Myasthenia Gravis Flashcards
Myasthenia Gravis is an a________ response against…
autoimmune
NMJ post-synaptic receptors
What type of hypersensitivity reaction is myasthenia gravis?
Type 2
True or false: often patients with Myasthenia Gravis wake up feeling fine and by the end of the day feel weak
True
Myasthenia gravis affects ______ muscle
skeletal
In myasthenia gravis, what symptoms occur when the extraocular muscles are affected?
Diplopia (double vision)
Ptosis
What groups of people are at higher risk of Myasthenia Gravis?
20-30 y/o women
and
60-70 y/o men
(unclear why this bimodal distribution)
What does acetylcholine, released from motor neuron, bind to on the muscle cell membrane at a NMJ?
Nicotinic acetylcholine receptor
In myasthenia gravis, what cells make the autoantibodies that bind to the nicotinic ACh receptors on muscle cell membrane?
B cells
Give a summary of the pathophysiology of Myasthenia gravis
Type II hypersensitivity reaction results in B cells producing autoantibodies that bind to the nicotinic ACh receptors on the muscle cell membrane of NMJs, blocking ACh from binding. Therefore, muscle won’t contract.
A minority of people with Myasthenia Gravis produce the harmful antibody called muscle specific receptor t_____ k____ antibodies
tyrosine kinase
What do muscle specific receptor tyrosine kinase antibodies attack?
Proteins inside muscle cells also leading to destruction of healthy cells
Rarely, a p______ can generate an immune response which results in generation of autoantibodies (Lambert Eaton Syndrome)
paraneoplasm
What are symptoms of Myasthenia Gravis?
Muscle weakness
Weak eye muscles, diplopia
Ptosis
Myasthenic snarl (difficulty smiling)
Jaw fatigability
Swallowing difficulty
Speech fatigability
What worsens the muscle weakness in Myasthenia Gravis?
Exertion (better with rest)
Where do symptoms in Myasthenia Gravis start?
In head and neck and goes down to lower body
What condition presents very similarly to Myasthenia Gravis?
Lambert Eaton Syndrome
What happens in Lambert Eaton Syndrome?
There is autoimmunity against pre-synaptic calcium channels
True or false: Lambert Eaton Syndrome improves with exertion
True
Lambert Eaton Syndrome is associated with…
small cell lung carcinoma
How is Lambert Eaton Syndrome treated?
Steroids like prednisolone
and immunosuppression like IV Ig
Where do symptoms in Lambert Eaton Syndrome start?
Starts in extremities, then head and neck with autonomic involvement (eg. dry eyes and mouth), goes down to lower body
What could happen in a myasthenic crisis?
Acute symptoms worsening with a decreased function of breathing muscles
How do you treat respiratory weakness in a Myasthenic crisis?
Plasma exchange and immunosuppression (IV Ig)
How is Myasthenia Gravis managed?
1st line = Acetylcholinesterase inhibitors:
Neostigmine or Pyridostigmine
Immunosuppressive drugs:
Prednisone
Surgical removal of thymus (unknown exactly why, may be to do with T-helper cells originating in thymus help the B cells to make autoantibodies)
Last resort = Rituximab (monoclonal antibody against B cells)
How do acetylcholinesterase inhibitors work in Myasthenia Gravis?
Stop breakdown of ACh so increased concentration of ACh around muscle cells. Helps to counteract effects of ACh receptor antibodies.
Why is Prednisolone used in Myasthenia Gravis?
Reduces the production of autoantibodies
How do you diagnose Myasthenia Gravis?
Serology: Anti ACh-R
Edrophonium test: administer edrophonium (rapid acting ACh-ase inhibitor and will be increased muscle power in a few seconds for a few seconds.
10-20% patients with myasthenia gravis have a t____
thymoma
What 3 antibodies can cause myasthenia gravis?
ACh-receptor antibodies
Muscle-specific kinase antibodies (MuSK)
low density lipoprotein receptor-related protein 4 (LRP4)
