Myasthenia gravis

Question 1

What group of patients does MG occur in?

Answer 1

Women under 40

Men over 60

Question 2

What are the features of MG?

Answer 2

A neuromuscular disorder

Muscle weakness that gets progressively worse on activity and improves with rest
Symptoms minimal in morning and get worse during day

Mostly affects proximal muscles and small muscles in head and neck leading to:
Diplopia - due to extra ocular muscle weakness
Ptosis
Weakness in facial movements
Difficulty with swallowing
Fatigue in jaw when chewing
Dysarthria
Progressive weakness with repetitive movements

Question 3

What conditions is MG also associated with?

Answer 3

Thymomas in 10-20% of MG patients
Autoimmune disorders - pernicious anaemia, autoimmune thyroid disorders, RA, SLE
Thymic hyperplasia

Question 4

What investigations are carried out in MG?

Answer 4

1st line = Test for acetylcholine receptor antibodies/MuSK antibodies/ LRP4 antibodies

If antibody test -ve:
Perform repetitive nerve stimulation +/- single fibre electromyography

CT thorax:
Only if MG confirmed by above test
To exclude thymoma

MRI:
To exclude brain pathology

Tensilon test:
IV edrophonium injection which reduces muscle weakness temporarily
Not commonly used due to risk of cardiac arrhythmias

Question 5

What is the management for MG?

Answer 5

1st line = pyridostigmine (long-acting acetylcholinesterase inhibitor)

Immunosuppression may be used:
Initially prednisolone
Azathioprine, cyclosporine, mycophenolate mofetil

Thymectomy

Question 6

What is myasthenic crisis?

Answer 6

A severe complication of myasthenia gravis
Can be life threatening
Causes an acute worsening of symptoms
Triggered by another illness such as respiratory infection
Can lead to respiratory failure due to weakness in muscles of respiration

Question 7

What is the management for myasthenic crisis?

Answer 7

IV immunoglobulins

Plasma exchange