What is Myaesthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease characterised by varying degrees of weakness of the skeletal muscles in the body. The muscle weakness worsens after activity and improves after rest.

Statistics on Myaesthenia Gravis

The overall incidence is about 4 per million people and the prevalence about 40 per million people.

There are two groups with an increased incidence and a sex association. One is young women with a peak incidence in the third decade and the second is men in the seventh decade.

Risk Factors for Myaesthenia Gravis

The weakness may be exacerbated by pregnancy, decreased potassium, change of climate, emotion, exercise, gentamicin and other drugs.

It is associated with thymic tumour, hypothyroidism, rheumatoid arthritis and SLE.

Progression of Myaesthenia Gravis

It is difficult to predice the course of MG. It is generally though that the course of the illness tends to be defined in the first several years of illness.

Initial symptoms of MG may include difficulty speaking (dysarthria), difficulty swallowing (dysphagia), drooping eyelids (ptosis), and double vision (diplopia). Patients often have nasal-sounding speech and weak neck muscles that give the head a tendency to fall forward or backward. These symptoms occur in about 90% of MG cases, and are usually intermittent (i.e. come and go), they may disappear for weeks and then recur.

Generalized weakness often develops in the trunk, arms, and legs within a year of onset. Usually arm muscles are affected most severely. Muscle weakness tends to worsen as the day progresses, especially after prolonged activity. Pregnancy can improve, worsen, or have little effect on MG symptoms. Frequently, symptoms first occur during pregnancy or after delivery.

Spontaneous remissions without treatment are rare as are drug free remissions following immunosuppressive medication treatment alone. Thymectomy is felt to induce some drug free remissions, however, no controlled trials have been done and none are likely to be done.

Prognosis of Myaesthenia Gravis

Symptoms of myasthenia gravis usually progress to maximum severity within the first few years. After this periods of time, patients usually stabilize or improve. Advances in medical care have greatly reduced the mortality rate from respiratory failure in MG patients.

Patients over the age of 40, those with a short history of severe disease, and those with thymoma have a worse prognosis. In a few cases, MG may cause severe weakness resulting in acute respiratory failure; however, most patients can expect to lead normal or nearly normal lives.

How is Myaesthenia Gravis Treated?

Myasthenia gravis is one of the most treatable neuromuscular disorders. The choice of treatment depends on several factors, including age, overall health, severity of disease, and rate of disease progression.

Therapies include medications such as anticholinesterase agents, prednisone, cyclosporine, and azathioprine; thymectomy, which is the surgical removal of the thymus gland; plasmapheresis, a procedure in which abnormal antibodies are removed from blood plasma; and high-dose intravenous immunoglobulin that modifies the immune system.

A physician will determine which treatment option is best for each patient depending on the severity of the weakness, which muscles are affected, and the patient’s age and other associated medical problems.

Regular follow-up is required for all patients.

Myaesthenia Gravis References

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[2]Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.
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[4] Hurst JW (Editor-in-chief). Medicine for the practicing physician. 4th edition Appleton and Lange 1996.
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[7] McLatchie G and LEaper DJ (editors). Oxford Handbook of Clinical Surgery 2nd Edition. Oxford University Press 2002.
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