What causes Lambert-Eaton myasthenic syndrome (LEMS)?

Updated: May 23, 2019
  • Author: David E Stickler, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

For many years, clinical observations suggested an autoimmune etiology for LEMS. Such observations included the following:

  • LEMS is frequently associated with known autoimmune diseases

  • Prednisone, plasma exchange (PEX), and intravenous immunoglobulin (IVIg) are effective treatments

  • Patients with LEMS but without cancer frequently have elevated serum levels of organ-specific autoantibodies

More direct evidence has been accumulated supporting the autoimmune etiology of LEMS. Active zone particles (AZPs), which represent the VGCCs, are normally arranged in regular parallel arrays on the presynaptic muscle membrane. In patients with LEMS and in mice injected with LEMS immunoglobulin G (IgG), divalent antibodies against the VGCC cross-link the calcium channels, disrupting the parallel arrays. Ultimately, the AZPs cluster and decrease in number.


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