Which medications in the drug class Cholinergic Agonists are used in the treatment of 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

Cholinergic Agonists

Cholinergic agonists produce symptomatic improvement in strength, autonomic symptoms, or both in some patients with LEMS. They act by inhibiting the breakdown of ACh, which is intended to help compensate for the relative lack of ACh quanta release in LEMS. They usually do not provide a significant improvement; however, a few patients with mild disease may note some difference.

Acetylcholinesterase inhibitors do not usually produce dramatic improvement in LEMS, but they may provide relief from weakness or dry mouth in some patients. Pyridostigmine is the preferred agent and should be administered for several days before assessing response.

Pyridostigmine bromide (Mestinon, Regonol)

Pyridostigmine blocks ACh hydrolysis by cholinesterase, resulting in ACh accumulation at synapses and increasing stimulation of cholinergic receptors at myoneural junction.

In most of the literature, the consensus seems to be that monotherapy with a cholinesterase inhibitor is ineffective. It is in combination with drugs such as 3,4-diaminopyridine that cholinesterase inhibitors may have some slight benefit.

Guanidine

Guanidine is thought to act by increasing free intracellular calcium concentrations through inhibition of mitochondrial respiration by blocking potassium channels, and thus prolonging the nerve terminal action potential. This increases release of ACh after nerve impulses and may decrease rates of repolarization and depolarization of muscle cell membranes. It temporarily improves strength in many patients with LEMS. Maximal effect may take 2-3 days. It is indicated in adults to reduce symptoms of muscle weakness and easy fatigability associated with LEMS.


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