Developmental problems and the child with special needs

Cerebral palsy

Cerebral palsy is a descriptive term which has been defined as ‘a group of permanent disorders of movement and posture causing activity limitation that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication and behaviour, by epilepsy, and by secondary musculoskeletal disorders’.

Children with cerebral palsy are not always hypertonic, but there are four main clinical types, some of which have well-described associations with underlying pathologies ( Table 5.2 ).

• 1.

  Spasticity : This is a velocity-dependent increase in tonic stretch receptors. Assessment of spasticity must be dynamic and is often described as feeling like a ‘clasp knife’.

• 2.

  Dystonia : This is spasm and sustained contraction of a muscle, leading to abnormal posturing. In time, it can lead to contractures. It is often described as feeling like ‘lead-pipe rigidity’.

• 3.

  Ataxia : Uncoordinated movements linked to a disturbed sense of balance and depth perception.

• 4.

  Choreo-athetoid : Hyperkinesia (excess of involuntary movements). These are often writhing in nature.

Children with cerebral palsy often have a mixed picture of movements, and this classification does not accurately describe how severely disabled the child is by their movement disorder. The Gross Motor Function Classification System (GMFCS) scale is useful as it describes the functional ability of a child's gross motor skills rather than focusing on the individual type of cerebral palsy.

Cerebral palsy can be mimicked by several other conditions and before making a firm diagnosis the differential diagnosis needs to be considered ( Table 5.3 ).

Particular care should be taken when there is a ‘family history’ of cerebral palsy to check that there is not an underlying inheritable cause. One must also ensure that a child who presents with ‘ataxic cerebral palsy’ does not have a treatable or definable underlying cause.

Management of cerebral palsy

Meeting the child and family's complex needs requires a multi-disciplinary team (see below). Here, we will describe some of the drugs and procedures which may be helpful.

Specific drug management of spasticity

Drugs used in the management of spasticity and their sites of action are shown in Figure 5.1 .

Diazepam : Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter regulating neuronal excitability in the nervous system. It has a direct effect on muscle tone. Diazepam is a GABA agonist. Due to its central location of action, it relieves spasticity and muscle spasms, but it has additional effects of sedation and acts as an anxiolytic. Long-term use can create dependency, but short-term use can be helpful for painful spasms (for example, after surgery), or to break cycles of distress and increasing spasticity.

Baclofen : Baclofen is also a GABA agonist and inhibits neuronal transmission at a spinal level. Its main adverse effect is sedation, which often limits its use. Its passage into the CSF when given orally is poor and high doses are often needed. When used intrathecally, via a surgically implanted continuous-delivery pump, only a tiny fraction of the equivalent oral dose needs to be given. This allows greater efficacy with fewer adverse effects.

Tizanidine : Tizanidine is an alpha-2 adrenergic receptor agonist and acts at the spinal level to help relieve spasms. It is particularly useful in children who are severely disabled by cerebral palsy and in those with night-time spasms, as it commonly has a sedative effect.

Botulinum toxin A : Botulinum toxin A works by chemically denervating the muscle, allowing the muscle to relax and thus improving function and cosmesis in some cases. It works by cleaving synaptosomal-associated protein (SNAP-25), which is a cytoplasmic protein which aids in the process of attaching the synaptic vesicle to the pre-synaptic membrane. This then stops the release of acetylcholine at the synapse and blocks neurotransmission. The effects gradually wear off (over about 3–6 months) as the myelin sheath retracts and new terminals are made, which form contacts with the myocyte to resume neurotransmission.

Dantrolene : Dantrolene works on spasticity and spasms by affecting the calcium uptake into skeletal muscles and decreasing the free intracellular calcium concentration. Sedation is less of a problem with dantrolene than with the other drugs mentioned, but it should be used cautiously as it can cause hepatic dysfunction and blood dyscrasias.

Other treatment for spasticity

Selective dorsal rhizotomy (SDR) : There has been renewed interest in the use of selective dorsal rhizotomy to treat spasticity, particularly in the more mobile groups of children with cerebral palsy (GMFCS levels 2 to 3). This surgical procedure divides some of the lumbar sensory nerve roots, thus interrupting the sensory–motor reflex arc responsible for increased muscle tone. Pre-operative assessment must include bladder assessment due to the risk of affecting continence, and children and families must be counselled about the risks. The child's general level of gross motor function is unlikely to change significantly, but there may be improvements in quality of gait together with improved comfort and ability to tolerate splints and postural management programme.

Question 5.4

The hypotonic (floppy) infant

A male infant is born at term but develops unexpected respiratory distress in the first few hours of life. He is admitted to the neonatal intensive care unit and started on antibiotics. Upon examination, he is noted to be hypotonic.

From the following list of possible anatomical locations (A–I), pick the area predominantly affected by pathology in each of the conditions (1–4) listed below:

• A.

  Anterior horn cell

• B.

  Cortex

• C.

  Cerebellum

• D.

  Muscle

• E.

  Neuromuscular junction

• F.

  Peripheral nerves

• G.

