Myasthenia gravis (zero to finals) Flashcards
What is myasthenia gravis?
Myasthenia gravis is an autoimmune condition affecting the neuromuscular junction.
It causes muscle weakness that progressively worsens with activity and improves with rest.
Who is typically affected by myasthenia gravis?
Myasthenia gravis affects men and women at different ages, typically affecting women under 40 and men over 60.
What tumour type has a strong link with myasthenia gravis?
Thymomas (thymus gland tumours)
How are muscle contractions stimulated?
Motor neurones communicate with muscles via the neuromuscular junction. On one side of the synapse is the presynaptic membrane of the axon terminal of the motor neurone.
On the other side is the postsynaptic membrane of the motor end plate of the muscle cell.
The axons release a neurotransmitter called acetylcholine from the presynaptic membrane.
Acetylcholine travels across the synapse and attaches to receptors on the postsynaptic membrane, simulating muscle contraction.
What antibody type is found mostly in myasthenia gravis?
Acetylcholine receptor (AChR) antibodies are found in most patients with myasthenia gravis.
These antibodies bind to the postsynaptic acetylcholine receptors, blocking them and preventing stimulation by acetylcholine.
Why are myasthenia gravis symptoms more prominent during muscle activity?
The more the receptors are used during muscle activity, the more they become blocked.
There is less effective stimulation of the muscle with increased activity. With rest, the receptors are cleared, and the symptoms improve.
What are the 2 other antibody types that may be present in myasthenia gravis?
Muscle-specific kinase (MuSK) antibodies
Low-density lipoprotein receptor-related protein 4 (LRP4) antibodies
Why are MuSK and LRP4 important proteins?
They are important for the creation and organisation of the acetylcholine receptor.
Destruction of these proteins leads to inadequate acetylcholine receptors.
What are the main critical clinical features of myasthenia gravis?
Weakness that worsens with muscle use and improves with rest.
Symptoms are typically best in the morning and worst at the end of the day.
Most myasthenia gravis symptoms affect the proximal muscles of the limbs and small muscles of the head and neck. What do these include?
Difficulty climbing stairs, standing from a seat or raising their hands above their head
Extraocular muscle weakness, causing double vision (diplopia)
Eyelid weakness, causing drooping of the eyelids (ptosis)
Weakness in facial movements
Difficulty with swallowing
Fatigue in the jaw when chewing
Slurred speech
What actions elicit fatiguability in the muscles?
Repeated blinking will exacerbate ptosis
Prolonged upward gazing will exacerbate diplopia on further testing
Repeated abduction of one arm 20 times will result in unilateral weakness when comparing both sides
What do antibody tests for myasthenia gravis check for?
AChR antibodies (around 85%)
MuSK antibodies (less than 10%)
LRP4 antibodies (less than 5%)
Why would a CT or MRI be used for myasthenia gravis?
A CT or MRI of the thymus gland is used to look for a thymoma.
What are the treatment options for myasthenia gravis?
Pyridostigmine is a cholinesterase inhibitor that prolongs the action of acetylcholine and improves symptoms
Immunosuppression (e.g., prednisolone or azathioprine) suppresses the production of antibodies
Thymectomy can improve symptoms, even in patients without a thymoma
Rituximab (a monoclonal antibody against B cells) is considered where other treatments fail
What is a myasthenic crisis?
A potentially life-threatening complication of myasthenia gravis.
It causes an acute worsening of symptoms, often triggered by another illness, such as a respiratory tract infection.
