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Medical Policy

Policy Num:      02.007.001
Policy Name:    Repetitive Nerve Stimulation
Policy ID           [02.007.001]  [Ar / L / M-+ / P-]  [0.00.00]

Last Review:    June 22, 2023
Next Review:    Policy Archived
 

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Related Policies: None

Repetitive Nerve Stimulation
 

summary

Repetitive nerve stimulation (RNS) and single-fiber electromyography (SFEMG) are important confirmatory tests for the diagnosis of disorders of the nicotinic neuromuscular junction, particularly for myasthenia gravis, Lambert-Eaton myasthenic syndrome (LEMS), and botulism.

Repetitive nerve stimulation – Repetitive nerve stimulation (RNS) represents a modification of conventional motor nerve conduction studies. The interval between repeated motor nerve stimulations is designed to maximally stress the neuromuscular junction safety factor. (See 'Repetitive nerve stimulation' above.)

•Slow RNS – Slow rates of RNS (1 to 5 Hz) deplete the number of quanta of acetylcholine available for release with subsequent depolarizations. In pathologic states where the safety factor for neuromuscular junction transmission is considerably reduced, some muscle fibers will fail to depolarize in the later stimuli of a train and the compound muscle action potential (CMAP) amplitude will drop, which is referred to as a decremental response (waveform 1). A reproducible decrement of >10 percent is considered abnormal in most muscles.

•Rapid RNS – In disorders of the presynaptic terminal of the neuromuscular junction, where the number of released vesicles is markedly reduced, voluntary maximal isometric muscle contraction or high-frequency RNS can markedly increase the release of acetylcholine and thus enlarge the size of the resultant CMAP amplitude and area, which is referred to as an incremental response (waveform 2). 

Objective

The purpose of this review is to evaluate testing for disorders of the neuromuscular junction.

Policy Statement

Triple-S considers for payment  "Repetitive Nerve Stimulation (RNS)" when criteria for  medically necessity exists for the diagnosis and evaluation of disorders of the  neuromuscular junction.

Policy Guidelines

Diagnosis and evaluation of myasthenia gravis

	Generalized myasthenia percent positive	Ocular myasthenia percent positive
AChR antibodies	80 to 90	40 to 55
MuSK antibodies (in AChR antibody-negative patients)	40 to 50	<10
Repetitive nerve stimulation	75	<50
Single-fiber electromyography	92 to 99	80 to 95

AChR: acetylcholine receptor; MuSK: muscle-specific tyrosine kinase.

Benefit Application

BlueCard/National Account Issues

Benefits are determined by the group contract, member benefit booklet, and/or individual subscriber certificate in effect at the time services were rendered.  Benefit products or negotiated coverages may have all or some of the services discussed in this medical policy excluded from their coverage.

Background

The nicotinic neuromuscular junction is a complex, specialized structure incorporating the distal axon terminal and the muscle membrane that allows for the unidirectional chemical communication between peripheral nerve and muscle. It consists of the presynaptic nerve terminal, the synaptic cleft, and the postsynaptic endplate region on the muscle fiber. Acetylcholine serves as the neurotransmitter for voluntary striated muscle.

With a neuromuscular junction disorder of the postsynaptic membrane such as myasthenia gravis, the number of acetylcholine receptors is reduced, and this in turn reduces the safety factor for muscle fiber activation.

In disorders of the presynaptic terminal, such as Lambert-Eaton myasthenic syndrome (LEMS), the number of released vesicles is markedly reduced at baseline.

A complete electrodiagnostic study including nerve conduction studies (NCS) and electromyography (EMG) is a standard component of the evaluation of neuromuscular junction disorders. However, additional techniques may be required to assess the fidelity of neuromuscular junction.

Under most circumstances, these studies are normal in postsynaptic neuromuscular junction disorders, such as myasthenia gravis. Presynaptic neuromuscular junction disorders such as the Lambert-Eaton myasthenic syndrome (LEMS) often have a pattern of low compound muscle action potential (CMAP) amplitudes with normal motor latencies and normal sensory nerve action potentials. It is only with RNS or SFEMG that the true nature of the disorder is demonstrated.

REPETITIVE NERVE STIMULATIONRepetitive nerve stimulation (RNS) represents a modification of conventional motor nerve conduction studies.

The presence of this decremental response on RNS has been the neurophysiologic hallmark of myasthenia gravis. Suspicion of myasthenia gravis (MG) remains the major indication for the procedure.

Myasthenia gravis is not the only etiology associated with a decremental response, especially if the decrement increases through the nine or more stimuli in a train. The differential diagnosis is not usually clinically difficult, but conventional nerve conduction studies and electromyography are usually necessary. Conditions that have been noted to induce decremental responses include the following:

●Lambert-Eaton myasthenic syndrome (LEMS)

●Radiculopathy

●Motor neuron disease

●Peripheral neuropathy

●Polymyositis

●Some myopathies (McArdle disease, paramyotonia congenita, hyperkalemic periodic paralysis, etc)

●Medication effects (especially d-penicillamine, aminoglycosides, and nondepolarizing neuromuscular blocking agents)

●Botulism

●Organophosphate poisoning

Population Reference No. 1 

RNS studies can identify impairment of neuromuscular transmission when repeated stimulation of a motor nerve shows a progressive reduction in the amplitude of the compound muscle action potential (CMAP)

Suplemental Information

N/A

References

1. Howard JF Jr. Neuromuscular transmission. In: Neuromuscular function and disease: Basic, clinical and electrodiagnostic aspects, 1st edition, Brown WF, Bolton CF, Aminoff MJ. (Eds), W.B. Saunders Company, Philadelphia 2002. Vol 1, p.401.

2. Baker PF. Calcium and the control of neuro-secretion. Sci Prog 1977; 64:95.

3. Preston DC, Shapiro BE. Repetitive nerve stimulation. In: Electromyography and neuromuscular disorders: Clinical-electrophysiologic correlations, 2nd edition, Butterworth-Heinemann, 2005. p.66. Petretska A, Jarrar R, Rubin DI. Radial nerve repetitive stimulation in myasthenia gravis. Muscle Nerve 2006; 33:817.

4.https://www.uptodate.com/contents/diagnosis-of-myasthenia-gravis?search=Repetitive%20Nerve%20Stimulation%20(RNS)%20§ionRank=2&usage_type=default&anchor=H19&source=machineLearning&selectedTitle=3~28&display_rank=3#H19

5.uptodate.com/contents/electrodiagnostic-evaluation-of-the-neuromuscular-junction?search=Repetitive%20Nerve%20Stimulation%20(RNS)%20&source=search_result&selectedTitle=1~28&usage_type=default&display_rank=1

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