Myasthenia Gravis Flashcards
What is myathenia gravis?
CHronic autoimmune disorder (T2 Hypersensitivity) of the post synaptic membrane at NMJ.
What do autoimmune antibodies target in MG?
Against
AChR - acetyl choline receptors
MUSK - Muscle specific kinase
MUSK is involved in the AchR expression
What are the RF for MG
Female 2:1 Male
Fhx
Autoimmune diseases
Thymoma (cancer of lymphs)
What is the pathophysiology of Myasthenia gravis?
1st SIGNS : Extraocular muscles - Diplopia
and weak eyelids (unilateral ptosis)
weakness begins head the travel down
Fatigability - (gets progressivley weaker on exertion and imporve upon rest)
Myasthenia Gravis IVx
Primary investigations:
Antibodies: AchR antibodies/ Anti-MUSK (IgG)
Electrophysiological studies: repetitive nerve stimulation shows a decremental muscle response
CT thorax: Exclude thymoma
tensilon/edrotropium test - give edrotropium(Achase Inhibtior) and check for response
Myasthenia Gravis tx
1st :Acetylcholinesterase inhibitor : pyridostigmine
2nd: Prednisolone if Sx
3rd - Azathioprine
4th - methotrexate/azthioprine
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Whats a myasthenic crisis?
It is a complication of myasthenia gravis due to weakening of the respiratory muscles and is often provoked by infections or medications.
Patients present with: increasing shortness of breath, which can deteriorate into respiratory failure.
TX w/ IV Ig / plasmapharesis
Intubation and manual ventilation if severe resp compromise
corticosteroid
Myasthenia Gravis DDx
lambert Eaton syndrome
Autoimmuen disorder- Ab against Calcium chanels
Also shows muscle weakness but differes as it gets better with exertion and begin with the body then head
associated with SCLC
Tx prednisolone +IgG
Which drugs should be avoided in myasthenia gravis patients?
Anything that may affect cholinergic transmission can potentiallly exacerbate symptoms and may lead to myasthenic crisis
Lithium
pheytoin
all Beta blockers
antibiotics
neuromuscular blocking agents
