Myasthenia Gravis

Question 1

What is myasthenia gravis?

Answer 1

An autoimmune disease characterized by fluctuating weakness of certain muscle groups

Question 2

What are the risk factors for myasthenia gravis>

Answer 2

Women, 10-65 years olf

Question 3

What is the patho behind myasthenia gravis?

Answer 3

Antibodies attach to acetylcholine receptors (these are anti-acetylcholine receptor antibodies)
There is a decrease in ACh receptor sits at the neuromuscular junctions
This prevents ACh molecules from attaching and stimulating muscle contractions

Question 4

What are the manifestations of myasthenia gravis?

Answer 4

Fluctuating weakness of skeletal muscle (strength usually comes back after resting)

Question 5

What muscles are involved in myasthenia gravis?

Answer 5

Eyes / eyelids
Facial
Muscles related to speaking, breathing

Question 6

What muscles are less affected in myasthenia gravis?

Answer 6

Shoulder and hips

Question 7

What is a myasethenic crisis?

Answer 7

Acute exacerbation of muscle weakness usually triggered by a stressor

Question 8

What is the major complication of a myasthenic crisis?

Answer 8

Compromise of the breathing muscles, having a greater risk of respiratory arrest

Question 9

How do cholinesterase inhibitors work for myasthenia gravis?

Answer 9

Prevent inactivation of ACh by cholinesterase which intensifies the effects of ACh released from motor neurons (increases muscle strength). This doesn’t cure MG because it doesn’t effect the antibodies.

Question 10

What class of medication is neostigmine?

Answer 10

Cholinesterase inhibitor

Question 11

What two receptors does neostigmine work on?

Answer 11

Muscarinic and nicotinic

Question 12

What are the side effects of neostigmine?

Answer 12

From muscarinic receptors: increased motility, diarrhea, increased secretions, urinary urgency, bradycardia, bronchial constriction, pupil constriction
From nicotinic receptors: increased muscle contraction (in toxic doses = reduced contraction)

Question 13

Where are nicotinic receptors located?

Answer 13

CNS and neuromuscular junctions

Question 14

Where are muscarinic receptors located?

Answer 14

Peripheral and CNS - innervating visceral organs

Question 15

What is a cholinergic crisis?

Answer 15

Extreme muscle weakness or paralysis
s/s of excessive muscarinic stimulation

Question 16

What is the antidote for muscarinic symptoms?

Answer 16

Atropine

Question 17

Compare myasthenia gravis crisis and a cholinergic crisis:

Answer 17

MG crisis: not enough ACh which means the muscles are not stimulated and are weak
(can lead to respiratory failure)
Cholinergic crisis: Too much ACh which means there is an overstimulation of muscles that leads to fatigue and wearing out (which can lead to respiratory failure)

Question 18

What medication can be given to differentiate between a myasthenia gravis crisis and a cholinergic crisis?

Answer 18

Edrophonium - this is a short acting cholinesterase inhibitor which causes a build up of ACh
If patient has MG crisis = symptoms will improve
If patient has cholinergic crisis = they will get worse