Week 10 - Myasthenia Gravis Flashcards
what is myasthenia gravis
- an autoimmune disease affecting the neuromuscular junction
- causes normal communication between the nerve & muscle to be interupted at the place where the nerves connect to the muscle (neuromuscular junction)
how does the typical neuromusclar junction work
- signal travels down the motor nerve
- the nt Ach is released & binds to ach receptors on the muscle
- the binding then activated the muscle & causes a muscle contraction
describe the neuromuscular junction in myasthenia gravis
- antibodies block or destroy the ach receptors at the neuromuscular junction = no muscle contraction
what is the hallmark of myasthenia gravis
- muscle weakness that worsens after periods of activity
- but improves after periods of rest
- often wake up feeling fine in the morning, but worsens as the day progresses
list symptoms of myasthenia gravis (6)
- muscle weakness
- ptosis
- diplopia
- dysphagia
- dysarthria
- difficulty breathiing
what is ptosis
- drooping of the eye lid
describe diagnosis of myasthenia gravis
- history & physical exam
- serum testing for ach receptor antibodies
- EMG
what is an EMG
- electromyography
describe the use of an EMG for myasthenia gravis diagnosis
- repetitive electrical stimulation is delivered to a motot nerve repeatedly, several times/second
- the EMG can detect impaired muscle to impaired nerve-muscle transmission
what can trigger myasthenia gravis
- autoimmune disorders so
- stress, fatigue, infection
what class of meds is used for myasthenia gravis
- cholinesterase inhibitor
what type of cholinesterase inhibitor is used for myasthenia gravis
- neostigmine
what is the MOA of neostigmine
- binds to cholinesterase & prevents breakdown of ach by the enzyme cholinesterase
= increased amt of ach available
what are adverse effects of neostigmine (5)
- excessive salivation
- increased gastric secretion
- increased GI motility
- bradycardia
- urinary urgency
what causes the adverse effects of neostigmine
- accumulation of ach which is responsible for PSNS
what can toxic doses of neostigmine cause
- resp depression thru paralysis of respiratory muscle
what is an emergency associated w myasthenia gravis
- myasthenic crisis
what is myasthenic crisis
- acute exacerbation of muscle weakness
what can trigger myasthenic crisis (4)
- infection
- surgery
- stress
- fatigue/insomnia
when does myasthenic crisis occur
- within the first 2 years of diagnosis
what is the concern w myasthenic crisis
- the resp muscle weaken
- which can cause dyspnea, increased WOB
- and may require a ventilator & can be fatal
