Myasthenia Gravis

Question 1

Myasthenia Gravis (MG)

Answer 1

An autoimmune disease
-acquired

Characterized by fluctuating weakness of certain muscle groups

Course of the disease variable:

• Short-term remission
• Stabilization
• Severe, progressive

Question 2

MG: Etiology

Answer 2

Risk Factors:

• Age: 10-65
• Gender: women

Etiology:
-Same as every other autoimmune disease!

Question 3

Pathogenesis

Answer 3

Antibodies attack ACh receptors
-AKA “anti-ACh antibodies”

Decrease in ACh receptor sites at the NMJ

This prevents ACh molecules from attaching and stimulating muscle contraction

Diminished nerve impulse to the muscle

Question 4

Clinical Manifestations

Answer 4

Fluctuating weakness of skeletal muscle

Strength comes back after resting

Muscle involved:

• Eyes/eyelids
• Facial
• Speaking
• Breathing

Question 5

Myasthenic Crisis

Answer 5

Acute exacerbation of muscle weakness Triggered by Stressor:

• Infection
• surgery
• emotional distress
• pregnancy/menses’
• inadequate pharmacotherapy or other drugs

Major complication:
-Breathing muscle weakness

Question 6

MG: Pharm

Answer 6

1. Immunosuppressants
2. Cholinesterase Inhibitors

How do Cholinesterase inhibiters work?

• Prevent inactivation of ACh by cholinesterase
• Intensify the effect of ACh release from the motor neurons: Increases muscle strength

Are cholinesterase inhibitors a cure or symptomatic relief?
-Only symptoms

Multiple administration routes

Question 7

Neostigmine (Prostigmin)

Answer 7

Class:
-Cholinesterase Inhibitor (anticholinesterase)

Indication:
-MG

MOA:
-In therapeutic doses, this drug affects both muscarinic and nicotinic receptors

Question 8

CNS (where are receptors located)

Answer 8

Glands, Adrenal, sweat, blood vessels, skeletal muscles

Question 9

Cholinergic VS Anticholinergics (EXAM)

Answer 9

CHOLINERGICS
GI Tract: Inc motility
Mouth: Inc secretions
Bladder: urinary urgency
Heart: Brady
Lungs: Bronchial Constrict
Eyes: Miosis (constrict)

ANTICHOLINERGICS
GI Tract: Dec motility
Mouth: Dry mouth
Bladder: Urinary retention
Heart: Tachycardia
Lungs Bronchodilation
Eyes: Mydriasis (dilation)

Question 10

Neostigmine: AE

Answer 10

Muscarinic:

• Inc secretions, Motility
• Urinary Urgency
• Bradycardia
• Bronchiole Constriction
• Miosis, near-sightedness

Neuromuscular (Nicotinic)
-Therapeutic doses: Increased muscle contraction
-Toxic doses: reduced contraction
TOXICITY: Cholinergic Crisis

Question 11

Cholinergic Crisis

Answer 11

Extreme muscle weakness or paralysis

S/S of excessive muscarinic stimulation

Treatment:

• Mechanical ventilation
• Antidote for muscarinic Sx: ATROPINE

What should the patient wear at all times?
-Med alert bracelet

Question 12

MG crisis VS Cholinergic crisis

Answer 12

MG Crisis:

• Not enough stimulation of ACh
• Muscles are not stimulated and weak (leading to respiratory failure)

Cholinergic crisis:

• Too much ACh or Neostigmine
• Overstimulation of muscles and muscles are worn out. (leading to respiratory failure)

Question 13

How can we tell the difference in a patient?

Answer 13

Client presents with respiratory insufficiency, extreme muscle weakness

Give Edrophonium

• a short acting cholinesterase inhibitor
• Increases ACh temporarily

If they are in MG crisis, they will improve because there is an increase in ACh

If they are in a cholinergic crisis, they will worsen because they already have too much ACh