Myasthenia gravis Flashcards
What is it?
Autoimmune condition affecting the neuromuscular junction
Causes muscle weakness that progressively worsens with activity and improves with res t
What age at each sex does it typically affect?
women under 40
men over 60
What does MG have a strong association with?
Thymomas
Explain the pathophysiology
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. 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.
Antibodies also activate the complement system within the junction leading to cell damage at the postsynaptic membrane worsening sx further
What antibodies can cause MG?
Acetylcholine receptor abs
Muscle specific kinase abs
Low-density lipoprotein receptor related protein 4 abs
What is the most critical feature of MG?
Weakness worsens with muscle use and improves with rest therefore
Sx are best in the morning and worse at the end of the day
What muscles are mostly affected?
proximal muscles of the limbs
small muscles of the head and neck
What are the symptoms
Difficulty climbing stairs
Standing from seated
Raising hands above their head
Extraocular muscle weakness - diplopia
Eyelid weakness - ptosis
Weakness in facial movements
Difficulty swallowing
Fatigue in the jaw when chewing
slurred speech
What movements can elicit fatiguability in the muscles?
Repeated blinking -> ptosis
Prolonged upward gazing -> diplopia
Repeated abduction of one arm 20 times -> unilateral weakness
What might you look for on examination that may give a clue to the diagnosis ?
Thymectomy scar
What investigations would you do ?u
AChR abs
MuSK abs
LRP4 abs
CT/MRI of thymus gland
Edrophonium tets
What is the edrophonium test
Pt is given edrophonium chloride (neostigmine)
Normally cholinesterase enzymes in the neuromuscular junction break down acetylcholine
Edrophonium blocks these enzymes therefore there is more acetylcholine and temporarily relieves the weakness
What are medical therapy treatment options?
Pyridostigmine - cholinesterase inhibitor
immnosuppression - prednisolone or azathioprine
Rituximab
What surgical option is there?
Thymectomy even if they dont have a thymoma
What is a myasthenia crisis? What triggers it
Life threatening complication of mG
Often triggered by another illness e.g. resp tract infectionW
