Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by weakness in the muscles that worsens after activity and improves after rest. Affected muscles include those of the eyes, face, throat, neck, and limbs. Common early symptoms of myasthenia gravis include:
- Drooping of one or both eyelids
- Blurred or double vision
- Difficulty swallowing
- Changes in facial expression
- Impaired speech
- Difficulty chewing
- Shortness of breath
- Trouble walking
- Difficulty moving the neck or holding up the head
- Weakness in the arms, hands, fingers, and legs
In rare cases, severe weakness involved in the disorder may cause respiratory failure, a medical emergency. Approximately 15%-20% percent of people with myasthenia gravis experience at least one myasthenic crisis that may be triggered by infection, stress, surgery, or an adverse reaction to certain medications.
What causes myasthenia gravis?
Myasthenia gravis occurs when the immune system produces antibodies to block or destroy receptors for acetylcholine at the neuromuscular junction (where nerve cells connect to the muscles they control), preventing the muscle from contracting.
Antibodies can also block a muscle-specific protein called tyrosine kinase and can impair nerve signal transmission at the neuromuscular junction.
In addition, the thymus gland may play a role in causing the condition, as the gland is responsible for controlling immune function and producing T-lymphocytes or T cells that may attack acetylcholine receptors.
What are risk factors for myasthenia gravis?
Although the disease can occur at any age, it most often affects women ages 20-30 and men ages 60-80. Women of childbearing age are twice as likely than men to develop the condition.
Symptoms may be worsened by:
How is myasthenia gravis diagnosed?
After taking a detailed medical history and performing a physical examination, your doctor may recommend certain tests, including:
- Neurological examination: To check muscle strength and tone, coordination, sense of touch, and eye movements
- Ice pack test: To check if eyelid drooping is improved by ice application
- Blood test: To check levels of acetylcholine receptor antibodies and anti-muscle-specific kinase antibodies
- Edrophonium test: To check ocular (eye) weakness through injections of edrophonium chloride which relieves weakness in people with the condition
- Repetitive nerve stimulation: Involves repeatedly stimulating nerves with small pulses of electricity
- Single fiber electromyography: Detects impaired nerve-to-muscle transmission
- Computed tomography or magnetic resonance imaging: To check if the thymus gland is bigger than usual and rule out other causes
- Pulmonary function test: To measure lung functioning that can help predict respiratory failure
What can be mistaken for myasthenia gravis?
Onset of the disorder may be sudden, and symptoms may not be recognized as myasthenia gravis initially. Disorders that may cause similar symptoms include:
- Generalized fatigue
- Amyotrophic lateral sclerosis (a rare neurological disease that affects the nerve cells responsible for controlling voluntary muscle movement)
- Lambert-Eaton myasthenic syndrome (a rare autoimmune disorder of adulthood characterized by muscle weakness and fatigue, particularly of the hip and thigh muscles)
- Botulism (a serious condition caused by toxins from bacteria called Clostridium botulinum)
- Penicillamine-induced myasthenia
- Congenital myasthenic syndrome (a result of various mutations in the genes involved in nerve-muscle communication)
How is myasthenia gravis treated?
There is no known cure for myasthenia gravis, but treatment can help control symptoms and allow most individuals to have normal life expectancy with a good quality of life:
- Anticholinesterase medications: Mestinon (pyridostigmine) reduces the breakdown of acetylcholine at the neuromuscular junction and improves nerve signal transmission, thereby increasing muscle strength.
- Monoclonal antibody: Eculizumab can be used for the treatment of generalized myasthenia gravis in adults who test positive for the anti-acetylcholine receptor antibody.
- Immunosuppressive drugs: Prednisone, azathioprine, mycophenolate mofetil, and tacrolimus improve muscle strength by suppressing the production of abnormal antibodies.
- Plasmapheresis and intravenous immunoglobulin: These are used in severe cases of the condition:
- Plasmapheresis: A machine is used to replace harmful antibodies in the plasma.
- Intravenous immunoglobulin: A highly concentrated injection of antibodies that are pooled from healthy donors is given to the patient.
- Thymectomy: This is a procedure in which the thymus gland is surgically removed.
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Myasthenia Gravis Fact Sheet. National Institute of Neurological Disorders and Stroke: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Myasthenia-Gravis-Fact-Sheet
Myasthenia Gravis. Cleveland Clinic: https://my.clevelandclinic.org/health/diseases/17252-myasthenia-gravis-mg
Myasthenia Gravis. NORD: https://rarediseases.org/rare-diseases/myasthenia-gravis/
Myasthenia Gravis. Johns Hopkins Medicine: https://www.hopkinsmedicine.org/health/conditions-and-diseases/myasthenia-gravis
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ambenoniumAmbenonium is a discontinued prescription drug used to treat myasthenia gravis, an autoimmune neuromuscular disease. Ambenonium should be used with caution in people with asthma, Parkinson’s disease, and mechanical intestinal or urinary obstruction. Common side effects of ambenonium include nausea, vomiting, abdominal cramps, diarrhea, excessive salivation, increase in bronchial secretions, excessive watering of eyes (lachrymation), sweating, excessive urination (pollakiuria), urinary urgency, muscle twitches (fasciculation), paralyzed tongue muscles, paralyzed respiratory muscles, difficulty swallowing, difficulty breathing, shortness of breath (dyspnea), and others.
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