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

SCLC cells originate from neuroectoderm, share a number of antigens with peripheral nervous system tissue, and contain high concentrations of VGCCs. Calcium influx into these cells is inhibited by LEMS IgG. Antibodies to VGCCs are found in the serum of most LEMS patients. These observations suggest that VGCC antibodies downregulate VGCCs in LEMS.

In patients with LEMS who have SCLC or other cancer, cancer cells presumably contain antigens that mimic VGCCs and induce production of VGCC antibodies. In patients with LEMS but no cancer, VGCC antibodies are probably produced as part of a more general autoimmune state. In patients who have LEMS without cancer, an antibody response to domain IV of the 1A subunit of P/Q-type VGCCs is more common than in patients who have LEMS with cancer.

VGCC antibody levels do not correlate with disease severity among patients with LEMS. However, antibody levels do fall in individual patients if the disease improves after cancer therapy or immunosuppression.

All patients with LEMS who have associated SCLC have a history of long-term smoking. Only half of patients with autoimmune LEMS are long-term smokers.


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