Lambert-Eaton Myasthenic Syndrome

Unknown true incidence. Few studies of very specific regions outside USA report prevalence between 0.48 and 3.42 per million.

60–84% of LEMS patients have SCLC.

LEMS mostly affects middle-aged adults, with rare occurrence in children.

Increased risk for fall when ambulating, due to proximal lower extremities weakness

Hypotension due to autonomic dysfunction

Prolonged emergence secondary to persistent muscle weakness

Respiratory compromise or collapse after extubation

Failing extubation, necessitating unplanned ICU admission.

Exacerbation of muscle weakness postoperatively.

Concomitant presence of SCLC may complicate respiratory function.

Autoimmune disorder affecting the presynaptic NMJ.

Most patients present with slow progressive lower extremities muscle weakness.

LEMS is different from MG:

• LEMS affects the proximal lower extremities more than MG.

• Primarily affects presynaptic mechanisms, whereas MG primarily affects postsynaptic mechanisms.

• Muscle weakness transiently resolves with activities in LEMS.

• LEMS is strongly associated with SCLC.

Pathophysiology: Antibodies attack VGCC, diminishing the release of calcium and subsequent reduction in the release of acetylcholine in the presynapse.

LEMS is an autoimmune disease. IgG antibodies target the P/Q type VGCC at the presynaptic endplate of the NMJ.

The strong prevalence of SCLC in patients with LEMS suggests the presence of the same antigen in SCLC and at the presynaptic NMJ.

Cerebellar degeneration may be present in some patients with LEMS. This is likely due to the presence of the P/Q type VGCC in the cerebellum.

Acetylcholine is necessary for the autonomic function and its reduction in LEMS may result in autonomic nervous system dysfunction.