Myasthenia Gravis

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Treatment

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.

Medications
Anticholinesterase medications such as neostigmine (Prostigmin®) and pyridostigmine (Mestinon®) are usually prescribed. These drugs prevent ACh destruction and increase the accumulation of ACh at neuromuscular junctions, improving the ability of the muscles to contract.

Side effects include excessive salivation, involuntary muscle twitching (fasciculation), abdominal pain, nausea, and diarrhea. A drug called kaolin may be used with anticholinesterase medications to reduce gastrointestinal side effects.

Corticosteroids (e.g., prednisone) suppress the antibodies that block AChR at the neuromuscular junction and may be used in conjunction with anticholinesterase. Corticosteroids improve symptoms within a few weeks and once improvement stabilizes, the dose is slowly decreased.

A low dosage may be used indefinitely to treat MG; however, side effects such as gastric ulcers, osteoporosis (bone thinning), weight gain, high blood sugar (hyperglycemia), and increased risk for infection may develop over the long term.

Immunosuppressants such as azathioprine (Imuran®) and cyclophosphamide (Neosar®) are used to treat generalized MG when other medications fail to reduce symptoms. Side effects may be severe and include low white blood cell count (leukopenia), liver dysfunction, nausea, vomiting, and hair loss.

Immunosuppressants are not used to treat congenital MG because this condition is not the result of an immune system malfunction.

Other Treatments
Plasmapheresis, or plasma exchange, is used to modify the immune system malfunction. It can be used to treat severe worsening of symptoms (exacerbations) or in preparation for surgery (thymectomy).

In this procedure, blood is removed from the body and blood cells are separated from the liquid portion of the blood (plasma). Then, AChR antibodies are removed and blood cells are diluted with artificial plasma (usually a solution of saline and sterilized human albumin protein) and infused back into the body.

Typically, 2 to 3 liters of plasma is removed and replaced during a single treatment, which takes several hours. Most patients undergo several sessions over the course of 2 weeks or more. Plasmapheresis improves MG symptoms within days and improvement lasts 6–8 weeks.

Risks include low blood pressure, dizziness, blurred vision, and formation of blood clots (thrombosis).

Thymectomy is surgical removal of the thymus gland. It is usually performed on patients with a tumor of the thymus (thymoma) and patients younger than age 55 with generalized MG. Benefits of thymectomy develop gradually and most improvement occurs years after the procedure is performed.

Prognosis

Symptoms of myasthenia gravis usually progress to maximum severity within 3 years. After 3 years, patients usually stabilize or improve. Infants with transient neonatal MG may develop acute respiratory failure within a few weeks after birth.

Advances in medical care have reduced the mortality rate from respiratory failure in MG patients to approximately 3%. Patients over the age of 40, those with a short history of severe disease, and those with thymoma have a worse prognosis.

Prevention

Myasthenia gravis cannot be prevented, but avoiding the following triggers may help patients prevent exacerbations:

• Emotional stress
• Exposure to extreme temperatures
• Fever
• Illness (e.g., respiratory infection, pneumonia, tooth abscess)
• Low levels of potassium in the blood (hypokalemia; caused by diuretics, frequent vomiting)
• Medications (e.g., muscle relaxants, anticonvulsants, certain antibiotics)
• Overexertion

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