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MG or grave muscle weakness
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Myasthenia gravis is a neuromuscular disorder (nerves and muscles) that causes weakness in the voluntary muscles, which are controlled by will or volition (i.e., chewing, swallowing, eye movements, legs, and arm movements).
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- The drooping of the upper eyelid and limitation of eye movements
- Difficulty holding the head up while lying the on back.
- Weakness increases with activity and decreases with rest
- Difficulty chewing, swallowing, talking, walking, and breathing
- Double vision, facial weakness, shortness of breath, and coughing.
- Weakness of muscles becomes more severe as the day progresses toward evening
- Symptoms fluctuate in the first 3 years, gradually becoming more severe. After many years (15-20), the condition stabilizes (i.e., the muscles become atrophic and permanently weak and shrunken).
- Some MG patients state that infections (caused by viruses), fever, stress, certain drugs or diseases (hypothyroidism, hyperthyroidism), and hormonal changes (menstruation and pregnancy) may worsen the symptoms.
- Myasthenia crisis happens in 10% of patients with severe involvement of respiratory (breathing) muscles, and the patient cannot breathe on his own, and may die without assistance from a respirator or ventilator.
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Autoimmune reaction -- the immune system uses specific
cells (white blood cells) and protein (antibodies) to fight
against infection, cancer, and toxic agents. Autoimmune
reactions occur when the immune system attacks the body
itself.
- In MG, antibodies destroy muscle
sites normally used for the reception of a molecule
(acetylcholine) needed for transmitting nerve impulses
(messages from brain) to the muscle.
- These auto antibodies are called
acetylcholine receptor antibodies or AchR.
- Genetic (inherited)
- abnormalities at the junction between nerve and muscle
(neuromuscular junction)
- Thymus gland -- a type of white
blood cell called T-Lymphocyte lives here. There are
various abnormalities of this gland in MG (overactive
thymus or tumors).
- Infants born to myasthenic mothers may have transient neonatal myasthenia gravis
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- Clinical history and exam by a doctor
- Tests include:
- A complete blood count (white and red blood cells), chemistries (liver and kidney function), and specific antibodies such as AchR (normal level does not exclude MG)
- Tensilon test -- single dose of edrophonium chloride intravenously (via veins) improves weakness (talking, chewing, and swallowing better).
- Pyridostigmine(mestinon) taken by mouth daily may improve weakness and help diagnose MG.
- Neostigmine given as an injection in the muscle lasts longer than edrophonium. If weakness improves, a diagnosis of MG is made.
- Electromyography (EMG) -- small needles attached to electrodes (wires) are inserted in the muscles. Then, electrical pulses are sent down the wire, which produces a characteristic electrical "jitter" in MG patients (not seen in normal people).
- Repetitive nerve stimulation (RNS) studies -- electrodes are attached to the skin, and the muscles are stimulated. One can see a less than normal muscle response in MG.
- Chest X-ray and CAT scan can show the thymus gland is enlarged, in the middle of the chest.
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- Infants born to myasthenic mothers
- Presence of hyperplastic (overactive) thymus is seen in 70% of MG cases
- Benign thymus tumors are seen in 10% of MG cases (i.e., the tumor is not cancer).
- There may be an association with autoimmune disorders (i.e., systemic Lupus erythromatosis, rheumatoid arthritis).
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- Anticholinesterase drugs (mestinon
=
pyridostigmine, and Prostigmin= neostigmine) inhibit the enzymes that break down acetylcholine in the body, allowing for muscle stimulation.
- Corticosteroids, such as prednisone, improve symptoms in 70 - 80% of cases.
- In the first week, the symptoms may get worse, but over the next 6-8 weeks, there may be improvement. There are side effects such as infection, fluid retention, or thinning of bones and skin.
- Oral immunosuppressants such as azathioprine(Imuran) or cyclosporine (both may be given with Prednisone) can reverse symptoms in most patients. Effects may take 2-4 months to develop. There may be serious side effects, such as infection, kidney damage, and high blood pressure.
- Cyclophosphamide is an immunosuppressant given intravenously that relieves symptoms in 50% of patients (infections can be a serious side effect).
- Intravenous immunoglobulin antibodies and filtering the blood (plasmapheresis) have short-term benefits in select patients with acute or sudden attacks.
- Plasmapheresis (separating the cellular elements from the blood)
- Thymectomy (surgical removal of the thymus) may be considered if there is no response to medications, and in those with eye symptoms (ocular MG). Thymectomy gives the best results (seen in 2-5 years) in young adults with MG in the early stages (response is poor in those over 60).
- Assisted ventilation in myasthenia crisis.
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Contact your physician if you think your child has this disease. Ask that your physician work closely with other specialists such as neurologists, and remember there is a lot you can do to battle MG. You can also get information by calling the Myasthenia Gravis Foundation at 1-800-541-5454.
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- Botulism (poison produced by bacteria in poorly canned foods)
- ALS (amyotrophic lateral sclerosis)
- Lambert-Eaton syndrome
- Drugs used in anesthesia or aminoglycosides
- Polymyositis
- Other neuropathies such as multiple sclerosis
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