November 22, 2010
Lambert-Eaton Myasthenic syndrome (LEMS) is characterized by three A's- Autonomic dysfunction, Areflexia and Ataxia. At autonomic synapses, it is believed that LES immunoglobulin impairs transmitter release at sympathetic and parasympathetic neurons through down-regulation of one or more subtypes of Voltage-Gated Calcium Channels (VGCC). This down-regulation inhibits autonomic transmission and likely underlies the symptoms of autonomic dysfunction observed in LES. The motor endplates of gamma motor neurons supplying the intrafusal muscle fibers of the muscle spindle have pre-synaptic VGCCs like those of alpha motor neurons. A pre-synaptic block affecting these intrafusal fibers would impair the function of these fibers, producing dysfunction in the afferent limb of the muscle stretch reflex resulting in areflexia. LEMS may co-exist with paraneoplastic cerebellar degeneration to produce ataxia. Studies have shown that LEMS patients have antibodies directed against VGCC in the molecular and Purkinje cell layers of cerebellum in the nonparaneoplastic LEMS.
1. Mareska M, Gutmann L. Lambert Eaton myasthenic syndrome. Seminars in Neurology. 2004 Jun;24(2):149-53.
Submitted by Suresh Subramaniam, M.D., M.Sc.
Disclosure: Dr. Subramaniam has nothing to disclose.
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