Myasthenia gravis

Question 1

Myasthenia gravis

Answer 1

an acquired autoimmune disorder

• twice more common in women than men
• peak age of incidence around 30
• strong association with other autoimmune conditions

Question 2

pathophys

Answer 2

• antibodies are produced against postsynaptic acetylcholine receptor
• impair neuromuscular transmission
• failure to trigger muscle action potential
• this causes fatigability

Question 3

clinical features

Answer 3

1. hyperplasia of thymus gland
2. fatigable + painless muscle weakness - worse later on the day and on exertion
3. Fatigable ptosis and diplopia
4. Facial and Bulbar muscles - Dysphagia and Dysarthia

Question 4

Investigation

Answer 4

1. Anti acetylcholine receptor antibodies are present in 80-90% of cases
   - are diagnostic
2. Nerve conduction studies and EMG
   - repetitive nerve stimulation : a characteristic reduction in nerve response is seen
3. Chest CT - underlying thymoma
4. Tensilon test - Intravenous bolus of IV Endrophonium is positive and shows instant improvement from weakness

Question 5

Management

Answer 5

1. First line;
   Oral Anticholinesterases-Pyredostigmine

• stop acetylcholine from being broken down
• increase the level and duration of its action
• help but do not alter its natural history

2. Immunosuppressant
   - Oral steroid -> Prednisolone
   - Azathioprine

• used by patients who do not respond to Pyridostigmine