Lambert-Eaton myasthenic syndrome (LEMS)
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Etiology
- 50-70% of patients (especially men) have associated malignancy
- small cell lung carcinoma (most common)
- breast cancer
- prostate cancer
- gastric cancer
- autoimmune
- autoantibody against voltage-gated calcium channel
- association of LEMS with other autoimmune diseases
Epidemiology
- 3% of patients with small cell lung cancer[2][6]
Pathology
- autoantibody against voltage-gated Ca+2 channel alpha 1D (CACNA1D)
- impaired influx of Ca+2 into presynaptic terminals
- defective release of acetylcholine from presynaptic terminals
Clinical manifestations
- progressive proximal muscle weakness (especially legs)
- improves with repeated effort, then declines with sustained activity
- autonomic dysfunction
- diplopia
- ptosis (uncommon)
- impotency
- urinary dysfunction
- paresthesias
- dry mouth
- orthostatic hypotension
- muscle stretch reflexes
- generally spares muscles supplied by cranial nerves (in contrast to myasthenia gravis)
Laboratory
- serology:
- antibodies against SOX1 in 64% of the patients with LEMS secondary to small-cell carcinoma of the lung, but in 0% of patients with idiopathic LEMS[5]
- antibody to voltage-gated calcium channel CACNA1D[2]
Diagnostic procedures
- repetitive nerve stimulation study
- shows low amplitude motor unit potential with distal nerve stimulation that increases in amplitude with repeated stimulation (> 100% increase)[2]
- contrast with myasthenia gravis that shows a decrement in motor unit potential with repeated stimulation
Management
- glucocorticoids
- immunosuppressive agents
- plasma exchange
- intravenous immunoglobulin
- 3,4-diaminopyridine
- may increase acetylcholine release at the neuromuscular junction
- treatment of underlying malignancy
More general terms
Additional terms
References
- ↑ Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 640
- ↑ 2.0 2.1 2.2 2.3 Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15, 16, 17, 18. American College of Physicians, Philadelphia 1998, 2006, 2009, 2012, 2015, 2018.
- ↑ Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 624
- ↑ Geriatrics Review Syllabus, American Geriatrics Society, 5th edition, 2002-2004
- ↑ 5.0 5.1 Sabater L et al. SOX1 antibodies are markers of paraneoplastic Lambert-Eaton myasthenic syndrome. Neurology 2008 Mar 18; 70:924 PMID: https://www.ncbi.nlm.nih.gov/pubmed/18032743
Lang B and Evoli A. SOX1 autoantibodies: Tumor markers in LEMS patients? Neurology 2008 Mar 18; 70:906 PMID: https://www.ncbi.nlm.nih.gov/pubmed/18347313 - ↑ 6.0 6.1 Payne M, Bradbury P, Lang B et al Prospective study into the incidence of Lambert Eaton myasthenic syndrome in small cell lung cancer. J Thorac Oncol. 2010 Jan;5(1):34-8. PMID: https://www.ncbi.nlm.nih.gov/pubmed/19934775
- ↑ Petty R Lambert Eaton myasthenic syndrome. Pract Neurol. 2007 Aug;7(4):265-7. PMID: https://www.ncbi.nlm.nih.gov/pubmed/17636143
- ↑ Sanders DB, Guptill JT. Myasthenia gravis and Lambert-Eaton myasthenic syndrome. Continuum (Minneap Minn). 2014 Oct;20 (5 Peripheral Nervous System Disorders):1413-25. Review. PMID: https://www.ncbi.nlm.nih.gov/pubmed/2529929