Neurological disorders

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11 Neurological disorders

CEREBRAL PALSY (Spastic paralysis: spastic paresis; Little’s disease)

The term cerebral palsy embraces a number of clinical disorders, mostly arising in childhood, the feature common to all of which is that the primary lesion is in the brain. The incidence of these disorders is such that cerebral palsy constitutes a major social and educational problem.

Cause. There is no single cause. Any event that results in damage to the brain may be responsible. Thus the causes may be classified into three groups: pre-natal, natal, and post-natal. Pre-natal causes include congenital defective development of the nervous system, and erythroblastosis leading to icterus gravis in the child, with consequent damage to the basal nuclei (kernicterus). Natal causes include damage to the brain and intracranial bleeds from birth injury, and anoxaemia with consequent cerebral anoxia. Prematurity is believed to be an important factor. Post-natal causes include infections such as pertussis, encephalitis, and meningitis, head injuries, and, in later life, cerebrovascular accidents (stroke). In children it is not always easy to ascribe the fault in a given case, but probably the commonest causes are damage to the brain during difficult labour and cerebral anoxia during birth.

Types. A number of clinical types may be recognised, of which the most important are:

1 spastic paresis

Mixed types also occur.

SPASTIC PARESIS

Pathology. Part of the motor cortex of the brain is replaced by areas of gliosis. There is degeneration of the pyramidal tracts.

Clinical features. Usually within the first year it is noticed that the child has difficulty in controlling the movements of the affected limbs, and there is delay in sitting up, standing and walking. Commonly the upper and lower limbs of one side are affected (hemiplegia). Less often there is involvement of a single limb (monoplegia), of both lower limbs (paraplegia), or of all four limbs (tetraplegia ¹). The trunk and face muscles may also be affected. On examination the features that are found constantly are weakness, spasticity, and imperfect voluntary control of movement. Usually there is also deformity, and in some cases there may be mental deficiency, impaired vision, or deafness. These various features are best considered separately.

Weakness. There is no true paralysis, but there may be fairly marked weakness of muscles. The weakness seldom affects all the muscles of a limb equally; often there is marked muscle imbalance which may lead to deformity.

Spasticity. The muscles are ‘stiff’: they resist passive movement of the joints, but when steady pressure is applied for some time they slowly relax, allowing the joint to be moved. When the pressure is released the spasm immediately returns. The tendon reflexes are exaggerated and muscle clonus may be elicited.

Lack of voluntary control. This is a striking feature, especially in severe cases. When the patient attempts to move a single group of muscles, other groups contract at the same time.

Deformity. When spasm and muscle imbalance are pronounced they lead eventually to the development of fixed deformity. The stronger muscles hold the limb constantly in an unnatural position, and secondary adaptive changes take place in the muscles and periarticular tissues. The commonest deformities in the upper limb are flexion contracture of the elbow, pronation deformity of the forearm, flexion of the wrist, and adduction of the thumb. In the lower limb the common deformities are adduction of the hip, flexion of the knee, and equinus of the ankle.

Mental deficiency. Impairment of mental capacity is sometimes present, but usually intelligence is normal. Lack of control of the facial and speech muscles may suggest mental impairment when in fact none exists. It is important that the medical advisers be not misled in this respect. Defective vision and deafness may also retard the child’s progress.

The severity of the disability varies widely from case to case. In the mildest examples the child is able to lead a normal active life with very little handicap, whereas in the worst cases the patient is almost helpless.

Prognosis. Since an essential part of the brain is destroyed and cannot be replaced, complete cure is impossible. All that can be hoped for is improvement. To achieve even this requires endless patience on the part of the patient and the attendants. Yet perseverance is nearly always well rewarded, and there are few cases in which worth-while improvement cannot be gained. Thus a patient formerly dependent upon others in many daily activities may often gain independence, and many who were previously unable to work become capable of earning their own living.

Treatment. Up to the age of about 5 years treatment may be carried out at non-residential centres, but after the age of 5 a child who is considerably disabled should be admitted to a special residential school where adequate facilities and trained staff are available.

The methods of treatment available are muscle training, corrective splinting, speech therapy, and operations on tendons, bones, or nerves.

Muscle training. This is an important part of the management of all except the mildest cases, and it is best carried out by a physiotherapist with experience of this very demanding work. The principles of muscle training are to teach the child to relax spastic muscles, to develop the use of individual muscle groups, and to improve coordination. Repetitive rhythmic movements are valuable. Stage by stage the child is instructed in dressing, toilet, feeding, and walking.

Corrective splinting. Splints or plasters are especially useful in overcoming the deformities induced by spastic muscles. Deformity is first corrected by gradual stretching of the contracted muscles, if necessary under anaesthesia. The limb is held by plaster in the over-corrected position for 6–8 weeks. Thereafter removable braces or splints (orthoses) may be used indefinitely to prevent recurrence of the deformity.

Speech therapy. Many spastic children have a speech defect which, with constant grimacing and salivation, may lead one to suppose that there is mental deficiency when in fact this is not so. In these cases the speech therapist is sometimes able to achieve a marked improvement.

Operative treatment. Operations for spastic paralysis should be approached with caution: striking benefit may be achieved in appropriate cases, but injudicious operation in unsuitable cases has often led to disappointing results. Operation may be upon tendon, joint, or nerve.

