Immunology

Question 1

What are examples of some autoimmune diseases?

Answer 1

Rheumatoid arthritis
Myasthenia Gravis
Scleroderma
Polymyositis
Vasculitis
Dermatomyositis
Lupus
Sjogren’s Syndrome
Relapsing polychondritis
Eosinophilic fasciitis

Question 2

What is myasthenia Gravis?

Answer 2

an autoimmune condition that causes muscle weakness that gets progressively worse with activity and improves with rest.

Question 3

Who is affected by myasthenia gravis?

Answer 3

Females under 40 years old
Males over 60 years old
There are strong links between thymomas and MG

Question 4

What is the pathophysiology of MG?

Answer 4

1. Initiating event
2. Self-reactive B cells activated by nAchR subunits in secondary lymphoid tissues.
3. Plasma cell differentiation
4. Secretion of IgG antibodies that bind to nAchR
5. Decreased stimulation of nAchR by endogenous Ach
6. Decreased muscle contraction.
   Antigen (nAchR): Antibody (anti-nAchR IgG) complexes also trigger complement system activation.

Question 5

What is the clinical presentation of MG?

Answer 5

Symptoms vary between patients (mild -> severe, life threatening)
- extraocular muscle weakness → double vision
- eyelid weakness → drooping of the eyelids
- weakness in facial movements
- difficulty with swallowing
- fatigue in the jaw when chewing
- slurred speech
- progressive weakness with repetitive movements.

Question 6

How is MG diagnosed?

Answer 6

• Laboratory tests
  
  • Anti-AChR antibodies (85%)
  • Anti-MuSK antibodies (10%)
  • Anti-LRP4 antibodies (<5%)
• scan the thymus gland - look for a thymoma
• Repetitive nerve stimulation - gradually reducing responses (smaller and smaller muscle response with each repetitive stimulus) indicates NMJ dysfunction
• Edrophonium test

Question 7

How is MG treated?

Answer 7

• Increase neurotransmission (to improve symptoms) - first line drugs for mild/moderate MG - reversible anti-cholinesterase agents e.g., pyridostigmine
• Surgery (if indicated) - thymectomy
• Immunosuppressants (to reduce autoimmune reactions) - second line treatments for moderate/severe MG - such as corticosteroids, azathioprine, rituximab
• MG crisis - O2 and/or ventilator, plasmapheresis or IVIG