Definition & Overview
Myasthenia gravis is an autoimmune disease characterized by the weakening of voluntary muscles during activity, but improves with rest. The muscles usually affected are those that control the eyes, eyelids, and facial expressions as well as those that are involved when swallowing, talking, and chewing. The muscles in the neck, limbs, and those that control breathing may also be affected.
Myasthenia gravis affects anybody of any age. However, the condition is more prevalent in women above 40 years old and men above 60. This condition cannot be cured, but the symptoms can be treated so that the patient can live a normal life.
The condition is not common. In fact, in the United States, only about 20 people out of 100,000 are affected with the disease. Myasthenia gravis is not hereditary or contagious, although there have been cases where more than one person in the family was diagnosed with the condition.
Cause of Condition
Myasthenia gravis is caused by an abnormality in the immune system. The brain controls the voluntary muscles by sending nerve impulses. The impulses are sent to the muscle fibers through the nerves. However, the nerve fibers and muscle fibers are not actually connected. There is a space between the nerve ending and the muscle fiber called a neuromuscular junction.
The nerve ending sends a chemical called acetylcholine across the neuromuscular junction to the receptor sites of the muscle fiber. Once the receptor sites receive acetylcholine, the muscles will contract.
However, if a person is affected with myasthenia gravis, an antibody blocks the receptor sites. Thus, the muscle fibers fail to contract and weaken easily. Antibodies are an important part of the immune system and are tasked to destroy harmful bacteria and viruses. Unfortunately, in myasthenia gravis, instead of attacking viruses or bacteria, they attack the receptor sites.
Without acetylcholine the muscles become weak, but they normalize when the brain is no longer sending nerve impulses to activate the muscle fibers, which would mean that the body is at rest.
Not only does myasthenia gravis cause muscle weakness, but complications can also develop. Some of the most common complications are myasthenic crisis, thymus tumours, and underactive or overactive thyroid, and autoimmune conditions.
Myasthenic crisis is characterized by the weakening of the breathing muscles. This condition is life-threatening, thus requires immediate medical attention. Thymus tumours, on the other hand, are growths that develop in the thymus, a gland located under the breastbone. The tumours are usually malignant (non-cancerous).
The primary symptom of myasthenia gravis is muscle weakness. The affected muscles become weaker every time they are activated. However, when the person is at rest, the muscles will usually recover, only to become weak again when they are used.
When the condition affects the eyes or eyelids, it may result in ptosis (droopy eyelids) or double vision. If myasthenia gravis affects the throat and face muscles, the person may display symptoms, such as altered speaking, chewing problems, swallowing problems, or limited facial expressions.
Depending on the affected muscles, the condition can cause weakness in the neck and upper and lower extremities and difficulty walking. It may also prevent the patient from holding his or her head up straight.
If you notice any of these symptoms, you should schedule an appointment with your doctor right away. However, if you find it difficult to breathe, proceed immediately to a hospital’s emergency department or call emergency medical services.
Who to See & Types of Treatment Available
If you experience unexplained muscle weakness, you should see your family doctor right away. However, muscle weakness is a common symptom of many disorders and diseases. In fact, it’s seldom that a doctor would suspect myasthenia gravis immediately. Most patients don’t even receive the correct diagnosis of the condition for quite some time. In some patients, it took two years before the condition was diagnosed correctly and the right form of treatment was given.
When you consult your doctor with a complaint of muscle weakness, the doctor will obtain information about diseases in the family. You will then undergo a physical and neurological examination. If myasthenia gravis is suspected at this stage, the doctor will order blood tests to detect acetylcholine receptor antibodies or immune molecules. You will also undergo several more tests, such as an edrophonium test, single fiber electromyography, CT scan, MRI, or a pulmonary function test.
Once myasthenia gravis is confirmed, the doctor will decide on the best treatment method. The doctor will explain that there is no cure for the disease, but the symptoms can be treated so that you’ll be able to live normally.
Treatment will include a variety of medications, such as anticholinesterase agents and immunosuppressive drugs. Anticholinesterase agents help improve neuromuscular transmission and strengthen the muscles. Meanwhile, immunosuppressive drugs suppress the production of abnormal antibodies.
Individuals with myasthenia gravis typically have an abnormal thymus gland. The doctor will recommend the removal of thymus gland through a procedure called thymectomy to treat the symptoms of the disease.
Treatment may also include therapies, such as plasmapheresis. This therapy involves replacing abnormal antibodies in the blood and replacing them with normal ones obtained from a donor’s blood.
In the treatment of myasthenia gravis, a neurologist is often consulted to determine the degree of weakness that a person is experiencing. Once this has been determined, the attending doctor will be able to determine the best form of treatment. The goal of the treatment is to strengthen the muscles to allow the patient to live a normal life. Treatment will also prevent respiratory failure, a condition that requires emergency medical care.
To this date, the National Institute of Neurological Disorders (NINDS) is continuously conducting research on myasthenia gravis to determine the exact cause of the disease, which can lead to the development of a cure for the condition.
Meriggioli MN, Sanders DB. Disorders of neuromuscular transmission. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC, eds. Bradley’s Neurology in Clinical Practice. 6th ed. Philadelphia, Pa: Elsevier Saunders; 2012:chap 78.
Vincent A, Evoli A. Disorders of neuromuscular transmission. In: Goldman L, Schafer AI, eds. Goldman’s Cecil Medicine. 24th ed. Philadelphia, Pa: Elsevier Saunders; 2011: chap 430.