Myasthenia Gravis Flashcards
What is myasthenia Gravis
Autoimmune disorder involving the destruction of neuromuscular junctions and Aceytalcholine
Describe the normal Pathophysiology behind acetylcholine
ACT is formed at neuromuscular junction and stored in vesicles.
Action potential travels down the neuron releasing ACT into synapse where it binds to ACT receptors
ACT releases cations into the receiving muscle cell, depolarizing the end plate of the muscle cell causing muscular contraction
What happens to ACT in Myasthenia Gravis
There is a lack of ACT receptors at receiving muscle cell. The decreased cation release produces a smaller or fails to produce muscular contraction
Myasthenia Gravis s/s
Fatigue after repeated use, worse at the end of the day, improves following rest or sleep
ranial muscles
◦ Eye lids and extraocular muscles (EOMs)
◦ Diplopia and ptosis common initial complaints
◦ Ocular MG if weakness remains restricted only to
extraocular muscles for 3 years
◦ Dysphagia
◦ Bulbar weakness
◦ Respiratory depression
◦ Especially prominent in MuSK antibody–positive MG
◦ Vent support if in crisis
◦ Generalized weakness affecting limb muscles
◦ Often proximal & can be asymmetric
◦ Preserved deep tendon reflexes
What is the ice pack test in myasthenia Gravis
Apply ice pack over ptotic eye
If this results in ptosis improvement
Due to NMJ defect
Describe autoantibody testing in MG
• Anti-AChR antibodies
• Virtually diagnostic of MG
• Negative test does not exclude MG
• Anti-Ach, Anti-MuSK antibody, Anti-LRP4 antibody
Describe electro diagnostic testing in MG
• Repetitive nerve stimulation
• Positive if rapid reduction of >10% in amplitude of evoked responses
describe Anticholinergic testing for MG
• Preserved for antibody negative clinical MG
• Edrophonium IV dose 2 mg administered
• Definite improvement occurs, test is considered positive
• No change
• Give additional 8 mg in two (2) parts
• Keep Atropine nearby
Pharmacological treatment for MG
Pyridostigmine: Cholinesterase inhibitor
Glucocorticoids
Rituximab: immunosuppressants
Plasmaphoreis
IVIG
Surgical options for MG
Thymectomy
What is a MG crisis
Weakness that impairs the diaphragm
What are the s/s of a cholinegic Crisis
S&S: Excessive sweating, increased salivation, diarrhea, abdominal cramping, muscle weakness, difficulty breathing
Treatment of a cholinergic crisis
◦ Treatment Plan
◦ Stop offending agent(s), Atropine 2 mg, airway
What is the most common trigger for MS crisis
◦ Most common cause of MG crisis
◦ Intercurrent infection
Treatment plan for MS crisis
◦ Treatment Plan
◦ ICU admission
◦ Antibiotic therapy
◦ Ventilatory assistance
◦ Pulmonary physiotherapy
◦ Plasmapheresis or IVIg
◦ Avoid certain drugs (see table in module)
