Myasthenia gravis Flashcards
What is myasthenia gravis
autoimmune condition affecting the neuromuscular junction that causes muscle weakness that progressively worsens with activity and improves with rest
Who does myasthenia gravis normally effect
women under 40 and men over 50
What condition has a strong link with myasthenia gravis
thymomas
What antibody is found in most patients with myasthenia gravis
Acetylcholine receptor antibodies
What does AchR antibodies cause
they bind to the postsynaptic acetylcholine receptors, blocking them and preventing stimulation by acetylcholine
How can AchR antibodies cause further damage in myasthenia gravis
they activate the complement system in the neruomusclar junction leading to cell damage at the post synaptic membrane
What other antibodies can be found in patients with myasthenia gravis
- Muscle specific kinase antibodies (MuSK)
- Low density lipoprotein receptor lead protein 4 (LRP4)
What are MuSK and LRP4 important for
the creation and organisation of the Ach receptor
What is the clinical feature that is helpful in diagnosing myasthenia gravis
weakness worsens with exercise and improves with rest
Where does myasthenia gravis tend to affect most
proximal muscles of limbs and small muscles of head and neck
What are some common symptoms of myasthenia gravis
- difficulty climbing stairs
- diplopia due to extraocular muscle weakness
- ptosis due to eyelid weakness
- facial weakness
- difficulty swallowing
- jaw fatigue
- slurred speech
What are some ways to elicit symptoms in myasthenia gravis
- repeated blinking
- looking up for a long time
- repeatedly abducting arm
What investigations are done in myasthenia gravis
- Ach receptor antibodies
- MuSK antibodies
- LRP4 antibodies
- CT or MRI to check for thymoma
- endrophonium test if in doubt
What is the endrophonium test
endrophonium chloride (drug) given as it blocks enzymes that break down acetylcholine to see if it improves symptoms
What is the treatment for myasthenia gravis
- pyridostigmine- cholinesterase inhibitor which prolongs action of acetylcholine and improves symptoms
- immunosuppression via prednisolone or azathioprine which suppresses the production of antibodies
- thymectomy
- rituximab (monoclonal antibody against B cells) considered where other treatment fails
