This document provides information about repetitive nerve stimulation (RNS) testing, including: 1) RNS is used to evaluate neuromuscular junction disorders like myasthenia gravis by assessing changes in the compound muscle action potential with repetitive nerve stimulation. 2) In myasthenia gravis, the safety factor is reduced due to fewer acetylcholine receptors, so some endplate potentials may not reach threshold, causing a decremental response on RNS. 3) The protocol for RNS involves stimulating multiple nerves at rest and after exercise to look for an abnormal decremental or incremental response that indicates impaired neuromuscular transmission.

1. REPETITVE NERVE
STIMULATION (RNS)
By: SyedIrshadMurtaza
NeurophysiologyDept AKUH
Karachi
Date:12-06-2013

2. Content
 Introduction to RNS
 Normal neuromuscular junction physiology.
 Myasthenia gravis.
 Lambert Eaton Myasthenic Syndrome (LEMS)
 Repetitive nerve stimulation (Types)
 Technical Factors that affect the RNS.
 Calculations of Decremental and incremental
responses.
 Protocol of RNS in EMG lab
 Protocol for evaluating NMJ disorder.

3. INTRODUCTION TO RNS
Also called Jolly test described first by Dr
Friedrichson Jolly in 1895.
RNS has been validated as one of most useful
electrophysiological tests in the evaluation of the:
 Patients with suspected Neuromuscular Junction
Disorder which includes:
 Myasthenia Gravis Syndrome.
 Lambert Eaton Myasthenic Syndrome.
 Botulism

4. Cont.
 CLINICAL PRESENTATION INCLUDES:
 Fatigability
 Proximal muscle weakness.
 Dysphagia
 Dysarthrai
 Ocular abnormality.
All of these are suggestive of possible NMJ
disorder.

5. ANATOMY ANDPHYSIOLOGY OF
NEUROMUSCULARJUNCTION
The NMJ essentially forms an
electrical-chemical- electrical link between the nerve and
muscle.
The chemical neurotransmitter at the NMJ is Acetylcholine
(ACH).
ACH molecules are packaged as vesicles in the presynaptic
terminal in discrete units known as Quanta (Bags of
neurotransmitter (ACH).)
The quanta are located in three separate stores:
Primary or immediately available store
1000 quanta- beneath presynaptic nerve terminal membrane.
Secondary or mobilization store
10,000 quanta- supplies the primary stores after few seconds.
Tertiary or reserve store.
More than 10,000 quanta –in the axon and cell body

6. PHYSIOLOGY
 When an nerve action potential invades and depolarizes the
presynaptic junction, voltage dependent calcium channels are
activated, allowing an influx of calcium.
 Results in release of ACH from the presynaptic terminals
 The greater the calcium inside the greater the more quanta (ACH) are
released.
 ACH then diffuses across the synaptic cleft and binds to ACH
receptors (ACHRs) on the post synaptic membrane
 In the post synaptic membrane – numerous junction are found with
ACH dependent gated channels and receptors.
 Thus the binding of ACH to ACHRs clustered opens ion channels…
resulting in a local depolarization, the End Plate Potential (EPP).
 The size of EPP depends on the amount of ACH that binds to the
ACHRs.

7. RNS EFFECT
During repetitive nerve stimulation in normal subjects,
ACH quanta are progressively depleted from the
primary store and fewer quanta are released with each
stimulation.
The corresponding EPP falls in amplitude but b/c of
normal safety factor it remains above the threshold to
ensure generation of a muscle action potential with
each stimulation.
After few seconds(1-2sec) the secondary store begins to
replace the depleted quanta with a subsequent rise in
the EPP.

8. PHYSIOLOGY OF RAPIDRNS
In rapid RNS (10-50 Hz), depletion of quanta from the presynaptic
terminals is counterbalanced not only by the mobilization or
secondary stores but also by accumulation of calcium.
Normally it takes 100 msec for ca2+ to diffuse back out of the
presynaptic terminals. If RNS is rapid enough so that new ca2+
influx occurs before previously infused ca2+ had diffused back
out, ca2+ continues to accumulate in the presynaptic terminals,
causing an increased release of quanta.
This combination of factors usually leads to an increased number of
quanta released and a corresponding higher EPP. However, the result
in normal subject is same ,i.e the generation of a muscle action
potential.

