Myasthenia gravis an autoimmune disease in which antibodies result in a loss of muscle acetylcholine (ACh) receptors (AChRs). In 85% of cases the antibodies bind to the AChRs themselves ('seropositive') and in the remaining cases (misleadingly described as 'seronegative') the antibodies bind to a different muscle membrane target (1).
Neonatal myasthenia may result from the antibody being passively transferred to a fetus in utero. This condition will be transient.
There are associations between myasthenia gravis and thymic hyperplasia - 75% of cases - and thymoma -15%. Antibodies to striated muscle are usually present in the latter group.
The condition may be exacerbated by drugs, e.g. penicillamine, lithium, aminoglycosides, and phenytoin.
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