When do patients become symptomatic with myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Patients become symptomatic once the number of AChRs is reduced to approximately 30% of normal. The cholinergic receptors of smooth and cardiac muscle have a different antigenicity than skeletal muscle and usually are not affected by the disease.

The decrease in the number of postsynaptic AChRs is believed to be due to an autoimmune process whereby anti-AChR antibodies are produced and block the AChR. It causes an increase in the turnover of the AChR, and damage of the postsynaptic membrane in a complement-mediated manner.

The exact mechanism of loss of immunologic tolerance to AChR, a self-antigen, is not understood. MG can be considered a B cell–mediated disease, in that it derives from antibodies (a B cell product) against AChR. However, the importance of T cells in the pathogenesis of MG is becoming increasingly apparent. The thymus is the central organ in T cell–mediated immunity, and thymic abnormalities such as thymic hyperplasia or thymoma are well recognized in myasthenic patients.


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