What is 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

Lambert-Eaton myasthenic syndrome (LEMS) is a rare presynaptic disorder of neuromuscular transmission in which quantal release of acetylcholine (ACh) is impaired, causing a unique set of clinical characteristics, which include proximal muscle weakness, depressed tendon reflexes, posttetanic potentiation, and autonomic changes. [1] The initial presentation can be similar to that of myasthenia gravis (MG), but the progressions of the 2 diseases have some important differences.

LEMS disrupts the normally reliable neurotransmission at the neuromuscular junction (NMJ). This disruption is thought to result from an autoantibody-mediated removal of a subset of the P/Q-type Ca2+ channels involved with neurotransmitter release. [2]

In 40% of patients with LEMS, cancer is present when the weakness begins or is found later. This is usually a small cell lung cancer (SCLC), although LEMS has also been associated with non-SCLC, lymphosarcoma, malignant thymoma, or carcinoma of the breast, stomach, colon, prostate, bladder, kidney, or gallbladder. [2]

Clinical manifestations frequently precede cancer identification. In most cases, the cancer is discovered within the first 2 years after onset of LEMS and, in virtually all cases, within 4 years.


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