9. SLOWANDRAPIDRNS
 The effect of rapid and slow RNS is the same to generate the Muscle
action potential in normal subjects.
In Pathological Conditions:
 Where the safety factors is reduced, i.e the baseline EPP is reduced
but still above the threshold) the slow RNS will cause depletion of
quanta and may drop the EPP below threshold, resulting on the
absence of muscle action potential.
 In pathological conditions, where the baseline EPP is below the
threshold and a muscle action potential is not generated, rapid RNS
may increase the number of quanta released, resulting in a larger EPP
so that threshold is reached.
 This is the concept of increment with rapid RNS that are seen in
neuromuscular Junction Disorders.

11. Physiology of Myasthenia
Gravis
In patients with MG, the number of ACHRs is
reduced, lowering the safety factor. During
RNS, some EPPs may not reach threshold and
no action potential is generated. This results in
the decrement in the amplitude of the CMAP
and basis for the Decremental response in
Repetitive Nerve Stimulation in Myasthenia
Gravis Syndrome.

12. Repetitive Nerve Stimulation (RNS)

13. CALCULATIONS
Decremental response:
 The decrement is usually calculated by comparing
the lowest CMAP amplitude or area to the baseline
CMAP.
 (lowest CMAP divided by baseline CMAP).
 With 3 Hz stimulation the lowest CMAP is usually
the 4th
.

14. Normal MG
safety factor =15, n=quantas available, m= quantas released.
Stimulus n m EPP MFAP CMAP
1 1000 200 20 + Normal
2 800 160 16 + Normal
3 640 128 13 - Dec
4 512 102 10 - Dec
5 640 128 13 - dec
Stimulus n m EPP MFA
P
CMAP
1 1000 200 20 + Normal
2 800 160 16 + Normal
3 640 128 13 - Dec
4 512 102 10 - Dec
5 640 128 13 - dec

16. LAMBERT-EATON MYASTHENIC SYNDROME (LEMS)
 LEMS is a disorder of NMJ transmission characterized by
reduced release of ACH from the presynaptic terminal.
 There is now clear evidence that this disorder, like MG, is an
immune-mediated disorder. The pathogenesis of
LEMS is fairly well understood and involves the production of IgG
antibodies directed at the presynaptic voltage gated calcium
channel (VGCC). These antibodies interfere with the calcium-
dependent release of ACH
quanta from the presyn
aptic membrane and subsequently
cause a reduced endplate potential on the postsynaptic
membrane, resulting in NMJ transmission failure.

17. Clinical Presentation
LEMS is quite rare. It affects adults, generally those
older than 20 years and usually older than 40
years, of whom 70% are male and 30% are female.
Clinically, these patients present with proximal
muscle weakness (especially the lower extremities)
and fatigability.
 The distinctive clinical finding is that of muscle
facilitation.
After a brief period (10 seconds) of intense exercise
of a muscle, the power and the deep tendon reflex
to that muscle are transiently increased.

18. Incremental Response
 The increment is usually calculated by comparing the highest CMAP
amplitude orarea with the baseline CMAP
 (highest CMAPdivided by baseline CMAP).
 Why we take 4th
response
 In patients with MG, this decremental response usually has a
maximumdecrement at the fourth orfifth response and then a
tendency toward repair, by reaching of the next stimulus.

