A Simple Guide to Myasthenia Gravis

A Simple Guide to Myasthenia Gravis
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What is myasthenia gravis?
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Myasthenia gravis is a rare chronic autoimmune neuromuscular disease that cause weakening of the skeletal muscles of the body.
The name myasthenia gravis literally means grave muscle weakness.

What causes myasthenia gravis?
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Myasthenia gravis interferes in the transmission of nerve impulses to muscles. Normally the nerve endings release a neurotransmitter substance called acetylcholine which then travels to the neuromuscular junction. The aceylcholine binds to acetylcholine receptors which are activated and generate a muscle contraction.

In myasthenia gravis, these antibodies block, modify, or destroy the receptors for acetylcholine at the neuromuscular junction and prevents muscle contraction.

In myasthenia gravis, the thymus gland which is responsible for the production of the immune cells is abnormal.
The thymus gland may give incorrect instructions to developing immune cells, ultimately resulting in the production of the acetylcholine receptor antibodies.

Who is at risk of myasthenia gravis?
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Myasthenia gravis occurs at any age usually at age 30-40 in women and 50-60 in men. It occurs more in women than in men.
In rare cases, the foetus may acquire antibodies from a mother affected with myasthenia gravis. Cases of neonatal myasthenia gravis are temporary and the child's symptoms usually disappear within 2-3 months after birth.

Myasthenia gravis is not directly inherited.
Rarely, the disease may occur in more than one member of the same family.

What are the symptoms of myasthenia gravis?
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The typical feature of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest.

The onset of the disorder is usually sudden.

The weakness may affect any voluntary muscle, muscles which control eye and eyelid movement, facial expression, talking, and swallowing,muscles that control breathing, neck and limb movements:
1.weakness of the eye muscles,a drooping of one or both eyelids (ptosis)2.difficulty in swallowing
3.slurred speech
4.blurred or double vision (diplopia) due to weakness of the muscles controlling eye movements,
5.unstable or waddling gait,
6.weakness in arms, hands, fingers, legs, and neck,
7.a change in facial expression,
8.shortness of breath
9.fatigue

How is the diagnosis of myasthenia gravis made?
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The diagnosis of myasthenia gravis involve
1.a complete medical history,

2.physical and neurological examinations,especially for impairment of eye movements or muscle weakness without loss of sensation.

3.blood test to detect the presence of acetylcholine receptor antibodies which are abnormally raised in most patients.

4.the edrophonium response test which requires the intravenous administration of edrophonium chloride or Tensilon(r), a drug that blocks the breakdown of acetylcholine and temporarily increases the levels of acetylcholine at the neuromuscular junction. In people with myasthenia gravis, edrophonium chloride will briefly relieve weakness.

5. Electromyographic studies where repetitive nerve stimulation records weakening muscle responses.

6.Computed tomography may be used to identify an abnormal thymus gland or the presence of a thymoma.

7.pulmonary function testing helps to detect abnormal respiratory function which may fail and lead to a myasthenic crisis.

8.A curare test is now rarely done

How is the treatment for myasthenia gravis ?
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Treatment for myasthenia gravis has improved tremendously with several therapies to help reduce and improve muscle weakness.

1.anticholinesterase agents such as neostigmine and pyridostigmine, which help improve neuromuscular transmission and increase muscle strength.

2.Immunosuppressive drugs such as prednisone, cyclosporine, and azathioprine improve muscle strength by suppressing the production of abnormal antibodies. They must be used cautiously because of their many side effects.

3.Thymectomy, the surgical removal of the thymus gland (usually abnormal in myasthenia gravis), reduces symptoms in more than 70 percent of patients and may cure some individuals, possibly by re-balancing the immune system.

4.plasmapheresis in which abnormal antibodies are removed from the blood, and high-dose intravenous immune globulin, which temporarily modifies the immune system and provides the body with normal antibodies from donated blood.

What are myasthenic crises?
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A myasthenic crisis occurs when the muscles that control breathing weaken to the point that brathing is difficult and requires a respirator for assisted ventilation. It may be triggered by infection, fever, or an adverse reaction to medication.

This condition requires immediate medical attention.

What is the prognosis for myasthenia gravis?
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1.With all these new treatments the prognosis for most patients with myasthenia gravis is good.

2.Many of them will have significant improvement of their muscle weakness.

3.Some cases of myasthenia gravis can go into remission to the extent that medications can be discontinued.

4.Thymectomy hsve resulted in many complete remissions.

5.Life expectancy is not lessened by the disorder.