Myasthenia Gravis

Question 1

Myasthenia gravis presentation

Answer 1

The patient has been suffering with double vision.Examine her cranial nerves.

Question 2

Clinical signs of Myasthenia gravis

Answer 2

1. Bilateral ptosis (worse on sustained upward gaze)
2. Complicated bilateral extra‐ocular muscle palsies
3. Myasthenic snarl (on attempting to smile)
4. Nasal speech, palatal weakness and poor swallow (bulbar involvement)
5. Demonstrate proximal muscle weakness in the upper limbs and fatiguability. The reflexes are normal
6. Look for sternotomy scars (thymectomy)
7. State that you would like to assess respiratory muscle function (FVC).

Question 3

Associations of Myasthenia gravis

Answer 3

• Other autoimmune diseases, e.g. diabetes mellitus, rheumatoid arthritis, thyrotoxicosis, SLE and
• Thymomas

Question 4

Cause of Myasthenia gravis

Answer 4

Anti‐nicotinic acetylcholine receptor (anti‐AChR) antibodies affect motor end‐plate neurotransmission

Question 5

Investigations of Myasthenia gravis

Answer 5

Diagnostic tests:
1. Anti‐AChR antibodies positive in 90% of cases
2. Anti‐MuSK (muscle‐specific kinase) antibodies often positive if anti‐AChR negative
3. EMG: decremented response to a titanic train of impulses
4. Edrophonium (Tensilon) test: an acetylcholine esterase inhibitor increases the concentration of ACh at the motor end plate and hence improves the muscle weakness. Can cause heart block and even asystole.
Other tests
1. CT or MRI of the mediastinum (thymoma in 10%)
2. TFTs (Grave’s present in 5%)

Question 6

Treatments of Myasthenia gravis

Answer 6

Acute
* IV immunoglobulin or plasmapheresis (if severe)

Chronic
1. Acetylcholine esterase inhibitor, e.g. pyridostigmine
2. Immunosuppression: steroids and azathioprine
3. Thymectomy is beneficial even if the patient does not have a thymoma (usually young females)

Question 7

Lambert–Eaton myasthenic syndrome (LEMS)

Answer 7

1. Can be paraneoplastic , e.g. SCLC or Autoimmune.
2. Antibodies to voltage-gated Ca2+ channels on pre-synaptic membrane
3. Diminished reflexes that improve after exercise
4. Lower limb girdle weakness and gait difficulty (unlike myasthenia gravis)
5. Autonomic involvement (Dry mouth, constipation, impotence)
6. EMG shows a ‘second wind’ phenomenon on repetitive stimulation

Question 8

Causes of bilateral extra‐ocular palsies

Answer 8

1. Myasthenia gravis
2. Graves’ disease
3. Mitochondrial cytopathies, e.g. Kearns–Sayre syndrome
4. Miller–Fisher variant of Guillain–Barré syndrome
5. Cavernous sinus pathology

Question 9

Causes of bilateral ptosis

Answer 9

1. Congenital
2. Senile
3. Myasthenia gravis
4. Myotonic dystrophy
5. Mitochondrial cytopathies, e.g. Kearns–Sayre syndrome
6. Bilateral Horner’s syndrome

Question 10

Causes of bilateral Horner’s Syndrome

Answer 10

• Hereditary sensory autonomic neuropathy type III
• Amyloidosis
• DM
• Multiple system atrophy
• Pure autonomic failure
• Spinal artery thrombosis
• Bilateral cervical sympathectomy