Neuromuscular junction disorder: edrophonium test and anticholinesterase treatment

What it is

Myasthenia gravis in the child is similar to adult autoimmune myasthenia and is due to binding of antibody to acetylcholine receptors on the post-junctional synaptic membrane, which gives a reduction of the number of functional receptors. It is the most common NMJ disorder, and the autoantibodies are to the postsynaptic ACh receptor.

The other neuromuscular junction disease set beside it is Lambert-Eaton myasthenic syndrome, which is uncommon. Its autoantibodies are to the presynaptic Ca2+ channel with decreased ACh release, it gives proximal muscle weakness and autonomic symptoms of dry mouth and impotence, it improves with muscle use where myasthenia gravis worsens with muscle use, and it is associated with small cell lung cancer while myasthenia gravis is associated with thymoma and thymic hyperplasia.

How it presents

Ophthalmoplegia, ptosis, loss of facial expression and difficulty chewing, with generalised proximal weakness. The muscle fatigues, so the weakness is worse at the end of the day.

Bilateral ptosis, diplopia and progressive weakness worse at the end of the day, with reactive pupils and a dysphagia and change in voice noticed recently, is the picture described in a middle aged male. Nasal voice, ptosis and dysphagia with respiratory acidosis is what brings the patient to hospital.