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Myasthenia Gravis
Sunday, 18 January 2004
Sunday, 18 January 2004

What

Myasthenia gravis is a neurological disorder that causes weakness by affecting the way nerves communicate with muscles. The connection between the nerve and the muscle is called the neuromuscular junction and is a small space where chemical messengers deliver signals from the nerves to the muscles to tell them to contract. In myasthenia gravis the body’s immune system disturbs this communication, causing weakness that worsens with the use of the muscle.

Who

Myasthenia gravis occurs in all ethnic groups, and the incidence of the disease is about 14 in 100,000 in the U.S. Females tend to be affected more when the disease presents before the age of 40. The most common age of onset of symptoms is in the teens and 20’s for women and the 60’s and 70’s for men. Rarely, children can be affected by the disorder.

Signs and Symptoms

The first signs of the disease are usually weakness of the muscles controlling the eye (extraocular muscles), drooping eyelids, and double vision. Sometimes children with myasthenia gravis also experience generalized weakness. Later in the progression of the disease, children have difficulty chewing, swallowing, and talking due to weakness of the muscles in the throat. One of the most serious symptoms is difficulty breathing due to weakness of the muscles involved in respiration. Typically, the weakness fluctuates throughout the day with it being least problematic in the morning and worsening as the day progresses. Characteristically, the weakness is made much worse by exercise and improves with rest.

Possible Causes

Myasthenia gravis is caused by antibodies to the acetylcholine receptors (AChR), the main chemical messengers used at the neuromuscular junction. Antibodies are part of the body’s normal defense mechanism to attack foreign molecules and organisms. However, problems can occur when the body has antibodies to its own cells. This is referred to as an autoimmune disease. The antibodies against the AChR in myasthenia gravis increasingly destroy the receptors and also cause direct injury to the membrane on which the receptors are located. Since the AChR is needed to receive the acetylcholine signal from the brain telling the muscle to contract, the functioning of the muscle is impaired when the receptors are destroyed.

Diagnosis

The diagnosis of myasthenia gravis is usually based on tests that show the abnormal function of the neuromuscular junction. Diagnosis is strengthened when there is improvement with specific medications for the disease called acetylcholinesterase inhibitors, which prevent the destruction of the acetylcholine signal, thus improving muscle strength. The presence of antibodies against the AChR complex can often be detected by a blood test, but this may be less reliable in children since 20% do not have detectable levels of these antibodies.

Treatment

The treatment for myasthenia gravis varies for individuals. Acetylcholinesterase inhibitors, such as pyridostigmine, are recommended as the sole treatment for young children. Other treatment options include corticosteroids such as prednisone, immunosuppressive medications, and plasma exchange, which are typically used as short-term therapy for patients with worsening symptoms. The adverse effects of plasma exchange include nausea, lightheadedness, chills, and cardiac arrhythmia. Individuals with myasthenia gravis also often have involvement of the thymus gland. Excessive growth of the thymus occurs in 65% of individuals with myasthenia gravis, and thymoma (tumor of the thymus) occurs in 15%. Therefore, it is important to screen for these conditions and perform a thymectomy (removal of the thymus) if necessary.

Prognosis

The prognosis for myasthenia gravis is generally very good, but continual medication and therapy is needed. Approximately 95% of individuals survive beyond 5 years. The prognosis in children is usually better than adults since the rate of spontaneous remission is high and the disease is often milder.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Myasthenia Gravis Foundation of America
Great summary of the disease with details on diagnostic tests and treatments. Newsletter is available.

The Myasthenia Gravis Association
Very simple and concise summary for parents. Newsletter is available.

National Institute of Neurological Disorders and Stroke
Brief summary of information. Also has a fact sheet with more information.

Google Search for Myasthenia Gravis

References and Sources

Cotran R, Kumar V & Collins T (1999). Robbins Pathologic Basis of Disease, 6th ed. WB Saunders, p 1289. Howard, James (2003). Rakel: Conn’s Current Therapy, 55th ed. p. 1007-1016. www.home.mdconsult.com/das/book/33965647-2/view/1085/1285.html/top Engel, Andrew (2000). Goldman: Cecil Textbook of Medicine, 21st ed. WB Saunders Company. www.home.mdconsult.com/das/book/33965647-2/view/882/561.html/top