Myasthenia Gravis

Question 1

Is an autoimmune disorder where antibodies are produced to what receptors?

Answer 1

Acetylcholine receptors.

Question 2

MG is more common in men or women?

Answer 2

women (2:1)

Question 3

What are some features of MG?

Answer 3

• Muscle fatigability (key feature)- weaker during periods of activity and slowly improve after periods of rest.
• Other features
  
  • Extraocular muscle weakness: diplopia
  • Proximal muscle weakness: face, neck, limb girdle.
  • Ptosis
  • Dysphagia

Question 4

What muscles are more commonly effected in MG?

Upper or lower limb

Answer 4

Upper limb muscles

But lower can still be effected.

Question 5

What muscles of the upper limbs are more likely to be effected?

Answer 5

Triceps, Wrist extensors and deltoids.

Question 6

What muscles of the lower limbs are more likely to be effected?

Answer 6

Quads, Hams and Hip Flexors.

Question 7

What conditions is MG associated with?

Answer 7

• Thymic hyperplasia in 50-70%
• Autoimmune disorders: pernicious anaemia, autoimmune thyroid disorders, rheumatoid, SLE
• Thymomas in 15%

Question 8

How do you manage MG?

Answer 8

1. Immunosuppression: Prednisolone initially
2. Long-acting anticholinersterase (e.g. pyridostigmine)
3. Thymectomy

Question 9

How do you manage a myastheic crisis?

Answer 9

1. Plasmapheresis
2. IV Immunoglobulins

Question 10

How do you investigate for MG and what would you see?

Answer 10

• Single fibre electromyography: high sensitivity (92-100%)
• CT thorax to exclude thymoma
• CK normal
• Autoantibodies: around 85-90% of patients have antibodies to acetylcholine receptors. In the remaining patients, about about 40% are positive for anti-muscle-specific tyrosine kinase antibodies
• Tensilon test: not commonly used anymore due to the risk of cardiac arrhythmia