Myasthenia gravis is a disease that manifests itself with symptoms of muscle weakness and muscle fatigue. Although this condition usually becomes apparent during adulthood, symptom onset can occur at any age. You can find more information below.
What is myasthenia gravis?
Myasthenia gravis is a chronic disease that causes weakness in the skeletal muscles responsible for breathing and movement parts of the body, including the arms and legs. The Latin and Greek name myasthenia gravis means “severe muscle weakness”.
The hallmark of this disease is muscle weakness that worsens after periods of activity and goes away after periods of rest. Certain muscles are often (but not always) affected by the disease, such as the muscles that control eye and eyelid movement, facial expression, chewing, speech, and swallowing. The muscles that control breathing, neck and limb movements may also be affected.
Current treatments can control symptoms and often allow people to enjoy a relatively high quality of life. Most people with this condition have a normal life expectancy.
Who is it seen in?
Myasthenia gravis affects both men and women and occurs in all racial and ethnic groups. It most commonly affects young adult women (under 40) and older men (over 60), but can occur at any age, including childhood. Myasthenia gravis is not genetic or contagious. However, sometimes the disease can occur in more than one member of the same family.
Although myasthenia gravis is rarely seen in infants, the fetus can receive antibodies from a mother affected by myasthenia gravis (a condition called neonatal myasthenia ). Most of the time in newborn babies this condition is temporary and the child’s symptoms usually disappear within two to three months after birth.
What is myasthenic crisis?
Myasthenic crisis is a medical emergency that occurs when the muscles that control breathing weaken to the point where individuals need a ventilator to breathe. About 15-20 percent of myasthenia patients experience at least one myasthenic crisis. This condition often requires immediate medical attention and can be triggered by infection, stress, surgery, or an adverse reaction to medication.
What causes myasthenia gravis?
Myasthenia gravis is caused by an error in the transmission of nerve impulses to the muscles. Normal communication between nerve and muscle occurs when nerve cells are interrupted at the neuromuscular junction, where they connect with the muscles they control.
Neurotransmitters are chemicals that neurons or brain cells use to transmit information. Normally, when electrical signals or impulses travel down a motor nerve, the nerve endings release a neurotransmitter called acetylcholine. Acetylcholine passes through the nerve ending and binds to acetylcholine receptors on the muscle. Binding of acetylcholine to its receptor activates the muscles and causes muscle movement.
In myasthenia gravis, antibodies (immune proteins) block, replace, or destroy acetylcholine receptors at the neuromuscular junction, which prevent muscle movement. In most people with myasthenia gravis, it is caused by antibodies against the acetylcholine receptor itself. However, antibodies against other proteins such as MuSK protein (Muscle Specific Kinase) can also cause impaired transmission at the neuromuscular junction.
These antibodies are produced by the body’s own immune system. Myasthenia gravis is an autoimmune disease because the immune system, which normally protects the body from foreign organisms, mistakenly attacks itself.
The thymus is a gland that controls immune function and is perhaps associated with myasthenia gravis. The gland, located in the area behind the breastbone, is quite large in children. It grows again until puberty and then shrinks and is replaced by fat. During childhood, the thymus plays an important role in the development of the immune system, as it is responsible for producing T-lymphocytes or T cells , a specific type of white blood cell that protects the body from viruses and infections.
In many adults with myasthenia gravis, the thymus gland remains large. People with the disease typically have a lymphoid hyperplasia -like clump of immune cells in their thymus glands – a condition that usually only occurs in the spleen and lymph nodes during an active immune response. Some individuals with myasthenia gravis develop thymomas (tumors of the thymus gland) . Thymomas are mostly harmless, but they can be cancerous.
The thymus gland plays a role in the development of myasthenia gravis, but its function is not fully understood. Scientists believe that the thymus gland may give false instructions to develop immune cells, eventually causing the immune system to attack its own cells and tissues and produce acetylcholine receptor antibodies, paving the way for neuromuscular transmission attack.
