Many drugs and procedures are available for treating MG, each with distinct advantages and disadvantages. Drugs known as cholinesterase inhibitors provide relief from symptoms by blocking the action of acetylcholinesterase and increasing the amount of acetylcholine at the neuromuscular junction. (For a more detailed explanation of how these drugs work, see Causes/Inheritance.)
Immunosuppressant drugs can be used to attack the disease at its source, but they increase susceptibility to infectious diseases and most of them carry other potentially serious side effects.
The benefits and risks of these treatments must be weighed against each other and the needs of the patient. Your doctor or MDA clinic director can help you determine which treatments are appropriate for you.
These drugs, also known as anticholinesterases, have been used against MG since the early 1990s, and can produce relief from symptoms within minutes. The one most commonly used is pyridostigmine (Mestinon).
Cholinesterase inhibitors boost ACh levels not only at the neuromuscular junction but also in the autonomic nervous system (which controls involuntary bodily functions). Sometimes the drugs can cause diarrhea, abdominal cramps and/or excessive saliva. To minimize these side effects, your physician might lower the dose of cholinesterase inhibitors or prescribe atropine, which blocks the ACh receptors on nerve cells.
In rare cases, cholinesterase inhibitors prove sufficient for managing MG, but most people also require immunosuppression — treatment that restrains the actions of the immune system.
Drug warnings and other concerns
Many prescription drugs can unmask or worsen symptoms of MG. These include:
- muscle relaxants used during surgery
- aminoglycoside and quinolone antibiotics
- cardiac anti-arrhythmics
- local anesthetics
- magnesium salts (including milk of magnesia)
When taking a new prescription drug for the first time, it’s a good idea to consult your doctor about its possible effects on MG. Also, you might want to keep a MedicAlert bracelet or card handy to inform emergency medical personnel that you have MG and that certain drugs can be harmful to you.
Overexertion, emotional stress, infections (from tooth abscesses to the flu), menstruation and pregnancy also can lead to increased weakness in MG.
Corticosteroids. These drugs (which include prednisone and prednisolone) reproduce the actions of corticosteroid hormones, which are made by the cortex (outer layer) of the adrenal gland. They have broad anti-immune and anti-inflammatory effects, making them powerful treatments for MG.
They’re not as fast-acting as cholinesterase inhibitors, but they’re faster than some other immunosuppressants, producing improvement within weeks to months. They’re also relatively inexpensive.
A disadvantage of corticosteroids is that they can produce many side effects — some of them potentially serious — including osteoporosis (weakening of bones), mood disturbances, gastrointestinal problems, weight gain, high blood pressure, cataracts and stunted growth (in children). For many people, these side effects can be managed with other therapies; for example, bisphosphonate drugs can be used to prevent osteoporosis.
For others, corticosteroids are used as a first-line defense against MG, then gradually tapered off, and supplemented or replaced with slower-acting immunosuppressants that have fewer side effects. Most of these other drugs were developed to prevent the rejection of transplanted organs, but have since been co-opted for use against MG and other autoimmune diseases.
Azathioprine (Imuran). This was the first non-steroid immunosuppressant to come into widespread use against MG, in the 1970s. It acts more slowly than corticosteroids, producing improvement after three to six months, and usually has few side effects. Occasionally, however, it can produce serious side effects, including inflammation of the pancreas, liver toxicity, bone marrow suppression and possibly an increased risk of cancer.
Mycophenylate mofetil (CellCept). CellCept is a relatively new immunosuppressant, but so far it’s shown promising results against MG in clinical trials. In two small trials completed in 2001, about 65 percent of MG patients experienced gains in strength or a reduced need for prednisone after taking CellCept for several months.
More recent analyses have shown that some people take longer to respond to the drug, but that nearly 75 percent eventually show improvement, with occasional relatively nonserious side effects such as stomach upset, flulike symptoms, rash and tremor.
Cyclosporine (Neoral, Sandimmune). This is a useful, relatively fast-acting treatment for MG, but it may have side effects including increased blood pressure, abnormal kidney function, unwanted body hair and stomach upset.
Cyclophosphamide (Cytoxan, Neosar). This drug is considered effective against MG, but because it has many potentially serious side effects, it’s often reserved for use only when other drugs fail.
Especially in people with bulbar or respiratory symptoms, MG can sometimes worsen to the point of myasthenic crisis, an extreme episode of weakness that culminates in respiratory failure and the need for mechanical ventilation. In some cases, the respiratory muscles themselves give out, and in others, weakness in the throat muscles causes the airway to collapse.
When MG is properly treated, crisis is very rare. And when crisis does occur, it has a good rate of recovery, thanks to the wide range of treatments for MG and the quality of respiratory care at most hospitals.
Sometimes, myasthenic crisis can occur without warning, but it often has an identifiable trigger, such as fever, respiratory infection, traumatic injury, stress, or one of the drug types mentioned above. If you have MG, you should have these conditions monitored by a physician, and if you experience labored breathing or unusual weakness, you should seek immediate medical attention.
Plasmapheresis and intravenous immunoglobulin (IVIG)
In plasmapheresis, also known as plasma exchange, an intravenous line is used to remove antibodies from the blood. IVIg therapy is essentially an injection of nonspecific antibody (immunoglobulin) that might work by dialing down the immune system’s production of its own antibodies, much as warm air tells a thermostat to stop pumping out heat.
These treatments bring about fast, but short-lived relief from MG, and are mostly used until other medications take effect, prior to surgery or for myasthenic crisis. However, some people receive regular plasmapheresis or IVIg as a supplement to immunosuppressant drugs.
In rare cases, pregnancy appears to trigger the onset of MG. In women who already have MG, pregnancy can cause a worsening of symptoms (usually after birth, but sometimes during the first trimester); an improvement (usually during the first trimester); or no change, with about equal likelihood. These trends aren’t consistent from one pregnancy to the next.
Some medications for MG are safe to use during pregnancy and nursing, but some others aren’t recommended. If you’re planning to become pregnant, you should consult your physician, and if you’re a nursing mother, consult your child’s pediatrician.
Between 10 and 20 percent of babies born to mothers with MG develop transient neonatal MG, probably because the antibodies that cause MG can pass through the placenta. Symptoms (such as feeble cry, feeding difficulties or respiratory weakness) often are detected within hours to days after birth, and decreased movement may be detected inside the womb.
As the name implies, transient neonatal MG is only temporary. Most babies require medication and supportive care, but usually recover completely within two months after birth. Permanent weakness or recurrence of MG later in life is extremely rare.
Thymectomy — surgical removal of the thymus gland — is recommended for thymoma and for most cases of generalized MG. It’s believed to be the only therapy capable of producing long-term, drug-free remission from MG, but most data regarding its use have come from case studies rather than clinical trials.
Thymectomy is estimated to produce remission from MG in about 30 percent of people. It’s also known to increase strength or reduce the need for medication in an additional 50 percent. These improvements may take several months to several years after surgery to occur.
Thymectomy usually has the most favorable outcomes in people who are under age 60 and early in the course of the disease. Because the thymus is required for immune system development, most doctors prefer not to perform the surgery on prepubescent children.
For more about myasthenia gravis management, see: