Module 11 - Myasthenia Gravis

Question 1

Myasthenia Gravis (MG)

Answer 1

Disorder of transmission at the neuromuscular junction

It affects transmission of nerve impulses between motor neurons and the muscle cells it tries to innervate

Question 2

What age does MG usually occur?

Answer 2

Can occur at any age but the peak is 20-30 years old

Question 3

How does MG compare between sexes?

Answer 3

it is 3x more common in women than men under 40

After 50 there is a peak where men get it more

Question 4

What does Myasthenia Gravis mean

Answer 4

Grave Muscular Weakness

Question 5

What is the pathophysiology of Myasthenia Gravis

Answer 5

Autoimmune in nature

Antibody mediated destruction of acetylcholine receptors in the NMJ occur

This may be because of abnormal T Lymphocyte function (Thymic abnormalities)

Question 6

MG is characterized by what?

Answer 6

fluctuating weakness of muscle groups

Question 7

__% of those with MG have thymic abnormalities

Answer 7

75%

This is Thymoma or Thymic Hyperplasia

Question 8

MG is a problem with ___

Answer 8

acetylcholine

Question 9

Acetylcholine is commonly seen in what system?

Answer 9

the PNS (that’s why muscles weaken in MG)

Question 10

How does AP normally affect contraction of smooth, skeletal, voluntary, and cardiac muscles?

Answer 10

AP travels down the motor neuron and causes acetylcholine release into the synaptic cleft

This then binds to nicotinic receptors to open Na channels to have Na flood the post synaptic cell and result in contraction of all skeletal and voluntary muscles and impact smooth and cardiac muscles

Question 11

Manifestations of MG

Answer 11

Ptosis

Weakness in arms and legs

Difficulty breathing

Problems with chewing and swallowing

Blurred or double vision

Slurred Speech (from progressive weakness in facial muscles)

chronic Muscle fatigue

Question 12

One of the initial symptoms of MG is…

Answer 12

Diplopia (Double vision)

Question 13

What areas are most commonly effected by MG?

Answer 13

eye and periorbital muscles

You see drooping of eyelid from eyelid weakness and also double vision or blurred vision from weakens of extraocular muscles

Question 14

Ptosis in MG can lead to…

Answer 14

difficulties reading and ADL

Question 15

How can MG progress

Answer 15

it can progress from ocular muscle weakness to generalized weakness including respiratory muscle weakness

Question 16

How does extremity weakness present itself in MG

Answer 16

extremity weakness is usually greater in the proximal parts rather than distal parts - so limb weakness

Question 17

When are MG symptoms “at their quietest”

Answer 17

for many, in the morning - they grow worse with effort and throughout the day

Question 18

Myasthenia Crisis

Answer 18

Sudden exacerbation of symptoms, most seriously affecting respiratory muscles

May require ventilatory support and close airway management

Question 19

When does Myasthenia crisis usually occur

Answer 19

during stressful periods like infection, post-surgery, pregnancy, alcohol use, etc

Question 20

What things are done to diagnose MG

Answer 20

H&P Examination - thorough

Anticholinesterase testing

Nerve and Muscle Stimulation Studies

testing for Acetylcholine receptor antibodies

Question 21

Anticholinesterase Test

Answer 21

Uses Tensilon, a short acting acetylcholinesterase inhibitor via IV to decrease breakdown of acetylcholine

If MG is present, there will be dramatic improvement in muscle function

Question 22

Treatments for MG

Answer 22

Medications: Anticholinesterase drugs, Immunosuppressants, corticosteroids
Plasmapheresis

IV Immunoglobulins

Thymectomy

Question 23

Anticholinesterase drugs

Answer 23

inhibit the breakdown of Acetylcholine in MG patients

Question 24

Plasmapheresis

Answer 24

removes antibodies from circulation

short term clinical improvement

can stabilize MG during myasthenia crisis

often used alongside immunosuppressants

Question 25

Corticosteroids and MG

Answer 25

suppress immune response and are used with poor response to anticholinesterase drugs or those who had a thymectomy

Question 26

IV Immunoglobulin and MG

Answer 26

short term effect

expensive

beneficial because it facilitates improvement for weeks to months though

Question 27

Thymectomy

Answer 27

controversial fix for MG - since it has negative effect

removal of the thymus

can be done regardless of age with someone with thymoma or someone with generalized MG with onset before 50 yo