Module 11 - Myasthenia Gravis Flashcards
Myasthenia Gravis (MG)
Disorder of transmission at the neuromuscular junction
It affects transmission of nerve impulses between motor neurons and the muscle cells it tries to innervate
What age does MG usually occur?
Can occur at any age but the peak is 20-30 years old
How does MG compare between sexes?
it is 3x more common in women than men under 40
After 50 there is a peak where men get it more
What does Myasthenia Gravis mean
Grave Muscular Weakness
What is the pathophysiology of Myasthenia Gravis
Autoimmune in nature
Antibody mediated destruction of acetylcholine receptors in the NMJ occur
This may be because of abnormal T Lymphocyte function (Thymic abnormalities)
MG is characterized by what?
fluctuating weakness of muscle groups
__% of those with MG have thymic abnormalities
75%
This is Thymoma or Thymic Hyperplasia
MG is a problem with ___
acetylcholine
Acetylcholine is commonly seen in what system?
the PNS (that’s why muscles weaken in MG)
How does AP normally affect contraction of smooth, skeletal, voluntary, and cardiac muscles?
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
Manifestations of MG
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
One of the initial symptoms of MG is…
Diplopia (Double vision)
What areas are most commonly effected by MG?
eye and periorbital muscles
You see drooping of eyelid from eyelid weakness and also double vision or blurred vision from weakens of extraocular muscles
Ptosis in MG can lead to…
difficulties reading and ADL
How can MG progress
it can progress from ocular muscle weakness to generalized weakness including respiratory muscle weakness
How does extremity weakness present itself in MG
extremity weakness is usually greater in the proximal parts rather than distal parts - so limb weakness
When are MG symptoms “at their quietest”
for many, in the morning - they grow worse with effort and throughout the day
Myasthenia Crisis
Sudden exacerbation of symptoms, most seriously affecting respiratory muscles
May require ventilatory support and close airway management
When does Myasthenia crisis usually occur
during stressful periods like infection, post-surgery, pregnancy, alcohol use, etc
What things are done to diagnose MG
H&P Examination - thorough
Anticholinesterase testing
Nerve and Muscle Stimulation Studies
testing for Acetylcholine receptor antibodies
Anticholinesterase Test
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
Treatments for MG
Medications: Anticholinesterase drugs, Immunosuppressants, corticosteroids
Plasmapheresis
IV Immunoglobulins
Thymectomy
Anticholinesterase drugs
inhibit the breakdown of Acetylcholine in MG patients
Plasmapheresis
removes antibodies from circulation
short term clinical improvement
can stabilize MG during myasthenia crisis
often used alongside immunosuppressants
Corticosteroids and MG
suppress immune response and are used with poor response to anticholinesterase drugs or those who had a thymectomy
IV Immunoglobulin and MG
short term effect
expensive
beneficial because it facilitates improvement for weeks to months though
Thymectomy
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
