Myasthenia gravis (Myasthenia gravis)
Myasthenia gravis is an autoimmune process resulting in weakness of skeletal muscles. Most often, weakness begins in the muscles around the eyes, which can cause ptosis and difficulty in coordinating eye movements, which can lead to blurred or double vision. In one form of the condition known as ocular myasthenia weakness confined to ocular muscles. In most people with myasthenia gravis, however, they may be affected additional muscles in the face and neck. Affected individuals may have unusual facial expressions, difficulty holding his head, dysarthria and / or dysphagia, which can lead to suffocation, nausea and drooling.
Other muscles in the body are also affected in some people with myasthenia gravis, such as the muscles of the arms and legs, making those affected have changes in their way of walking or problems with lifting, rising from a sitting position or climbing stairs. Muscle weakness tends to fluctuate over time, which usually worsens with activity and improves with rest.
The weakness of the muscles of the chest wall and diaphragm can cause breathing problems in some people with myasthenia gravis. About 10 percent of people with this disease suffer a potentially fatal complication in these respiratory muscles weaken to the point that breathing is dangerously impaired, and the affected person requires mechanical ventilation. This respiratory failure, called myasthenic crisis can be triggered by stress, infections or reactions to medications.
People can develop at any age myasthenia gravis. For unknown reasons, it is most often diagnosed in women under 40 and men over 60 years old. It is rare in children, but some newborns of women with myasthenia gravis have signs and symptoms of the disease during the first days or weeks of life. This temporary onset of symptoms called transient neonatal myasthenia gravis.
It is believed that variations in particular genes may increase the risk of myasthenia gravis, but the identity of these genes is unknown. There are many factors that likely contribute to the risk of developing this complex process. Myasthenia gravis is an autoimmune disease that occurs when the malfunction of the immune system attacks self tissues and organs of the body. In myasthenia gravis, immune system interrupts the transmission of nerve impulses to the muscles by producing antibodies to certain proteins to the transmission of nerve signals bind. Antibodies usually foreign particles and germs, marking them for destruction bind, but the antibody in myasthenia gravis attacks normal human protein. In most affected individuals, the antibody to the acetylcholine receptor (AChR) is directed; in others, antibodies attack a related protein called muscle specific kinase (MuSK). In both cases, abnormal antibodies result in a reduction of AChR available. The AChR protein is critical for signaling between nerve and muscle cells, which is necessary for movement. In myasthenia gravis, due to abnormal immune response, is present less AChR, reducing signaling between nerve and muscle cells. These anomalies signaling result in a decrease in muscle movement and muscle weakness characteristic of this disease.
It is not clear the reason for the malfunction of the immune system in people with myasthenia gravis. About 75 percent of affected individuals have an abnormally large thymus and hyperactive. Sometimes tumors (thymoma) that are usually benign develop. However, the relationship between thymus problems and malfunction of the immune system that occurs in myasthenia gravis not well understood. People with myasthenia gravis have a higher risk of developing other autoimmune diseases such as autoimmune thyroid disease and systemic lupus erythematosus. Genetic variations that affect the function of the immune system are likely to affect the risk of developing myasthenia gravis and other autoimmune processes. Some families affected by a hereditary process with similar symptoms of myasthenia gravis, but in which antibodies to AChR or MuSK proteins are not present. This alteration, which is not considered an autoimmune process is called congenital myasthenic syndrome.
In most cases, myasthenia gravis is not inherited and occurs in people with no history of disease in your family. About 3 to 5 percent of affected individuals have other family members with autoimmune myasthenia gravis or other processes, but the pattern of inheritance is unknown.