Repetitive nerve stimulation

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Repetitive nerve stimulation is a variant of the nerve conduction study where electrical stimulation is delivered to a motor nerve repeatedly several times per second. By observing the change in the muscle electrical response (CMAP) after several stimulations, a physician can assess for the presence of a neuromuscular junction disease, and differentiate between presynaptic and postsynaptic conditions. The test was first described by German neurologist Friedrich Jolly in 1895,[1] and is also known as Jolly's test.[2]

Medical uses[edit]

Repetitive nerve stimulation is used to diagnose neuromuscular junction (NMJ) disorders, the most common of which is myasthenia gravis. A decremental response (a smaller and smaller muscle response with each repetitive stimulus) is abnormal and indicates NMJ dysfunction. This can be further confirmed if the response normalizes after administration of edrophonium or neostigmine.[1]

Mechanism[edit]

Stimulation of a motor neuron causes it to release acetylcholine, which is stored up in vesicles at the axon terminal. The acetylcholine binds to nicotinic receptors on the muscle fiber, which open sodium channels and depolarizes the muscle cell.

As nerve stimulation is rapidly repeated, the acetylcholine stored in the nerve terminal is gradually depleted, and there is a slight weakening of the acetylcholine signal sent to the muscle fiber, resulting in smaller endplate potentials (EPPs). In normal muscle, although the EPPs become smaller with repetitive stimulation, they remain above the threshold needed to trigger muscle contraction. In myasthenia gravis, where many of the acetylcholine receptors are blocked, the EPP may exceed the threshold initially, but quickly falls below threshold with repetitive stimulation, resulting in the muscle fiber failing to contract. As one by one the muscle fibers fail to contract, the overall CMAP measured grows smaller and smaller, leading to the pathologic decremental response.

Preparation[edit]

As with all nerve conduction studies, the body part tested should be clean, free of lotions and conductive substances, with jewelry removed.

Procedure[edit]

Interpretation of results[edit]

Adverse effects[edit]

History[edit]

See also[edit]

References[edit]

  1. ^ a b Ropper, Allan H.; Samuels, Martin A. (2009). Adams and Victor's Principles of Neurology (9th edition ed.). McGraw Hill. pp. 1241–2,1410. ISBN 978-0-07-149992-7. 
  2. ^ Shin J. Oh. Clinical electromyography: Nerve Conduction Studies, page 20. Lippincott Williams & Wilkins, 2002. ISBN 978-0-7817-3681-7. Google books

External links[edit]

Jolly's myasthenic reaction at Who Named It?