A rare autoimmune disorder of the neuromuscular junction.
Lambert-Eaton myasthenic syndrome (LEMS) occurs either as a paraneoplastic disorder in association with an underlying cancer (CA-LEMS), or without cancer and as part of a more general autoimmune state (NCA-LEMS).
Symptoms include insidious and gradual onset of fatigue, weakness, and a dry mouth.
Clinical findings include proximal muscle weakness in hip girdle and thigh muscles; absent or reduced tendon reflexes that may facilitate after brief exercise; and dilated, poorly reactive pupils.
Serum P/Q-type voltage-gated calcium-channel antibodies are usually present. Electrophysiologic studies usually demonstrate decremental responses to low-frequency repetitive nerve stimulation, and may also exhibit postactivation facilitation of >100%.
Over 40% of LEMS patients have underlying cancer, usually small cell lung cancer. Effective treatment of underlying cancer frequently improves symptoms.
Effective symptomatic and long-term treatment options include agents that augment neuromuscular transmission and immunomodulators. However, many patients have long-term disability due to weakness.
Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of the neuromuscular junction. It may occur as a paraneoplastic disorder in association with cancer (CA-LEMS), usually a small cell carcinoma of the lung, or may also occur without cancer, as part of a more general autoimmune state (NCA-LEMS). In both types, LEMS is characterized by the presence of circulating antibodies against voltage-gated calcium channels; these impair neuromuscular transmission by inhibiting inward calcium current and subsequently the release of acetylcholine into the synaptic cleft.
History and exam
- serial PFTs
- total-body fluoro-2-deoxyglucose positron emission tomography (FDG-PET) scan
- high-frequency or tetanic repetitive nerve stimulation (RNS)
- single-fiber electromyography
- HLA haplotyping
- thyroid-stimulating hormone (TSH)
- antinuclear antibodies (ANA)
- rheumatoid factor (RF)
- antineutrophil cytoplasmic autoantibodies (ANCA)
- B12 and methylmalonic acid (MMA)
Joshua P. Alpers, MD
University of Tennessee Erlanger Neurology
JPA declares that he has no competing interests.
Vern C. Juel, MD
Associate Professor of Neurology
Department of Neurology
Duke University Medical Center
VCJ declares that he has no competing interests.
David Stickler, MD
Medical University of South Carolina
DS declares that he has no competing interests.
Zaeem Siddiqui, MD, PhD
Division of Neurology
University of Alberta
ZS declares that he has no competing interests.
Paul Wirtz, MD, PhD
Department of Neurology
PW is an author of a number of references cited in this monograph.
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