Eaton-Lambert myasthenic syndrome (ELMS) is an autoimmune disease in which autoantibodies attack the voltage-gated calcium channels (VGCC), thus interfering with the release of acetylcholine at the presynaptic motor nerve terminal. Eaton-Lambert myasthenic syndrome is also known as Lambert-Eaton myasthenic syndrome.

The most recent “best” estimate for the occurrence of ELMS is 1:100,000.

Patients diagnosed with ELMS usually have some form of cancer, whether or not it has been diagnosed. Clinical manifestations of ELMS typically precede the identification of the form of cancer present. Usually, the cancer is identified within 2 years of the ELMS diagnosis. Evidence accumulating over recent years indicates that active zone particles (AZPs) represent the VGCC and align in regular parallel arrays along the presynaptic muscle membrane. In ELMS patients, divalent antibodies act on the VGCCs, cross-linking these gates and causing disruption of the parallel arrays. This disruption causes AZPs to cluster and ultimately decrease. The process culminates in the characteristic weakness of this disorder.