Myasthenia gravis

Question 1

Describe myasthenia gravis?

Answer 1

• Autoimmune disease
• Antibodies to nicotinic acetylcholine receptors on post-synaptic NMJ
• Both B and T cells are implcated

Question 2

Describe the presentation of myasthenia gravis?

Answer 2

• Slowly worsening or relapsing muscular fatigue
• Muscular groups affected in a specific order:
  
  • Bulbar -> face -> neck -> limb girdle -> trunk

Question 3

What are the bulbar muscles?

Answer 3

• Chewing
• Swallowing

Question 4

Name some of the clinical signs of Myasthenia gravis (MG)?

Answer 4

• Ptosis
• Diplopia
• Myasthenic snarl when smiling
• ‘Peek sign’ of orbicularis fatigability
• When counting to 50, the voice fades
• (reflexes normal)

Question 5

What is pictured here?

Answer 5

• Peek sign
  
  • Eyelids begin to separate after manual opposition to sustained closure

Question 6

What is pictured here?

Answer 6

Myasthenic snarl

Question 7

What are the symptoms of MG exacerbated by?

Answer 7

• Drugs
• Infection
• Pregnancy
• Hypokalaemia
• Change of climate, emotion, exercise

Question 8

What drugs can exacerbate the symptoms of MG?

Answer 8

• Opiates
• Quinine
• Gentamicin
• Beta-blockers

Question 9

Name some differentials for MG?

Answer 9

• SLE
• Polymyositis
• Takayasu’s arteritis

Question 10

What can MG be associated with?

Answer 10

• Auotimmune disease
  
  • especially RA and SLE
• More common in women, associated with thymic hyperplasia
• More common men, associated with thymic atrophy or thymic tumour

Question 11

Describe the diagnostic tests for MG?

Answer 11

• Antibodies
  
  • Raised Anti-AChR antibodies
    
    • If (-) look at MUSK antibodies
• EMG
  
  • Decremental muscle response to repeat nerve stimulation
• CT to exclude thyoma
• Other
  
  • Ptosis improves >2mm after ice application >2minutes

Question 12

Describe the treatment of MG?

Answer 12

• Anticholinesterase inhibitor eg Pyridostigimine
• Immunosuppression
  
  • Relapses: Prednisolone (reduce dose on remission)
  • or Azathioprine, ciclosporin, mycophenolate
• Thymectomy

Question 13

Describe Pyridostigimine?

Answer 13

• Anticholinesterase inhibitor
• SEs:
  
  • Miosis
  • Vomiting
  • Increased saliva, lacrimation and sweating

Question 14

Describe a myasthenic crisis?

Answer 14

• Life-threatening weakness of respiratory muscles during relapse
• Monitor forced vital capacity (FVC)
  
  • Vetilatory support
• Treat any potential trigger
  
  • (infection, medications)
• Treated with Plasmapheresis or IVIg

Question 15

Describe the use of Plasmapheresis in a myasthenic crisis?

Answer 15

Removes ACHR antibodies from the circulation

Question 16

Diagram of myasthenia gravis NMJ

Answer 16