Types of Myasthenia Gravis That Involve an Autoimmune Response
Drug-Related Myasthenia Gravis:
There have been many instances in which a patient has experienced an onset of myasthenia gravis during penicillamine treatment for diseases such as rheumatoid arthritis. This disease onset may be caused by an alteration in the immune system, which allows for the production of anti-AChR antibodies due to the effects of the drug. Aside from penicillamine, several other drugs can heighten the symptoms of myasthenia gravis in patients that already have the disease. Therefore, even small doses of any drug that acts as a neuromuscular blocking agent should be avoided by patients with myasthenia gravis.
Viral/Bacterial Myasthenia Gravis:
Some forms of myasthenia gravis seem to have been brought on by some sort of bacteria or viral infection, with the patients developing some symptoms of myasthenia gravis shortly afterward. The explanation for this seems to be the theory of molecular mimicry, where the protein amino acid sequence of the foreign invader is similiar to the same sequence of a sequence in the body. The immune system now recognizes both the foreign and the new "self" molecule as foreign. In the case of myasthenia gravis, there is evidence that herpes simplex is similar enough to initiate an immune response against protein components of the acetylcholine receptors.
Transient Neonatal Myasthenia Gravis:
Neonatal myasthenia gravis, which occurs in infants born to myasthenic mothers, is due to the transplacental exchange of pathogenic immunoglobulins, with or without AChR antibodies, from mother to infant. This disease occurs in about only 12% of all children born to myasthenic mothers, but anti-AChR antibodies can be found in most. The infant's symptoms are generally exposed by the third day of life, and without immediate treatment, the myasthenic symptoms may gradually subside over 1-4 weeks. The disease becomes permanent when there is irreversible destruction of AChR by the maternal antibodies, or production of antibodies by the infant; this only occurs on rare occasions. Although this disease is passed along from the mother, there is no relation between the degree of weakness in the infant and the degree of weakness in the mother.
Adult-Onset Myasthenia Gravis:
This form of myasthenia gravis usually begins in the third decade of life for women, and the fifth decade for men. This form carries with it all of the symptoms that are normally found in patients with myasthenia gravis. The disease will generally reach its greatest severity within the first three years after onset. Myasthenia gravis may coexist with other autoimmune diseases, and thyroid disease may heighten the myasthenic signs and symptoms.
Experimental Autoimmune Myasthenia Gravis:
This disease model of myasthenia gravis was originally induced in rabbits immunized with AChR from the eel's electric organ. Experimental myasthenia gravis can also be induced by introduction of AChR from many different species, or peptide fragments of the AChR. This disease is divided into an acute and a chronic phase. The acute phase is much like human myasthenia gravis. Two weeks after injecting rats with the immune cells, damage to junctional folds can be seen. Damage to the folds can lead to postsynaptic fragments in the synaptic cleft and the presence of macrophages within the neuromuscular junction. There is quite a bit of literature on this disease, as it is helping to provide information about the treatment of human myasthenia gravis.
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