Lambert Eaton myasthenic syndrome

Last reviewed 01/2018

Lambert-Eaton myasthenia is a presynaptic myasthenic syndrome characterised by impaired release of acetycholine from nerve terminals.

• Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular junction disorder characterized by fluctuating proximal limb muscle weakness, decreased deep-tendon reflexes, and various autonomic symptoms
  • most frequently associated with small-cell lung cancer (SCLC)
    • 60% of patients have small cell lung carcinoma.
  • aetiology of LEMS is the reduced exocytosis of acetylcholine from nerve endings by antibodies against voltage-gated calcium channels (VGCC-abs)
    • increases in the titers of which are observed in more than 90% of patients with LEMS
  • been reported that titer of muscle anti-acetylcholine-receptor-binding antibodies (AChR-abs), which are more specific for myasthenia gravis (MG), is also increased in a small percentage of patients with LEMS (7%)

The usual age of onset in between 50 and 60 years of age. Men are affected more than women.

Electromyography shows increased evoked potentials after repeated galvanic stimulation (the opposite occurs in myasthenia gravis).

The autoimmune aetiology of Eaton-Lambert should be compared and contrasted with myasthenia gravis.

Reference:

• Newsom-Davis, J. Myasthenia gravis and the Lambert-Eaton myasthenic syndrome. Prescribers' Journal 1993;33(5): 205-11.
• Harper CM, Jr, Lennon VA. Lambert-Eaton syndrome. In: Kaminski HJ, editor. Myasthenia Gravis and Related Disorders. 2nd ed. New York: Humana Press; 2009. pp. 209-225.