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What is Myasthenia Gravis?

Myasthenia gravis is a rare autoimmune disease that inhibits the action of acetylcholine to bind to receptors at the neuromuscular junction. This in turn hinders the voluntary muscles, causing them to become weak and fatigued, especially in times of activity.


Which muscles are most affect by Myasthenia Gravis?

The muscles affected most in the body are those around the eye, mouth, throat, and distal parts of the extremities.



-> Autoimmunity
-> Tigger unclear, thought to be sensitized helper T cells


What population is at Risk

Mostly Young women (20-30)

Men develop less often and later in life (70-80)


Patho of Myasthenia Gravis

Antibodies and sensitized T cells impair (block or attack?) muscle endplate at site of acetyl choline receptors preventing impulses from travelling across myoneural junction. -> voluntary muscle weakness.

Widened synaptic space and shedding of receptors rich folds


What endocrine gland is involved?

80% of people with myasthenia graves have thymus hyperplasia or thymus tumor.


Clinical Manifestations of MG

ptosis- eyelid drooping
diplopia- double vision
dysphonia- speech impairment (1st sign)
dysphagia- swallowing impairment (1st sign)

Generalized voluntary muscle weakness
Intercostal weakness (respiratory)

NOTE: Only Motor fx inhibited


What is the key Diagnostic test?

Acetylcholinesterase inhibitor test

Use endrophonium chloride (potent Ach ase inhibitor administered IV to increase ACh at neuromuscular junction. Ptosis and muscle weakness should resolve 5minutes post admin providing a positive result.


Other Diagnostic Tests?

Thymus gland will likely be enlarged (MRI)

EMG (electromyography) detects delay or failure of transmission.



First Line- Anticholinesterase (Mestinon)
-> inc ACH concentration by inhibiting breakdown of ACh


Ach Ase Inhibitors
immunosuppresive medications
IF nothing works Thymectomy


What is Plasmapheresis?

Used to treat exacerbations.

Plasma and Plasma components are removed using large catheter. Blood cells and antibody containing plasma are separated -> cells are reinfused with a plasma substitute.

=antibodies removed


What is a myasthenic crisis?

Myasthenic crisis is an intensification of disease process and involves an increase in muscle weakness (especially in the throat) and respiratory and bulbar weakness, which can cause the person to go into respiratory failure. This intensification is most commonly due to respiratory infection but can also be triggered by medication change, surgery, or pregnancy.