Paediatrics: Muscular disorders

Muscular disorders

Muscular dystrophies

Are a group of congenital disorders that are characterized by dystrophic change on muscle biopsy. They can affect muscles in different patterns and are characteristically associated with a raised creatine kinase enzyme.

Duchenne muscular dystrophy (DMD)

This condition classically presents within the first 4yrs with delayed motor milestones and mild speech delay. DMD is an X-linked recessive condition that lies at the severe end of the spectrum of disorders and is due to a molecular abnormality of dystrophin.

Examination

·  Waddling lordotic gait.

·  Calf hypertrophy.

·  Weakness in limb girdles (lower more than upper): Gower’s sign.

·  Sparing of the facial, extra-ocular, and bulbar muscles.

Investigation

·  Markedly raised creatine kinase.

·  Genetic analysis: this does not differentiate between the milder Becker muscular dystrophy (BMD) and more severe DMD, therefore expert interpretation is required.

·  Outpatient management of NMJ and muscular disorders.

Myotonic dystrophy

Autosomal dominant disorder with expand-ed CTG trinucleotide repeats on chromosome 19 (and anticipation when transmitted from mother).

·  Congenital form: severe cases may present in the neonatal period and are almost always of maternal inheritance. Infants present with hypotonia, feeding difficulty, tent-shaped mouth, and respiratory impairment. Treatment is supportive, but, notably, the symptoms become less disruptive as the child grows.

·  Later onset form: children present with hypotonia, myopathic face, and global developmental delay. Later complications include diabetes mellitus, cataracts, and cardiac involvement. The diagnosis will initially be made by the characteristic clinical picture.

Diagnosis

Confirmation can be made on examination of both parents and DNA analysis. EMG demonstrates the characteristic myotonic discharges, but is not needed for diagnosis.

Management

See  Management  of  neuromuscular  junction  and  muscular  disorders.

Caution There is a particular risk of malignant hyperthermia during general anaesthesia.

Congenital myopathies

These are a group of mainly autosomal recessive disorders characterized by:

·muscle weakness;

·hypotonia;

·variable involvement of the facial, bulbar, and extra-ocular muscles.

The congenital myopathies can be associated with arthrogryposis and if present in the neonate, may improve with good management for the first years.

Diagnosis

·Clinical picture.

·EMG and nerve conduction studies.

·DNA analysis.

·Muscle biopsy is used when the commoner disorders (myotonic dystrophy, DMD, and spinal muscular atrophy) have been excluded.