part historical as the condition was thought to consist of a relatively homogenous group of children whose

neurological dysfunction was caused mainly by perinatal factors such as birth asphyxia. However, in recent years it has become apparent that children diagnosed as having cerebral palsy are in fact a highly heterogenous group of mixed aetiology.

Types of cerebral palsv

In describing the cerebral palsies it is necessary to discuss both the type of motor disorder and its distribution. It is important to consider that there is variability in both the type and the severity of CP.

The distribution of the motor disorder is commonly divided into 3 main groups (Hagberg et al 1989);

/or

■ quadriplegia an d W rap leg ia ■ diplegia and

■ hemiplegia.

The terms paraplegia, monoplegia and triplegia are also used occasionally but are thought to occur rarely in CP.

The terms quadriplegia and tetraplegia are sometimes used interchangeably and imply that all four limbs are affected but that the upper limbs may be slightly more involved. Diplegia implies that all four limbs are affected with the lower limbs more involved than the upper limbs. In hemiplegia only one side of the body, either the left or right is affected.

Three main types of motor disorder are commonly described; ■ spasticity

■ ataxia and

■ dyskinesia or athetosis

topography.

In many instances the type of CP is mixed, for example spasticity and athetosis, although one type may predominate.

S p asticity usually presents a picture of muscle stiffness and fixed posture with a limited range of movement and direction. The voluntary motor patterns are stereotypic with a paucity of movement being obvious. The degree of spasticity varies with the child's condition; for example the child's emotional state, whether they are excited or frightened, may alter the degree of

spasticity.

A thetosis is characterised by the presence of abnormal movements or postures, the child often appears unsteady. The coordination of movement and regulation of muscle tone are affected and bizarre and purposeless movements appear to interfere with voluntary activity. The movements may be slow and writhing or fast, jerky and irregular.

A taxia is characterised by muscular incoordination with poor balance, a staggering gait and general unsteadiness. Tremor may be present.

On the basis of the above description the classification system appears relatively straight forward, however the nature of CP is not. It is rare to find pure forms of athetosis or spasticity, although the condition is nonprogressive, the physical symptoms are known to change over time thus affecting the way

in which a child will be classified. The exact nature of the disability may only become clear when particular motor milestones are reached.

Aetiology of the cerebral palsies

Aetiological factors are commonly divided into three groups: • pre-natal

• peri-natal and

• postnatal events (Bax 1964, Crothers and Paine 1988).

Although there has been a long held belief that birth asphyxia is one of the major causes of CP, this view is increasingly being questioned. Recent studies suggest that intrapartum insults may be responsible for less than 10% of cases of CP (Blair and Stanley 1988, Richard et al 1989). Bax (1989) suggests that the cause of CP probably remains unknown in approximately 80% of cases.

The main risk factors thought to be associated with CP are summarised in Table 4 and classified according to the aetiology and when the insult occurred; prenatal, perinatal or postnatal. The table is a collation of the results of many studies. Although there are numerous factors listed, the majority are confounded by prematurity which has been found to be the strongest single predictor (Stanley and Alberman 1984). Intracranial

haemorrhage in the preterm infant is of prognostic significance (Cooke 1990), however it is not at all clear what determines which infants sustain such

(Alexander et al 1991). Interestingly, Stanley et al (1987) found that whilst the risk of developing CP was greatest in the preterm infant, during the period of their study 90% of cases occurred in infants of greater than 30 weeks

gestation.

Table 4. The most commonly identified causes and risk factors associated

Aetiology

Risk factors

Prenatal

(accounts for the majority of causes of CP, although the exact aetiology in the many cases remains unknown) preterm birth intrauterine growth retardation brain malformations genetic factors

Maternal factors

Perinatal

(probably accounts for less than 10% of all cases).

• birth trauma asphyxia

Infant factors

polycythaemia hypoxic-ischaemic encephalopathy