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Myasthenia Gravis

Definition


Disease: Myasthenia Gravis Myasthenia Gravis
Category: Immune diseases
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Disease Definition:

Weakness and fatigue of any of the muscles under one's voluntary control characterize myasthenia gravis. A breakdown in the normal communication between nerves and muscles is the cause of myasthenia gravis.

Signs and symptoms such as drooping eyelids, double vision, weakness of arm or leg muscles, and difficulties with breathing, swallowing, chewing and speech may be relieved by treatment, though there is no cure for myasthenia.

Myasthenia gravis is more common in men older than 60 and in women younger than 40, however, it can affect people of any age. Myasthenia gravis occurs in 1 or 2 people per 10,000.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

As the affected muscle is used repeatedly, muscle weakness caused by myasthenia gravis worsens. The muscle weakness may come and go since symptoms typically improve with rest. Certain muscle groups are more commonly affected than others, while myasthenia gravis can affect any of the muscles that a person controls voluntarily.

ARM AND LEG MUSCLES:
Usually in conjunction with muscle weakness in other parts of the body such as throat, face or eyes, myasthenia gravis can cause weakness in the legs and arms. Arms are more affected by the disorder than the legs. However, one may waddle when he/she walks if the disease affects his/her legs.  

EYE MUSCLES:
The first signs and symptoms of this disease involve eye problems in more than half the people who develop myasthenia:

 

  • Blurred vision, which may come and go
  • Drooping of one or both eyelids (ptosis)
  • Double vision (diplopia), which may be horizontal or vertical


FACE AND THROAT MUSCLES:
The first symptoms involve face and throat muscles in about 15% of people with myasthenia gravis, which can cause difficulties with the following:

Speaking:
Depending upon which muscles have been affected, one's speech may be very soft or it may sound nasal.

Swallowing:
It may be difficult to eat, drink or take pills because one may choke very easily. Liquids one is trying to swallow may also come out his/her nose in some cases.

Chewing:
If one has been eating something hard to chew in particular, such as steak, the muscles used for chewing may wear out halfway through a meal.

Facial expression:
If the muscles that control the facial expressions are affected, family members may note that one has "lost the smile".

In case a person has problems with chewing, breathing, walking, swallowing and seeing, he/she should talk to a doctor.
 

Causes:

By releasing chemicals called neurotransmitters, which fit precisely into receptor sites on the muscle cells, the nerves communicate with the muscles. Antibodies that block or destroy many of the muscles' receptor sites for a neurotransmitter called acetylcholine are produced by the immune system in myasthenia gravis. Weakness may result because when there are fewer receptor sites available, the muscles receive fewer nerve signals.

It's thought that the production of these antibodies may be maintained or triggered by the thymus gland, which is a part of the immune system located in the upper chest beneath the breastbone. Small in healthy adults, the thymus is large in infancy. However, the thymus is abnormally large in some adults with myasthenia gravis. Thymus gland tumors that some people have are usually noncancerous.

 Myasthenia gravis can worse due to the following factors:

 

  • Stress
  • Some medications such as quinine, calcium channel blockers, beta blockers and some antibiotics
  • Fatigue
  • Extreme heat
  • Illness

Complications

Complications:

Some of the complications of myasthenia gravis can be life-threatening, although the complications are treatable in general.

MYASTHENIC CRISIS:
When the muscles that control breathing become too weak to do their jobs, a life-threatening condition called myasthenic crisis occurs. Blood-filtering therapies and medications help people recover from myasthenic crisis, so they can start breathing on their own again. To provide mechanical assistance with breathing, emergency treatment is needed.

THYMUS TUMORS:
A tumor in the thymus, a gland under the breastbone that is involved with the immune system, is found in about 15% of the people who have myasthenia gravis. Most of these tumors are noncancerous.

OTHER DISORDERS:
The following problems are more likely to happen to people who have myasthenia gravis:

Rheumatoid Arthritis:
Problems with the immune system cause this type of arthritis. It can result in joint deformities that make it difficult to use the hands, and it is most conspicuous in the wrists and fingers.

Underactive or Overactive Thyroid:
Hormones that regulate the metabolism are secreted by the thyroid gland, which is located in the neck. The body uses energy more slowly if the thyroid is underactive. And it uses energy too quickly if the thyroid is overactive.

Lupus:
The disease in which the immune system attacks certain parts of the body is called lupus. A red rash on the face, extreme fatigue, hair loss and painful or swollen joints are common symptoms of this condition.

Treatments:

To relieve symptoms of myasthenia gravis, a variety of treatments is used either alone or in combination.

MEDICATIONS:

Immunosuppressants:
Medications that alter the immune system, such as mycophenolate, cyclosporine or azathioprine may be prescribed.

Cholinesterase inhibitors:
The communication between nerves and muscles is enhanced by drugs such as pyridostigmine. These drugs improve muscle strength and muscle contraction, though they don't cure the underlying problem.

Corticosteroids:
Limiting antibody production, these types of drug inhibit the immune system. However, serious side effects such as increased risk of some infections, bone thinning, diabetes, weight gain and an increase and redistribution of body fat may be caused by prolonged use of corticosteroids.

THERAPY:

Plasmapheresis:
A filtering process similar to dialysis is used in this procedure. The antibodies that are blocking transmission of signals from the nerve endings to the muscles' receptor sites are removed by a machine that the blood is routed through. However, the beneficial effects usually last only a few weeks.

Intravenous immune globulin:
The body is supplied with normal antibodies that alter the immune system response in this therapy. The benefits usually last less than a month or two and it can take a week or two to start working, though it has a lower risk of side effects than do plasmapheresis and immune-suppressing therapy.

SURGERY:

There is a tumor in the thymus which is a gland under the breastbone that is involved with the immune system in about 15% of the people who have myasthenia gravis. A person will need to have the thymus removed when having such a tumor.

It's unclear whether the potential benefit of removing the thymus outweighs the risks of surgery for people with myasthenia gravis who don't have a tumor in the thymus. It is an individualized decision between the patient and the doctor, however, surgery is not recommended if:

 

  • The patient is over 60 years old
  • The symptoms involve only the eyes
  • The symptoms are mild

Prognosis:

Not Available

Expert's opinion

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