Myasthenia Gravis

Question 1

myasthenia gravis

Answer 1

• decreased available ACh receptors at post-synaptic site of neuromuscular junction due to destruction by circulating antibodies
• muscle weakness, respiratory insufficiency, aspiration, cardiomyopathy, cardiac failure
• thymectomy–for drug-resistan disease

Question 2

symptoms

Answer 2

• ptosis, diplopia, dysphagia
• inc risk of respiratory failure and aspiration
• cardiac muscle impaired 2/2 cardiomyopathy
• smooth muscle not affected (e.g. bladder)

Question 3

types

Answer 3

TypeI I: extraocular muscles
Type IIa: mild, with muscles of respiration spared
Type IIb: more rapidly progressive with muscles of respiration involved
Type III: acute onset, rapid progression, high mortality
Type IV: severe form–progression of I or II

Question 4

work-up

Answer 4

• degree skeletal/cardial muscle involvement (PFT, ABG)
• tensilon test
• pt education -prolonged ventilation postop
• no preop sedation

Question 5

tensilon test

Answer 5

• edrophonium–short acting anticholinesterase
• 2-10 mg IV inhibits acetylcholinesterase that normal breaks down Ach
• build up of AcH at NMJ
• myasthenic crisis: strenghth improves
• cholinergic crisis: worsens (SLUDE+bradycarida

Question 6

conditions c/w cholinergic crisis

Answer 6

SLUDE+bradycardia, bronchoconstriciton, ciliary constriction
-salivation, lacrimation, urination, defecation, erection

Question 7

RX cholinergic crisis

Answer 7

-administer atropine, maintain oxygenation and ventilation

Question 8

RX myasthenic crisis

Answer 8

-administer neostigmine

Question 9

NM blockade

Answer 9

• can have resistance to succs

- defasciculating dose of nondepolarizer is enough to cause paralysis (1/5 normal nondepolarizer

Question 10

In labor

Answer 10

• continue anticholinesterase therapy

- use sedatives with caution

Question 11

neonatal myasthenia

Answer 11

• 20-30% neonates whose mothers are afflicted
• generalized weakness
• anticholineserase therapy usu needed for 3-4 weeks after birth
• newborns are at higher risk to develop respiratory insufficiency

Question 12

Eaton Lambert–myasthenic syndrome

Answer 12

• associated with bronchial carcinomas–muscular weakness
• also in pts with thyroid disease and SLE
• caused by dec Ach release following nerve stimulation (presynaptic)

Question 13

Eaton Lambert-Symptoms

Answer 13

• increased muscle strength with exercise, no improvement following admin of anticholineresase
• proximal muscles of limbs, not bulbar muscles

Question 14

Eaton lambert-NM blockers

Answer 14

-marked sensitivity to both depolarizers and nondepolarizers

Question 15

myasthenia gravis: pyridostigmine

Answer 15

• neostigmine or pyridostigmine are anticholinesterase drugs sued to treat myasthenia gravis
• inhibit enzyme responsible for hydrolysis of Ach (acetylcholinesterase)–increase amt of neurotransmitter available at the NMJ
• pyridostigmine lasts longer than neostigmine (3-6 hr)–produces muscarinic side effects–po dose 60 mg=IM/IV 2mg
• phosphline iodide-v. ptoent anticholinesterase drug used for pts with severe myastenia
• excess anticholinesterase can result in skeletal muscle weakness (cholinergic crisis)