Myasthenia gravis

Question 1

Myasthenia gravis definition

Answer 1

• autoimmune disorder
• insufficient working acetylcholine receptors

Question 2

Myasthenia gravis presentation

Answer 2

• muscle fatiguability
• progressive weakness when exercising
• improves on rest
• extraocular weakness - diplopia
• proximal weakness - face, neck, limb girdle
• ptosis and dysphagia

Question 3

Myasthenia gravis differentials

Answer 3

• multiple sclerosis
• motor neurone disease
• stroke
• Lambert Eaton syndrome
• (if ocular symptoms) Horner’s

Question 4

Myasthenia gravis investigations

Answer 4

• single fibre electromyography - high sensitivity
• repetitive nerve stimulation
• autoantibodies - to Acetylcholine, anti-muscle-specific tyrosine kinase
• ice test - ice on eyes, ptosis improves after 3 minutes
• CT thorax to exclude thyoma

Question 5

Myasthenia gravis management

Answer 5

• acetylcholinesterase inhibitors, e.g. pyridostigmine
• immunosuppression (initially prednisolone), e.g. steroids, azathioprine, cyclosporine
• (during crisis) plasma exchange, IVIG
• thymectomy to treat thyoma