  Spinal cord

• H.

  Spinothalamic tract

• I.

  Unknown

• 1.

  Spinal muscular atrophy

• 2.

  Congenital myasthenia gravis

• 3.

  Down's syndrome

• 4.

  Congenital myotonic dystrophy

Answer 5.4

• 1.

  A. Anterior horn cell

• 2.

  E. Neuromuscular junction

• 3.

  I. Unknown

• 4.

  D. Muscle

See below for discussion.

Down's syndrome

Down's syndrome is caused by an additional copy of chromosome 21, either due to non-disjunction (most commonly), by a rearrangement of genetic material, called an unbalanced translocation, where extra genetic material associated with chromosome 21 is inherited, or by mosaicism (see Chapter 9 , Genetics).

Babies with Down's syndrome have typical dysmorphic features and are centrally hypotonic. They show delay in all of their developmental milestones and may have initial feeding difficulties. They may have associated congenital anomalies, including heart defects (present in up to 50% of infants). Children with Down's syndrome will have ongoing additional physical and learning needs throughout childhood and into adulthood.

Many newborn children with Down's syndrome have flaccid muscles and are described as ‘floppy’. In some children, this disappears as the child develops, but many remain in this ‘floppy’ state. There are a few follow-up studies of infants with Down's syndrome and it seems that this infantile floppiness does improve over time. There is a fairly widespread belief that the children remain with a degree of hypotonia and this state is often invoked as being responsible for much of their delay in motor milestones and impaired motor function.

However, this is controversial since there is no proper agreement as to either the exact cause or the definition of hypotonia and there is no consensus as to how to measure it. Some recent studies have shown that the hypotonia seen when children and adults with Down's syndrome are not moving (i.e. their tendency to have more ‘floppy’ muscles at rest) does not actually impair coordinated movement. The fact that the muscles are floppy at rest suggests there may be some peripheral component to the observed hypotonia.

Prader–Willi syndrome

Prader–Willi syndrome is caused by a deletion on the long arm of the paternally inherited chromosome (15q13) in 70% of cases, or due to maternal uni­parental disomy (25%). The remaining 5% are due to an imprinting defect, and only this form carries an increased risk for future pregnancy.

Prader–Willi syndrome should be considered in babies with feeding difficulties, those requiring nasogastric tube feeding, sticky saliva, extreme hypokinesia and a combination of central hypotonia and limb dystonia. Children with Prader–Willi syndrome also have distinctive facial characteristics and other dysmorphic features. Despite initial poor feeding, children with Prader–Willi syndrome begin to show increased appetite as they grow. This can lead to excessive eating (hyperphagia) and life-threatening obesity. They also have hypogonadism, causing immature development of sexual organs and delay in puberty. Learning disabilities can be severe. They tend to be particularly impaired in their emotional and social development.

Peroxisomal disorders

Peroxisomes are spherical organelles within cells containing important oxidative and other enzymes. Babies with peroxisomal disorders tend to present with extreme hypotonia of the neck in the context of general neonatal hypotonia.

Peroxisomal disorders can be divided into two categories:

• ‘Global’ peroxisomal disorders, where few or no peroxisomes are generated or where there are single peroxisomal enzyme defects that induce a similar phenotype.

• Adrenoleukodystrophy, which is an X-linked inherited condition, caused by a defect in the gene that codes for one of the ATP-binding transporters within the cell.

Measurement of very long chain fatty acids may detect some peroxisomal disorders, but there is no ‘metabolic screen’ which will detect all of them. Results must be correlated with clinical findings.

Particular clinical features which should be sought where a peroxisomal disorder is suspected in a hypotonic child include:

• Neonatal seizures

• Retinal blindness (Leber amaurosis)

• Sensorineural deafness

• Dysmorphic features of specific syndromes (e.g. Zellweger)

• Hepatomegaly

• Leukodystrophy

• Neuronal migration defects

Suspicion of a peroxisomal disorder should be present where a school-age boy shows developmental regression in the context of previously normal development (although there may be a number of other causes for this) and in older girls with spastic paraplegia.

Brain malformations

This category is very broad. There are many structural malformations within the brain which can lead to abnormal tone. One needs to ensure that the malformation is not caused by a metabolic disorder, which may require specific management.

Anterior horn cells

Nerve impulses generated in the anterior horn cells lead to activation of muscle fibres. Anterior horn cell disease usually leads to a specific pattern of weakness depending on the affected part. This is because medial cells innervate proximal muscles, whilst lateral cells innervate more distal muscle groups.

Disruption of anterior horn cells can lead to de­nervation, and the damaged alpha motor neurons produce spontaneous action potentials. These spikes cause the muscle fibres that are part of that neuron's motor unit to fire. This causes muscle twitches. We observe them as fasciculations. Reflexes are also lost.

As further degeneration occurs, only the remnants of the axon close to the muscle fibres remain. These individual axon fibres can also generate spontaneous action potentials; however, these will only cause individual muscle fibres to contract, resulting in fibrill­ation on electrophysiological testing (rarely performed nowadays).