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Myasthenia gravis is a chronic autoimmune
neuromuscular disease that is characterized
by different degrees of weakness of the
skeletal muscles of the body. The name
myasthenia gravis came from a Latin and
Greek origin meaning grave muscle
weakness.
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Myasthenia Gravis is termed an autoimmune
disease. The immune system usually makes
antibodies to attack bacteria, viruses and
germs. With the autoimmune disease, the
immune system makes antibodies against
parts of ones own body tissues.
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Although there is no direct cause known for
why the body starts to produce the
antibodies that destroy the acetylcholine
receptors, it is believed to be related to the
thymus gland since it also produces
antibodies.
Onset usually occurs in women in the 18-25
year rage and men in the 60-80 year range
Myasthenia gravis affects approximately 20
in 100,000 people
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In a person with normal immune system,
muscles are stimulated to contract by the
transmission of nerve impulses to the
muscle fibers. The nerve impulses cause
neurotransmitter acetylcholine to be released
into the synaptic cleft. There it is picked up
by the acetylcholine receptors on the muscle
fiber.
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In myasthenia gravis, the numbers of
acetylcholine receptors appear to be reduced.
There is evidence to indicate that the
receptor deficit is caused by an attack on the
acetylcholine receptors by the body's own
immune system.
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With the numbers of acetylcholine receptors
reduced, it causes the nerve impulse to be
prevented from reaching the muscles. The
result is weakness and rapid fatigue only in
the affected muscles.
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About 60 % patients have weakness in the
eye muscles, termed ocular myasthenia.
The majority of other patients will go on to
develop weakness in other muscle groups.
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Other types of myasthenia gravis include
congenital MG, which is an inherited
condition caused by a genetic defect instead
of an immune disorder
It develops in an infant shortly after being
born to a mother with myasthenia gravis and
usually has generalized symptoms.
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Transient neonatal MG is a temporary
condition that develops in approximately 1020% of infants born to a mother with
myasthenia gravis
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It is caused by the circulation of the mothers
antibodies through the placenta and lasts as
long as the mothers antibodies remain in the
infant.
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Ocular manifestations
– Ptosis, uni- or bilateral is very common and
may occur while patients reading, or during
long period of driving
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Difficulty chewing, speaking, or swallowing:
initial symptoms in 17% of patients
Fatigability and weakness during mastication
Unable to keep jaw closed after chewing
Slurred and nasal speech
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Up to 75% of Pt’s have abnormality of thymus
25% have thymoma, tumor (either benign or
malignant) of thymus
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Limb muscles weakness:
– Initial symptoms in fewer than 10%
– Upper extremities weakness is more
common than lower extremities,
asymmetrical
– Involve proximal muscles than distal
– Involve neck muscles: neck flexion weaker
than neck extension
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Possible association
– Anticholinergic drugs (artane);
– Anti-infectives (ampicillin, imipenem,
erythromycin)
– Cardiovascular drugs (propafenone HCl,
verapamil);
– Cholroquine phosphate
– Neuromuscular-blocking drugs
(vecuronium,
succinylcholine)
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• Osserman Classification
Grade I: involve focal disease (restricted to
ocular muscle)
Grade II: generalized disease
IIa: mild
IIb: moderate
Grade III: severe generalized disease
Grade IV: a crisis with life-threatening
impairment of respiration
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The goal is to achieve remission
By increased neuromuscular transmission
Reduce autoimmunity
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blood tests are done to detect the abnormal
antibody that destroys the receptors
If spread out, in 2 y – thymectomy
 Acetylcholine-receptor antibody levels fall
 Immunosuppressive therapy
Cyclosporine
 Inhibits T-cell activation
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Electromyography Repetitive Nerve
Stimulation to check for a post-synaptic
defect or a muscle biopsy to look for
antibodies may also be used.
• Serologic tests(test clear portion of the blood) may
be used
• Chest x-ray
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MG is usually not fatal but in the case of a
myasthenia crises occurrence (when muscles
needed for breathing are affected),
hospitalization and intensive care may be
necessary to aid breathing with a respirator.
• Management
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– Stop every medications
– Assisted ventilation
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Vecuronium
Succinylcholine
Fentanyl
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Www.ctsnet.org/doc/4989
http://www.myasthenia.org/amg_whatism
g.cfm
http://en.wikipedia.org/wiki/Myasthenia_gr
avis
http://www.nlm.nih.gov/medlineplus/myas
theniagravis.html
http://www.sfn.org/index.cfm?pagename=
brainBriefings_MyastheniaGravis