Myasthenia gravis is a chronic, autoimmune, neuromuscular condition that causes muscle weakness in different parts of the body. While those with ocular myasthenia typically experience weakness in only the eye muscles (ocular means relating to the eye), those with generalized myasthenia gravis have a more severe form of the disease and may experience weakness in other muscle groups.
What causes generalized myasthenia gravis?
An autoimmune condition means that the immune system mistakenly attacks and destroys the body’s own tissues by forming autoantibodies. Antibodies are a natural part of the immune system and usually attack foreign invaders such as bacteria or viruses.
In myasthenia gravis, autoantibodies attack acetylcholine receptors, which are essential in facilitating muscle contraction and movement.
Symptoms of generalized myasthenia gravis
A hallmark of this disease is increasing muscle weakness as the muscle gets used, with the weakness resolving with rest. So, muscle weakness is usually better in the morning and worsens as the day goes on.
The muscles of the eye often are affected first and patients may develop droopy eyelids and double vision. Generalized myasthenia gravis develops in about 50 to 80 percent of those who develop eye symptoms, with patients gradually experiencing difficulty speaking (dysarthria), problems chewing and swallowing (dysphagia), and trouble performing everyday tasks, such as combing hair or climbing stairs, caused by weakness in the arm and leg muscles.
Patients may appear to be expressionless because the condition may cause facial muscle weakness. Nearly all patients who eventually develop generalized myasthenia gravis do so within two or three years of first displaying symptoms.
Sudden, severe weakening of the muscles involved in breathing results in a myasthenic crisis, a serious, life-threatening condition that is commonly provoked by an infection, undergoing surgery, or pregnancy. Patients with myasthenic crisis often require emergency care.
Who gets generalized myasthenia gravis?
Women are more likely than men to get generalized myasthenia. The condition also usually affects women at a younger age (before the age of 40), while men are more likely to develop it after the age of 60.
Myasthenia gravis often develops in those with no family history of the condition. However, 3 to 5 percent of patients may have family members who have the same disease or other autoimmune disorders. This suggests that variations in genetic components, specifically in the human leukocyte antigens (proteins that have an important role in the immune system) may influence the risk of developing myasthenia gravis.
Myasthenia gravis is diagnosed with blood samples that are checked for the presence of autoantibodies. About 40 percent of people with generalized myasthenia gravis may not have autoantibodies for acetylcholine receptors, but instead have autoantibodies against other important components that allow muscle movement.
Treatment and prognosis of generalized myasthenia gravis
People with ocular and generalized myasthenia gravis are treated with similar medications to control symptoms. In 2017, the U.S. Food and Drug Administration (FDA) approved Soliris (eculizumab) for the treatment of generalized myasthenia gravis. The approval is for those patients who have acetylcholine receptor antibodies.
Additionally, patients with generalized myasthenia gravis tend to benefit more from surgical removal of the thymus (thymectomy) compared to those with ocular myasthenia gravis.
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