Myasthenia Gravis Flashcards
what is myasthenia gravis?
–autoimmune
–characterized by fluctuating weakness of certain muscle groups
course of disease for MG
variable
–short term remission
–stabilization
–severe, progression
risk factors for MG
–age: 10-65 years
–women
patho for MG
–antibodies attack ACh receptors
–decrease in ACh receptor sites at the neuromuscular junction
–prevents ACh molecules from attaching and stimulating muscle contraction
symptoms of MG
–fluctuating weakness of skeletal muscle
–strength comes back after resting
what muscles are involved in MG?
–eyes/eyelids
–facial
–speaking
–breathing
myasthenic crisis
acute exacerbation of muscle weakness
what is a myasthenic crisis triggered by?
–infection
–surgery
–emotional distress
–pregnancy/menses
–inadequate pharmacotherapy or other drugs
major complication of myasthenic crisis
breathing muscle weakness
MG pharm
–immunosuppressants (steroids)
–cholinesterase inhibitors
how do cholinesterase inhibitors work?
–prevent inactivation of ACh by cholinesterase
–intensify effects of ACh released from motor neurons –> increases muscle strength
when should cholinesterase inhibitors be given?
give 30-45 minutes prior to eating to strengthen swallowing muscles
example of cholinesterase inhibitor
neostigmine (Prostigmin)
MOA of neostigmine
–enhances cholinergic action by facilitating transmission of impulses across neuromuscular junctions
–in therapeutic doses, affects muscarinic and nicotinic receptors
effect of cholinergics on GI tract
–increased motility
–diarrhea
effect of anticholinergics on GI tract
–decreased motility
–constipation
effect of cholinergics on mouth
increased secretions
effect of anticholinergics on mouth
dry mouth
effect of cholinergics on bladder
urinary urgency
effect of anticholinergics on bladder
urinary retentione
effect of cholinergics on heart
bradycardia
effect of anticholinergics on heart
tachycardia
effect of cholinergics on lungs
bronchial constriction
effect of anticholinergics on lungs
bronchodilation
effect of cholinergics on eyes
miosis (constriction)
effect of anticholinergics on eyes
mydriasis (dilation)
neostigmine adverse effects (muscarinic)
–increased secretions, GI motility
–urinary urgency
–bradycardia
–bronchial constriction
–miosis, near-sightedness
neostigmine adverse effects (neuromuscular/nicotinic)
–therapeutic doses = increased muscle contraction
–toxic doses = reduced contraction
–toxicity –> cholinergic crisis
cholinergic crisis
–extreme muscle weakness or paralysis
–s/s of muscarinic stimulation
treatment for cholinergic crisis
–mechanical ventilation
–antidote for muscarinic symptoms = atropine
what should the MG patient wear at all time?
med alert bracelet
MG crisis vs. cholinergic crisis
MG crisis
–not enough stimulation or acetylcholine
–muscles are not stimulated and weak
–leads to respiratory failure
Cholinergic crisis
–too much acetylcholine or nystigmine
–overstimulation of muscles and muscles are worn out
–leads to respiratory failure
how to differentiate between MG or cholinergic crisis?
–give EDROPHONIUM
–if they improve = MG crisis because increase in acetylcholine
–if they worsen = cholinergic crisis because too much acetylcholine
edrophonium
short acting cholinesterase inhibitor that increases acetylcholine temporarily