What are the symptoms of myasthenia gravis?
Although myasthenia gravis can affect any skeletal muscle, the muscles that control eye and eyelid movement, facial expression, and swallowing are most affected. The onset of the disorder can be sudden, and the symptoms are often not immediately recognized. In most cases, the first noticeable symptom is weakness of the eye muscles. Difficulty swallowing and speech disorder may also be among the first symptoms. The degree of muscle weakness associated with myasthenia gravis varies widely between individuals, ranging from a regional form limited to the eye muscles ( ocular myasthenia ) to a severe or generalized form in which many muscles – sometimes including those that control breathing – are affected.
Symptoms of myasthenia gravis may include:
- Drooping of one or both eyelids ( ptosis )
- Blurred or double vision ( diplopia ) due to weakness of the muscles that control eye movements
- change in facial expression
- difficulty swallowing
- Shortness of breath
- Speech disorder ( dysarthria )
- Weakness in the arms, hands, fingers, legs, and neck
How is myasthenia gravis diagnosed?
The doctor may order a variety of tests to confirm the diagnosis, including:
- Physical and neurological examination: The doctor will first review the individual’s medical history and perform a physical examination. In the neurological examination, he checks for impaired muscle strength and tone, coordination, sense of touch, and eye movements.
- Tensilon test: This test uses injections of edrophonium chloride to briefly relieve weakness in people with myasthenia gravis . The drug inhibits the breakdown of acetylcholine and temporarily increases acetylcholine levels at the neuromuscular junction. It is often used to test for ocular muscle weakness.
- Blood test: Most individuals with myasthenia gravis have abnormally high levels of acetylcholine receptor antibodies. A second antibody called an anti-MuSK antibody has been found in about half of patients who do not have acetylcholine receptor antibodies, and a blood test can detect this antibody. However, some patients do not have any of these antibodies. These individuals are said to have seronegative (negative antibody) myasthenia.
- Electrodiagnosis: These tests involve repetitive nerve stimulation that repeatedly stimulates a person’s nerves with small electrical pulses to tire certain muscles. Muscle fibers and other neuromuscular disorders in myasthenia gravis do not respond well to repeated electrical stimulation compared to muscles from normal individuals. Considered the most sensitive test for myasthenia gravis, single fiber electromyography (EMG) detects impaired neuromuscular transmission. EMG can be very helpful in diagnosing mild cases of myasthenia gravis when other tests show no abnormalities.
- Diagnostic imaging: Diagnostic imaging of the chest using computed tomography (CT) or magnetic resonance imaging (emar) can identify the presence of thymoma.
Because weakness is a common symptom of many other disorders, the diagnosis of myasthenia gravis is often missed or delayed (sometimes up to two years) in people who experience mild weakness or whose weakness is limited to just a few muscles.
How is myasthenia gravis treated?
1. Thymectomy treatment
This procedure to remove the thymus gland (which is often abnormal in patients with myasthenia gravis) can reduce symptoms and possibly improve some people by rebalancing the immune system. A scientific study , the study found that thymectomy is helpful for both those with thymoma and those without evidence of tumors.
2. Anticholinesterase drugs
Medications used to treat myasthenia include anticholinesterase agents such as mestinone or pyridostigmine, which slow the breakdown of acetylcholine at the neuromuscular junction, thereby increasing neuromuscular transmission and increasing muscle strength.
3. Immunosuppressive drugs
These drugs increase muscle strength by suppressing the production of abnormal antibodies. These include prednisone, azathioprine, mycophenolate mofetil, tacrolimus, and rituximab. Medications can cause significant side effects and should be carefully monitored by a doctor.
4. Plasmapheresis and intravenous immunoglobulin
These treatments may be an option in severe cases of myasthenia gravis. Individuals may have antibodies in their plasma that attack the neuromuscular junction. These treatments remove destructive antibodies, but their effectiveness usually only lasts a few weeks to months.