Myasthenia gravis (MG) is a chronic autoimmune neuromuscular condition that causes muscle weakness in different parts of the body. While patients with ocular MG typically experience weakness only in the eye muscles, those with generalized MG have a more severe form of the disease and may experience weakness in other muscle groups.
Generalized MG usually affects more women than men, and particularly those of a younger age (under age 40). Men are more likely to develop the condition after the age of 60.
Causes
MG is an autoimmune condition caused by the production of self-reactive antibodies that attack and damage acetylcholine receptors, which are essential in facilitating muscle contraction and movement.
However, about 15% of people with generalized MG do not have antibodies targeting acetylcholine receptors. Instead, these patients have self-reactive antibodies directed against other important molecules involved in nerve-muscle communication, such as the protein muscle-specific kinase (MuSK).
MG often develops in those with no family history of the condition. However, 3–5% of patients may have family members who have the same disease or other autoimmune disorders. This suggests that variations in genetic components, specifically in human leukocyte antigens — proteins that have an important role in the immune system — may influence the risk of developing MG, including its generalized form.
Symptoms
A hallmark feature of MG is increasing muscle weakness with repetitive movements that tend to ease with rest.
Often, eye muscles are the first to be affected, causing patients to develop double vision and eyelid droopiness. Generalized MG develops in about 50–80% of those who develop eye symptoms, with patients gradually experiencing difficulty speaking (dysarthria), with slow or slurred speech, problems chewing and swallowing (dysphagia), and trouble performing everyday tasks, such as combing their hair or climbing stairs.
Nearly all patients who eventually develop generalized MG do so within two or three years of first displaying symptoms.
Sudden severe weakening of the muscles involved in breathing may cause patients to undergo a myasthenic crisis, a serious, life-threatening condition that is commonly triggered by an infection, surgery, or pregnancy. Patients with myasthenic crises often require emergency care.
Treatment and prognosis
In most MG patients, treatments can significantly ease muscle weakness and enable them to lead to a normal or nearly normal life.
Soliris (eculizumab), given as an intravenous (into-the-vein) infusion, was approved by the U.S. Food and Drug Administration in 2017 for the treatment of patients with generalized MG who have acetylcholine receptor antibodies. More recently, Soliris also was found to be safe and effective in individuals with hard-to-treat generalized MG who failed to respond to other therapies.
Immunosuppressants also were found to reduce the risk of progression to generalized MG in patients with ocular MG, a recent study reported.
Additionally, it was found that patients with generalized MG tend to benefit more from thymectomy — a surgical procedure in which the thymus, an organ that is part of the immune system, is removed — compared with those with ocular MG.
In about 50% of the patients undergoing thymectomy, this procedure led to a stable, long-lasting reduction in disease severity. However, a study recently showed that people with generalized MG who have other diseases, or comorbidities, have a worse prognosis and are less likely to go into remission after thymectomy.
Last updated: Nov. 4, 2021
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