Module 3.3.2 (Management of Myasthenia Gravis)

Question 1

What are the signs and symptoms of MG?

Answer 1

Muscle weakness

• Extraocular, bulbar or proximal limb muscles
• Droopy eyelids (ptosis) or double vision most common
• Difficulty in swallowing, slurred or nasal speech, difficulty chewing, and facial, neck, respiratory muscle, and extremity weakness

Fatigue

Pain, secondary to muscle ache or cramps

Symptoms may worsen with

• Extreme heat or emotional stress, infection, systemic illness, pregnancy, the menstrual cycle, or drugs that affect neuromuscular transmission

Question 2

How to diagnose MG? Provide FIVE ways.

Answer 2

Ach-R antibodies

• +ve in approx 85% of patients
• if -ve, consider testing for MuSK antibodies

​Neurophysical tests

• Repetitive stimulation or positive single-fiber electromyography

TFTs and vitamin B12 concentrations

• Patients with MG are at higher risk of other autoimmune disorders

CT chest –< to check for thymoma (tumour on thymus gland)

Brain MRI if the patient has ocular signs only and serology -ve

Investigations unclear or -ve but MG is still suspected, consider edrophonium (tensilon) test.

Question 3

What is the treatment for patients with a thymoma?

Answer 3

Thymectomy –> surgery to remove thymus gland

Question 4

Why are acetylcholinesterase inhibitors used in the treatment of MG? What is used as 1st line treatment and how is it used? What to use to treat side effects?

Answer 4

To treat symptoms of MuSK -ve mild generalised myasthenia gravis or ocular myasthenia

• Pyridostigmine 1st line –> 30-45 mins before eating
• Time doses for when the patient is most fatigued
• Use the lowest effective dose

Use anticholinergic to treat muscarinic side effects (e.g. diarrhoea, abdominal pain, cramps).

> SR pyridostigmine can be usedful overnight -180mg at night

> Neostigmine (IV) in intensive care setting

Question 5

Why is immunosuppression used in the treatment of MG? What are the treatment options?

Answer 5

• Addresses underlying autoimmune disease

For moderate to severe myasthenia gravis OR if the response to pyridostigmine incomplete after 4-6 weeks (when remission achieved, slowly discontinue pyridostigmine, symptomatic treatment no longer required)

Treatment options

• Prednisolone (reduce the dose gradually after 4-6 weeks, according to response and tolerability)

PLUS

• Azathioprine
• Mycophenolate mofetil
• Mycophenolate sodium
• Methotrexate

Question 6

For MG Treatment, what to use for a myasthenic crisis, pre-operatively, for pregnant women, for severe treatment-resistant disease?

Answer 6

• IV immunoglobulin or plasma exchange–> myasthenic crisis or pre-operatively

> IV immunoglobulin may also be used in pregnancy, severe treatment-resistant disease, intolerance to other treatments

Question 7

What to use in refractory disease for MG?

Answer 7

Ciclosporin, rituximab or cyclophosphamide

Question 8

What is the treatment to use in MuSK +ve myasthenia gravis?

Answer 8

Plasma exchange or rituximab

Question 9

What are some drugs to avoid or use with caution in myasthenia gravis?

Answer 9

Avoid

• D-penicillamine
• Botulinum toxin type A
• Interferon alfa

Use with caution

• Neuromuscular blocking drugs: IV lignocaine in large doses
• Aminoglycosides
• Fluoroquinolones
• Macrolides