Aetiology

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.

Neonatal myasthenia may result from the antibody being passively transferred to a foetus 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.

Reference:

1. Sanders DB, Wolfe GI, Benatar M, et al. International consensus guidance for management of myasthenia gravis: executive summary. Neurology. 2016 Jul 26;87(4):419-25.
2. Ruff RL, Lisak RP. Nature and action of antibodies in myasthenia gravis. Neurol Clin. 2018 May;36(2):275-91.