What is myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas A Jowkar, MBBS; Chief Editor: Nicholas Lorenzo, MD, CPE, MHCM, FAAPL  more...
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Myasthenia gravis (MG) is a relatively rare autoimmune disorder in which antibodies form against nicotinic acetylcholine (ACh) postsynaptic receptors at the neuromuscular junction (NMJ) of the skeletal muscles. It is a type-II hypersensitivity immune response. The basic pathology is a reduction in the number of ACh receptors (AChRs) at the postsynaptic muscle membrane brought about by an acquired autoimmune reaction producing anti-AChR antibodies.

The reduction in the number of AChRs results in a characteristic pattern of progressively reduced muscle strength with repeated use and recovery of muscle strength after a period of rest. The ocular and bulbar muscles are affected most commonly and most severely, but most patients also develop some degree of fluctuating generalized weakness. [10] The most important aspect of MG in emergency situations is acute worsening of weakness leading to neuromuscular respiratory failure. The diagnosis of myasthenic versus cholinergic crisis and its management is also a significant challenge in emergent settings.

MG is a well-understood and well-managed disease. Pharmacologic therapy includes anticholinesterase agents, such as pyridostigmine, and immunosuppressive agents, such as corticosteroids, azathioprine, mycophenolate mofetil, tacrolimus, sirolimus, cyclosporine, cyclophosphamide, rituximab, plasmapheresis, and intravenous immune globulin (IVIg). Thymectomy has a significant role in the treatment of patients with generalized MG who are positive for acetylcholine receptor antibodies. Thymectomy becomes mandatory if a thymoma is present. Patients with MG require close follow-up care by a neurologist or neuromuscular specialist in cooperation with their primary care physician.

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