Myasthenia gravis is a chronic disease that causes tiredness and weakened muscles. This muscle weakness worsens after an effort of the muscles and improves with the rest, which is characteristic of this disease. Its gravity comes from the risk of respiratory accidents.
Definition of myasthenia
The gravis is a disease characterized by weakness and abnormally rapid fatigue of muscles that are under voluntary control of the person.
It is caused by a communication problem between nerves and muscles.
It cannot be cured, but treatment can help relieve signs and symptoms, such as weakness of the arm or leg muscles, double vision, drooping eyelids, and speech or breathing difficulties.
The disease most often affects the coulometer muscles that control the movement of the eye and eyelids, so that the first symptoms observed are an inefficient occlusion of the eyelids and / or blurred or double vision, so-called diplopia .
The causes of myasthenia
Nerves communicate with muscles by releasing chemicals (called neurotransmitters) that attach to receptor sites on muscle cells at the junction between the nerve and the muscle (called the neuromuscular junction).
In myasthenia, the immune system produces antibodies (proteins that are supposed to fight against foreign invaders such as bacteria, viruses or fungi) that mistakenly destroy the receptor sites that are fixed by one of the neurotransmitters called acetylcholine. Since there are fewer receptor sites available, the muscles receive fewer nerve signals, resulting in decreased muscle contraction.
Antibodies can also block the function of a protein called tyrosine kinase located in a muscle. This protein is involved in the formation of the neuromuscular junction. When antibodies block the function of this protein, it can lead to myasthenia.
Some researchers believe that the thymus, an organ involved in the immune system and located behind the sternum, can trigger the production of antibodies that block acetylcholine. In some adults with myasthenia gravis, the thymus is abnormally large. Some people with myasthenia gravis also have thymus tumors.
Some people may have myasthenia that is not caused by antibodies that block acetylcholine or tyrosine kinase. Other antibodies may play a role in the development of this condition.
Who is the most affected?
Myasthenia is more common in women (two for one). Although it affects people of all ages, it is more common among women aged 20 to 40 and men between 50 and 70 years.
Diagnosis of myasthenia
It is necessary to see a doctor if the person has difficulties to:
- Use one of his arms or one of his hands
- Raise his head
- Raise your shoulders
The doctor will examine the symptoms and medical history and will perform a physical examination. The doctor can perform several tests by testing the following:
- Muscular force
- Muscle tone
- Sense of touch and sight
The key sign that highlights the possibility of myasthenia gravis is muscle weakness that improves with rest. Tests to confirm the diagnosis may include:
Test with the Tensilon
Injection of Tensilon (edrophonium) may result in a sudden, albeit temporary, improvement in muscle strength. This is an indication of the presence of myasthenia gravis.
Edrophonium blocks an enzyme that degrades acetylcholine, the neurotransmitter that transmits signals from nerve endings to muscle receptors.
If the patient has a drooping eyelid, the doctor can perform a test with a block of ice it lays on the eyelid. After two minutes, the doctor removes the bag and analyzes the drooping eyelid to see if there are any signs of improvement.
A blood test may reveal the presence of abnormal antibodies that disrupt the receptor sites on the muscles.
The doctor attaches electrodes to the skin on the muscles to be tested and then sends small electrical pulses through the electrodes to measure the nerve’s ability to send a signal to the muscle. In the case of a mysathenia, this ability decreases with fatigue.
The doctor may request CT or MRI to check for a tumor or other abnormality in the thymus.
Pulmonary function test
The doctor can perform tests to assess whether myasthenia gravis affects the patient’s breathing.
Evolution and possible complications
The evolution of myasthenia is irregular and unpredictable. The complications of myasthenia gravis are treatable, but some may put the patient’s life at risk, especially respiratory complications.
Myasthenic crisis is a fatal disease that occurs when the muscles that control breathing become too weak to function. It can occur in case of anxiety attack and agitation. Emergency treatment is necessary to provide mechanical assistance to breathing. Some medications and / or blood filtering help people to breathe without assistance.
About 15% of people with myasthenia gravis have a thymus tumor (lymphoepithelioma). Most of these tumors, called thymomas, are not cancerous (benign). This is why the thymus is usually removed (thymectomy) to prevent the possible spread of cancer.
People with myasthenia gravis are more likely to have the following conditions:
- An overactive or overactive thyroid The thyroid gland, which is in the neck, secretes hormones that regulate the metabolism. If the thyroid is inactive, the person is at risk of a cold or weight gain and other problems. An overactive thyroid can cause feelings of heat, weight loss and other problems.
- Autoimmune diseases. People with myasthenia gravis may be more likely to have autoimmune diseases, such as rheumatoid arthritis or lupus .
How to live with myasthenia gravis?
There are approaches that can help the patient cope with the symptoms of myasthenia gravis:
- Set you’re eating routine. The patient must try to eat when he has strength. He must take the time to chew his food and pause between bites. It is advisable to avoid foods that require more chewing, such as raw fruits or vegetables.
