Definition: It is a chronic disorder characterized by weakness and rapid fatigue of any of the muscles under the voluntary.
Myasthenia gravis (MG) is a neuromuscular disorder that causes weakness in the skeletal muscles, which are the muscles that the body uses for movement. It occurs when communication between nerve cells and muscles becomes impaired. The impairment of communication prevents crucial muscle contractions from occurring, resulting in muscle weakness. According to the Myasthenia Gravis Foundation of America, MG is the most common primary disorder of neuromuscular transmission. It is a relatively rare condition that affects between 14 and 20 out of every 100,000 people in the U.S. (Howard, 2006).
MG is a neuromuscular disorder that is usually caused by an autoimmune problem. Autoimmune disorders occur when the immune system mistakenly attacks healthy tissue. In this condition, antibodies (proteins which normally attack foreign, harmful substances in the body) attack the neurotransmitter substance called acetylcholine, which is a crucial substance for nerve cell and muscle communication. This results in the muscle weakness that characterizes the condition.
The exact cause of this autoimmune reaction is unclear to scientists. According to the Muscular Dystrophy Association, it is suspected that there are certain viral or bacterial proteins that may prompt the body to attack acetylcholine (MDA)
The most widely accepted classification of myasthenia gravis is the Myasthenia Gravis Foundation of America Clinical Classification:
• Class I: Any eye muscle weakness, possible ptosis, no other evidence of muscle weakness elsewhere
• Class II: Eye muscle weakness of any severity, mild weakness of other muscles
o Class IIa: Predominantly limb or axial muscles
o Class IIb: Predominantly bulbar and/or respiratory muscles
• Class III: Eye muscle weakness of any severity, moderate weakness of other muscles
o Class IIIa: Predominantly limb or axial muscles
o Class IIIb: Predominantly bulbar and/or respiratory muscles
• Class IV: Eye muscle weakness of any severity, severe weakness of other muscles
o Class IVa: Predominantly limb or axial muscles
o Class IVb: Predominantly bulbar and/or respiratory muscles (Can also include feeding tube without intubation)
• Class V: Intubation needed to maintain airway
The main symptom of MG is weakness in the voluntary skeletal muscles, which are the muscles under your control. This weakness occurs with activity and can get better with rest. The failure of the muscles to contract normally occurs because they cannot respond to the nerve impulse. This is considered to be a blocked communication between nerve and muscle, and without the proper transmission of the impulse, weakness results.
Weakness associated with MG typically gets worse with more activity and improves with rest. Symptoms of MG can include:
• trouble talking
• problems walking up stairs or lifting objects
• facial paralysis
• difficulty breathing because of muscle weakness
• difficulty swallowing or chewing
• hoarse voice
• drooping of eyelid
• double vision
Not everyone will have every symptom, and the degree of muscle weakness can change from day to day. The disease typically progresses over time if left untreated.
According to the National Institutes of Health, MG typically occurs in individuals over the age of 40. Women are more likely to be diagnosed as younger adults, whereas men are more likely to be diagnosed when they are 60 or older (NIH).
Doctor will perform a complete physical exam, as well as take a detailed history of symptoms. He or she will also do a neurological exam. This may consist of:
• checking your reflexes
• looking for muscle weakness
• checking for muscle tone
• making certain your eyes move properly
• testing sensation in different areas of your body
• seeing if you can perform certain movements, like touching your finger to your nose
Other tests that can help your doctor diagnose the condition include:
• repetitive nerve stimulation test
• blood testing for antibodies associated with MG
• edrophonium (Tensilon) test: a drug called Tensilon (or a placebo) is injected, and the patient is asked to perform muscle movements under doctor observation
• imaging of the chest, using CT scans or MRI, to rule out a tumor
There is no cure for MG. The goal of treatment is to manage the symptoms and control the activity of the immune system.
Corticosteroids and immunosuppressants can be used to suppress the immune system. These medications help minimize the abnormal immune response that occurs in MG.
Additionally, cholinesterase inhibitors, such as pyridostigmine (Mestinon), can be used to increase communication between nerves and muscles.
Thymus Gland Removal
Removal of the thymus gland may be appropriate for some patients with MG. The thymus gland is part of the immune system. Once the thymus is removed, patients typically show less muscle weakness.
According to the Myasthenia Gravis Foundation of America, between 10 and 15 percent of people with MG will have a tumor in their thymus (MGFA, 2010). These are always removed, because they may become cancerous.
Plasmapheresis is also known as plasma exchange. This process removes harmful antibodies from the blood. Removing the antibodies causes an improvement in muscle strength.
Plasmapheresis is a short-term treatment. The body continues to produce the antibodies, and weakness may recur. Plasma exchange is helpful before surgery or during times of extreme MG weakness.
There are some things you can do at home to help alleviate symptoms of MG:
• Get plenty of rest to help minimize muscle weakness.
• If you are bothered by double vision, talk to your doctor about whether you should wear an eye patch.
• Avoid stress and heat exposure as both can exacerbate symptoms.
These treatments cannot cure MG. However, treated patients typically see improvements in their symptoms. Some individuals may go into remission, during which treatment is not necessary.
Tell your doctor about any medications or supplements you take. Some drugs can make MG symptoms worse. Before taking any new medication, check with your doctor to ensure it is safe.
Complications of Myasthenia Gravis:
One of the most dangerous potential complications of MG is a myasthenic crisis. This is a life-threatening breathing problem. Talk with your doctor about your risk of a crisis. If you start to have trouble breathing or swallowing, call 911 or go to your local emergency room immediately.
Individuals with MG are at a higher risk of developing other autoimmune disorders, such as lupus and rheumatoid arthritis.