Neurology - Myasthenia Gravis Flashcards
What is myasthenia gravis?
Autoimmune condition affecting the neuromuscular junction
Causing muscle weakness that worsens with activity and improves with rest
At what ages does myasthenia gravis typically affect men and women?
Women under 40
Men over 60
What is strongly linked to myasthenia gravis?
Thymomas
10-20% of patients with MG have a thymoma
30% of patients with a thymoma develop MG
What is the pathophysiology of MG?
Motor neurones communicate with muscles via the NMJ
ACh released from presynaptic membrane to post snyaptnic membrane causing contraction
In MG AChR bind to postsynaptic receptors blocking them and preventing stimulation
More use of muscles during activity, the more they get blocked
With rest symptoms resolve
What do AChR antibodies also do?
Activate complement system in the NMJ
Causing cell damage at the post synpatic membrane further worsening symptoms
What are the two other antibodies that can cause myasthenia gravis?
- Muscle-specific kinase (MuSK) antibodies
- Low-density lipoprotein receptor-related protein 4 (LRP4) antibodies
What are MuSK and LRP4?
Proteins needed for creation and organisation of the AChR
Destruction leads to inadequate AChRs
What is a critical feature of myasthenia gravis symptoms?
Weakness that worsens with muscle use and improves with rest
List common symptoms of myasthenia gravis.
- Difficulty climbing stairs
- Diplopia
- Ptosis
- Weakness in facial movements
- Difficulty with swallowing
- Fatigue in the jaw when chewing
- Slurred speech
How can fatiguability in the muscles be elicited?
- Repeated blinking exacerbates ptosis
- Prolonged upward gazing exacerbates diplopia
- Repeated abduction of one arm will result in unilateral weakness
What are some further examination steps are there for myasthenia gravis?
Checking for thymectomy scar
Testing FVC
What investigations are used for myasthenia gravis?
Antibody tests
CT or MRI of thymus
Edrophonium test
What antibodies are tested for in myasthenia gravis?
- AChR antibodies (around 85%)
- MuSK antibodies (less than 10%)
- LRP4 antibodies (less than 5%)
What is the edrophonium test?
Patients given edrophonium chloride (neostigmine)
Neostigmine blocks cholinesterase enzymes causing raised ACh at the NMJ
Relives weakness
Positive result suggests MG
What are the treatment options for myasthenia gravis?
- Pyridostigmine
- Immunosuppression (e.g., prednisolone, azathioprine)
- Thymectomy
- Rituximab
What is a myasthenic crisis?
A potentially life-threatening complication causing acute worsening of symptoms, often triggered by another illness
e.g. respiratory muscle weakness
Patients may need NIV or mechanical ventilation
What are the treatments for myasthenic crisis?
- IV immunoglobulins
- Plasmapheresis
