Autoimmune in nature, this chronic disorder causes loss of strength in the skeletal muscles. The disease can occur when your immune system erroneously manufactures antibodies that interfere with the normal communication between nerves and muscles.
The muscle weakness that defines myasthenia gravis often worsens after activity and improves following rest. Often but not always, the disorder impacts specific muscles — including those that control breathing, eyelid and eye movement, facial expression, chewing, talking, swallowing and neck and limb movements. Weakness may be present all the time but often comes and goes.
Myasthenia gravis is thought to affect between 32,000 and 60,000 Americans. Myasthenia gravis can occur in both genders, all races and at any age. However, it commonly affects women under 40 and men over 60.
There's no known cure, but current available treatments can control symptoms. Most people with this condition have a normal life expectancy.
Types of myasthenia gravis
The condition has several types:
- Generalized myasthenia gravis is the type that affects between 80 and 90 percent of patients diagnosed with the disease. It's characterized by weakness in the trunk, arms and legs.
- Ocular myasthenia gravis affects about 10 to 15 percent of patients diagnosed with myasthenia gravis. Only the muscles that control eye and eyelid movements are affected.
- Bulbar myasthenia gravis affects speaking and swallowing.
- Congenital myasthenia gravis is a rare form that develops shortly after birth and causes generalized symptoms. Sometimes this does not show up until adulthood. Unlike other forms of myasthenia gravis, congenital myasthenia gravis is caused by genetic mutations and is not autoimmune.
- Transient neonatal myasthenia gravis develops in up to 20 percent of infants born to mothers who have the disease. This type is temporary, caused by the mother's antibodies circulating through the placenta. It can last as long as the mother's antibodies remain in the infant's system, usually a few weeks after birth. After this, the baby will never be affected by the disease.
Primary signs and symptoms of myasthenia gravis
Symptoms you may experience include:
- Drooping of one or both eyelids, called ptosis.
- Blurred or double vision due to weakness of the muscles that control eye movements.
- Weakness in the neck, fingers, hands, arms and legs.
- Impaired speech.
- Difficulty swallowing.
- Shortness of breath.
Diagnosing myasthenia gravis
Your HonorHealth neurologist will perform tests that include the following to diagnose myasthenia gravis:
- A blood test can detect antibodies directed against the acetylcholine receptor in about 85 percent of generalized myasthenia gravis patients (but only 50 percent of ocular patients). This test is very specific.
- There are newer antibodies, other than acetylcholine receptor antibodies, that can cause myasthenia gravis. An anti-MuSK antibody test can be useful for the remaining 15 percent of myasthenia gravis patients who have tested negative for the acetylcholine antibody. About 40 percent of patients with a negative acetylcholine antibody response test positive for the anti-MuSK antibody.
- A test for anti-LRP4 antibodies can help diagnose myasthenia gravis in patients who do not have either acetylcholine receptor or anti-MuSK antibodies.
- A CT scan to look for a chest tumor called thymoma, a benign tumor of the thymus gland, that's present in 10-15 percent of patients with generalized myasthenia gravis.
- Electromyography studies, which along with acetylcholine antibody tests, are the primary tests used to confirm a clinical diagnosis of myasthenia gravis.
Causes and risk factors for myasthenia gravis
Myasthenia gravis causes include:
- Disruption in the transmission of nerve impulses to muscles.
- Blockage, alteration or destruction by antibodies of receptors for the neurotransmitter acetylcholine.
- In some cases a thymoma is responsible.
- Rarely, certain medications can trigger myasthenia gravis.
Treatment options for myasthenia gravis
Treatment from your HonorHealth neurologist can include:
- Medications such as corticosteroids (such as prednisone) and immunosuppressants are often effective in reducing the disease activity.
- Medications called anti-acetylcholinesterase inhibitors that impede an enzyme from breaking down the neurotransmitter acetylcholine and can improve symptoms.
- Plasmapheresis, or plasma exchange, may be useful. This procedure removes abnormal antibodies from blood plasma.
- Intravenous immune globulins that can affect the function or production of abnormal antibodies.
- Eculizumab prevents acetylcholine receptor antibodies from affecting muscle cells. It's administered as an intravenous infusion every two weeks for patients resistant to the other therapies.
- Thymectomy, surgery to remove the thymus gland (whether or not there's a tumor), can increase your chances of going into remission.