Paediatrics: Neuromuscular disorders

Neuromuscular disorders

See also the floppy infant. In children with neuromuscular problems, first think about the anatomical site that is affected (Fig. 14.7).

·  Brain.

·  Spine.

·  Anterior horn cell.

·  Peripheral nerve.

·  Neuromuscular junction.

·  Muscle.

Cerebral insult

Any brain insult may make a child unreactive and move less. In these child-ren there may be obvious signs of cerebral dysfunction such as enceph-alopathy. Facial movement and peripheral power are good if the child is able to follow commands. However, they may have low tone in the trunk, with relatively better tone at limb extremities. Good examples are Down or Prader-Willi syndromes. Reflexes should be present. If there is damage to the upper motor neuron then there will be spasticity with increased tone and brisk reflexes, e.g. cerebral palsy.

Spinal cord lesions

Spinal tumours and transverse myelitis should produce a rough level, beneath which there will be upper motor neuron signs or a sensory level or both. Spinal cord tumours are normally associated with a number of signs including constipation and urinary symptoms. There are particular signs which should always be investigated.

When to worry about a spinal cord lesion

·  Neurological signs, particularly when objective, e.g. hypereflexia and paresis, at a level beneath C1

·  Back pain with no other signs in children under 11yrs

·  Change in urinary function or bowel habit with back pain in older children

Transverse myelitis

Quick onset (i.e. in days and sometimes hours) of weakness, and/or anaes-thesia, and/or urinary dysfunction, and/or bowel disturbance, often within a week of a minor viral infection. It may be associated with back pain. Although later on there will be upper motor neuron signs, where there is an acute presentation, there may be reduced reflexes and power for the first days. However, where the weakness continues there will be a gradual increase in the reflexes and tone. Urgent imaging of the cord by spinal MRI with gadolinium  required to exclude cord compression, and in many cases will confirm appearances of myelitis.

Management

·Immediate admission for monitoring of respiratory status. Review for urinary and GI disturbance. Feeding/swallowing assessment.

·Early introduction of physiotherapy and occupational therapy to avoid joint contracture.

·Control of pain.

Methylprednisolone: IV treatment (30mg/kg, given over a period of at least 30min for 3 days) normally used initially, if no response consider other immune-modulatory therapy.

Anterior horn cell disorders

Disorder here produces flaccid, areflexic limb, normally sparing the face. 

Polio

·  Now rare. May still be seen following vaccination, or in immigrants.

·  Long-term, the limb becomes flaccid and wasted.

Spinal muscular atrophies

Confirmation of these conditions includes fibrillation on EMG and homozygous deletion of survival motor neuron (SMN) gene.

·  Type 0 (neonatal form): very severe, often with arthrogryposis.

·  Type 1 (Werdnig–Hoffman): severe with onset in the first months of life. Typically, there are ‘bright eyes’, severe hypotonia, ‘frog-like posture’, areflexia, and weakness that is present more in the legs than arms. Normally fatal by 2yrs of age.

·  Type 2: onset in the first years of life with low tone, peripheral weakness, absent reflexes, and scoliosis.

·  Type 3: adolescent onset with progressive weakness and gait disturbance, loss of reflexes, and low tone.

These disorders will have similar DNA results, so do not make a prognosis on the basis of the DNA result. They are very complicated, and will need to be reviewed by specialists, with reference to:

·  An accurate prognosis based on clinical assessment.

·  Advice on appropriate therapies e.g. invasive ventilation for type 1.

Multidisciplinary support for occupational, physio and speech therapies, as well as dietary, respiratory, neurological, psychological and social support.