Tendon division or elongation. Division or lengthening of the tendon of a spastic muscle reduces its mechanical advantage and improves muscle balance. Examples are lengthening of the calcaneal tendon in a case of spastic equinus deformity, and tenotomy of the adductors of the hip for adduction deformity.

Tendon transfer. At certain sites transfer of the insertion of a muscle that is aggravating deformity may so modify the muscle’s action that it acts beneficially instead of as a deforming force. An example is the transfer of the insertion of the hamstring tendons from the tibia to the back of the femoral condyles in a case of flexion deformity of the knee: this eliminates the undesirable action of the spastic hamstrings in flexing the knee, while enhancing their desirable action as hip extensors.

Arthrodesis. When skeletal growth is complete it is sometimes of benefit to fuse a joint in a position of function, to eliminate persistent deformity from the pull of spastic muscles. Thus a wrist that lies constantly flexed may be fused in a neutral or slightly extended position, with consequent improvement in function.

Osteotomies. Division of the bone to correct angular and rotational deformities may be of value especially in the lower limb.

Neurectomy. The principle is to divide part or the whole of a nerve that supplies an overacting spastic muscle. An example is division of the anterior branch of the obturator nerve to overcome spastic adduction at the hip.

ATHETOSIS

Pathology. The main damage is in the basal nuclei.

Clinical features. The principal feature is the occurrence of generalised overlaid involuntary movements which have no pattern and which interfere with the performance of normal movements. Any part or the whole of the muscular system may be affected.

In mild cases the child is able to lead a fairly normal life, but in the worst examples the patient may be unable to sit up, walk, feed himself, or express himself in words, even though the mental state may be good.

Treatment. The first essential in treatment is to teach the child general relaxation. Once this has been achieved, purposeful voluntary movements can be taught. Splints and appliances may be required, but in pure athetosis there is no place for operations on the limbs. In some cases of severe athetosis improvement has been reported after surgical ablation of the globus pallidus.

SPINA BIFIDA

The term spina bifida implies a failure of the enfolding of the nerve elements within the spinal canal during early development of the embryo. The defect varies in degree and in its site (Fig. 11.1). In the mildest cases there is no more than a failure of fusion of one or more of the vertebral arches posteriorly, in the lumbo-sacral region. This is often of no clinical significance. Less often, the posterior bony deficiency is marked on the surface by an abnormality of the overlying skin, in the form of a dimple, a tuft of hair, a lipomatous mass, or a dermal sinus. In these cases there may be an underlying abnormality involving nerves of the cauda equina. These relatively minor varieties of spina bifida, in which the defect is not obvious at the skin surface, are termed spina bifida occulta. This contrasts with spina bifida aperta, in which there is a major defect of enfolding of the nerve elements, involving not only the bony vertebral arches but also the overlying soft tissues and skin, and often the meningeal membranes enclosing the spinal canal, so that the neutral tube itself is exposed and open. This major variant of spina bifida may occur anywhere in the spine but is commonest in the thoraco-lumbar region, and it is attended by grave impairment of nerve function.

Fig. 11.1 Spina bifida. Diagrams showing four grades of severity of the posterior defect of the spinal canal. A Spina bifida occulta, B meningocele, C myelomeningocele, D rachischisis.

SPINA BIFIDA OCCULTA (Occult spinal dysraphism)

As noted above, the bony defect is simply a failure of fusion of the vertebral arches posteriorly (Fig. 11.1A). When there is neurological involvement the overlying skin nearly always shows an abnormality, as already described.

Impairment of nerve function may be caused in some such cases by tethering of the dura, and through this the spinal cord, to the skin surface by a fibrous membrane. Traction on the cord becomes gradually worse as the spinal column elongates disproportionately to the spinal cord: this can cause slow progression of the neurological deficit. A rather similar effect is caused by tethering of the distal end of the spinal cord by the filum terminale. Rarely, too, a bifid cord is transfixed by a delicate bar of bone crossing the spinal canal in the antero-posterior plane (diastematomyelia) with consequent tethering and progressive neurological impairment. In yet other cases the neurological fault may be a consequence of myelodysplasia, a congenital defect of development of nerve tissue.

In cases of occult spinal dysraphism there is no close correlation between the severity of the bony defect and the degree of neurological impairment. Often there is no neurological involvement; but on the other hand it may be severe. Clinically, the common manifestation of nerve involvement is muscle imbalance in the lower limbs, often with selective muscle wasting and deformity of the foot which often takes the form either of equino-varus or of cavus.

Investigation and treatment. The patient may be brought for advice because of an abnormality of the skin over the lumbo-sacral region, because of abnormality of the feet or perhaps just a limp, or because of urinary incontinence. A plain radiograph will show the extent of the bony deficiency.

If evidence of neurological impairment is lacking, treatment is not required. If neurological impairment or incontinence is present – and especially if there has been progressive deterioration – further investigations, including MR scanning and radiculography, are required. These may point to the presence of one of the structural lesions mentioned above, and in such a case neurosurgical intervention may be required: its object is to prevent further deterioration rather than to promote complete recovery.

SPINA BIFIDA APERTA (Overt spinal dysraphism; variations include rachischisis, myelomeningocele and meningocele)

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