- Secure his house. Install grab bars or ramps where there is a need for support such as the bathroom or stairway. Remove obstacles and remove slippery carpets. Clear pathways, sidewalks and walkways of obstacles or slippery things (leaves, snow and debris).
- Electrical appliances. Use an electrical appliance to save energy (eg use an electric toothbrush).
- Ocular patch. Wear a patch if you have dual vision and are writing, reading, or watching television to reduce eyestrain.
- Planning. Plan daily tasks (housework, shopping, etc.) for purchases when you have the most energy.
- Relaxation. Plan to relax. Stress can indeed worsen the condition of myasthenia.
Symptoms of myasthenia
Muscle weakness caused by myasthenia gravis increases when the affected muscle is repeatedly stressed. Muscle weakness fluctuates because symptoms usually improve with rest. However, symptoms of myasthenia tend to progress over time, usually worsening a few years after the onset of the disease.
There are usually times when the patient notices more symptoms (exacerbation phase), interspersed with periods when symptoms diminish or disappear (remission phase).
The muscles affected by myasthenia
Although myasthenia can affect any voluntarily controlled muscle, some muscle groups are more frequently affected than others.
The muscles of the eyes
In more than half of the cases, the first signs and symptoms of myasthenia gravis are eye problems such as:
- Stop the movement of one or both eyelids (ptosis).
- Double vision (diplopia), which improves or disappears when an eye is closed.
The muscles of the face and throat
In about 15% of cases, the first symptoms of myasthenia gravis involve muscles of the face and throat, which can cause:
- disturbances of phonation. the tone and voice (nasal) are distorted.
- Difficulty swallowing The person can choke very easily when she eats drinks or takes her medication. In some cases, the fluids that the person is trying to swallow may come out through their nose.
- Chewing problems. Used muscles can become fatigued if the person eats something that is difficult to chew (such as a steak).
- Limited facial expressions The person may seem to have “lost a smile. If the muscles that control his facial expression are affected.
Neck and limb muscles
Myasthenia can cause weakness in the muscles of the neck, arms, legs, but also in other parts of the body such as the eyes, face or throat.
Risk factors for Myasthenia
There are factors that can aggravate myasthenia gravis such as:
- another disease;
- the stress;
- certain drugs such as beta-blockers, quinine, phenytoin, some anesthetics and antibiotics;
- genetic factors.
Mothers with myasthenia gravis rarely have children born with myasthenia gravis. Indeed, the antibodies are transferred from the mother’s blood to the baby. However, during the baby’s first weeks of life, the antibodies are removed from the baby’s bloodstream and the baby usually ends up recovering normal muscle tone within two months of birth.
Some children are born with a rare, hereditary form of myasthenia, known as congenital myasthenic syndrome.
How to prevent mysathenia?
There is no preventive treatment of the disease.
Treatment of myasthenia
Doctors use a variety of treatments, alone or in combination, to relieve the symptoms of myasthenia gravis.
- Cholinesterase inhibitors. These drugs (eg neostigmine) improve communication between nerves and muscles by blocking the breakdown of acetylcholine. These medications do not heal, but they can improve contraction and muscle strength. Possible side effects include gastrointestinal disturbances, nausea, excessive salivation and sweating.
- Corticosteroids . Corticosteroids inhibit the immune system, limiting the production of antibodies. They are mainly used in the treatment of ocular myasthenia. Prolonged use of corticosteroids, however, can result in serious side effects, such as bone fragility, weight gain, diabetes, and increased risk of infections.
- Immunosuppressants . These are drugs that alter the immune system. Side effects of immunosuppressive drugs can be serious and include nausea, vomiting, gastrointestinal disturbances, and increased risk of infections, liver damage and kidney damage.
- Plasmapheresis . This procedure uses a filtering process similar to that of dialysis. Blood is delivered through a machine that suppresses antibodies. However, the beneficial effects usually last only a few weeks.
- Immunoglobulin. This therapy provides the body with normal antibodies that enhance the immune system’s response. However, it takes about a week to see the effects, and the benefits usually do not last more than three to six weeks. The side effects are minor.
- Monoclonal antibody . Rituximab is a medicine that is used in some cases of myasthenia gravis.
About 15% of people with myasthenia gravis have a thymus tumor. The doctors will then perform a surgical procedure to eliminate the thymus (thymectomy). If there is no tumor, surgery can still decrease the symptoms of myasthenia gravis. The improvement is most often manifested several months after the intervention.
The choice of treatments depends on several factors such as the age of the patient, the severity of his condition, the type of affected muscles and other co-occurring diseases.
A small study suggests that intramuscular injection of huperzine A maintains muscle strength in myasthenia gravis patients after 10 days of treatment. This effect is similar to that seen with neostigmine (an acetylcholinesterase inhibitor). Further larger studies are needed to confirm these results.