Neuromuscular Junction Disorders

Question 1

What is the underlying pathology of Myasthenia Gravis (MG)?

Answer 1

Generatio of IgG autoantibodies to ACh receptor on post-synaptic membrane of motor end plates
Blocks synaptic transmission at NMJ

Question 2

What is a thymoma?

Answer 2

Tumour of epithelial cells of thyroid

25% of MG sufferers have a thymoma

Question 3

How does MG present?

Answer 3

Weakness/fatigability that gets worse throughout day
Fluctuating proximal weakness (mostly upper limb)
Symmetrical diplopia/ptosis
Dysphagia
Speech difficulties
Wasting/resp difficulties
Tendon reflexes preserved

Question 4

What are the appropriate investigations in suspected MG?

Answer 4

Serum anti-AChR antibody titre (90%)
Single fibre electromyography (decreased response)
TFTs/CT (thymoma)
Edrophonium/Tensilon test

Question 5

What is the management of MG?

Answer 5

Avoid aminoglycosides
Lifelong long-acting oral anticholinesterases (Neostigmine/Pyridostigmine)
Corticosteroids for relapses (Azathioprine for steroid/sparing)
Thymectomy

Question 6

What is the prognosis of MG?

Answer 6

May never progress beyond opthalmoplegia
Periods of remission up to 3yrs may occur
Outlook poor if resp muscle involvelment