20. PROTCOL FORRNS IN EMG
LAB
I. Record one uppermotorNCS
II. Record one uppersensory NCS
III. Record RNS frommotornerves at 3 Hz. If trapezius
response is not satisfactory, record fromthe deltoid.
IV. EMG of proximal Muscle is performed, if RNS study is
negative.
RNS can be performed by using any of the motornerve. The
most commonly used are:
 Ulnar(ADQ)
 Accessory (Trapezius)
 Facial (Orbicularis Oculi)
 Axillary (Deltoid)
 Musculocutaneous (Biceps)

21. RNS PROTOCOL
 Slow Repetitive Nerve Stimulation (RNS) is performed in following sequence
 One Distal and one proximal motor nerves(preferable most involved muscles)
 One Sensory nerve
 RNS protocol
 Resting or base line trace 6 trains at-least (10 trains are preferred)
 Post 10 second exercise 6 trains
 Post 1 minute exercise 6 trains
 1 minute post 1 minute exercise 6 trains
 2 minute post 1 minute exercise 6 trains
 3 minute post 1 minute exercise 6 trains
 4 minute post 1 minute exercise (optional) 6 trains
 If decrement is noted, perform Post 10 second exercise stimulation 6 trains, for
facilitation
 In Myasthenia gravis persistent Decremental Response > 10% is abnormal. The
maximum Decremental response is noted 2 or 3 minute post 1 minute exercise.
 If patient is unable to perform exercise, fast RNS at 30Hz or 50Hz may be used.

22. Exercise
 Exercise play an important role in the
electromyography evaluation of patients with
suspected NMJ disorders.
 Brief maximal voluntary exercise can be used
instead of rapid RNS in cooperative patients.
 Exercise testing has distinct advantage of
being painless,where as rapid RNS is quite
painful and often difficult to tolerate.

23. POST EXERCISE EFFECT
 In normal subjects with a normal safety factor slow
RNS is performed immediately after exercise and then
1,2,3,4 minutes later, the EPP never falls below the
threshold and the CMAP and area will remain the
same.
 In patients with impaired NMJ transmission, however,
the decrement in CMAP amplitude and area in
response to slow RNS becomes more marked in 2-4
minutes after the exercise.

24. ABNORMALDECREMENTAL
RESPONSE
 Any decrement of more than 10% is defined as
abnormal. Normal subjects should have no
decrement. The 10% cut off allows for
inherent technical factor that are often
encountered. However any reproducible
decremental response of more than 10% is
considered abnormal.

25. TECHNICAL FACTORS THAT
AFFECT RNS:
 Lower temperature.
 Immobilization of Electrodes position.
 Supramaximal Stimulation.
 Administration of ACh inhibitors . (use of
medicine).
 Nerve Selection.
 Stimulation Frequency.
 Number of Stimulations.

26. Temperature
 Lower temperature increases the amplitude of the
CMAPs. Patients with MG may report clinically
significant improvement in cold temperatures. Thus
ice bag test can be very helpful in MG.
Typically they report worsening of ptosis in bright
sunlight or on a warm day. Therefore maintaining a
constant and perhaps higher-than-ambient
temperature during RNS testing is important to bring
out abnormalities of NMJ function. Temperature of
skin overlying the tested muscle should be at least
34°C.

27. INHIBITORSSHOULDBEWITHHELD
PRIORTOSTUDY
 It is best to advise patients to refrain from
taking acetylcolineasterase inhibitors
(e.g., Pyridostigmine Mestinon) for 6-8 hours
before the study, unless medically
contraindicated. These agents make more
ACH available to bind at the ACHRs and may
potentially diminished CMAP decrement,
resulting in a normal study.

28. IMMOBILIZATION OF
ELECTRODES
 If the electrode is immobilized ---- result is the change in the
CMAP amplitude which lead to misinterpretation.
 So the recording electrodes should be secured well with tape.
 Stimulator secured with Velcro Strap
 Entire Hand with pad or board.
The Goal is to minimize the movement of the limb.
SUPRAMAXIMAL STIMULATION:
Sub maximal stimulation can give art factual decrement or Increment
in the CMAP amplitude.
So always Check to ensure that the stimulus is supra maximal before
beginning of RNS

29. STIMULATION FREQUENCY
The optimal frequency for RNS is 2 or 3Hz
Reason:
RNS must be kept low to avoid accumulation of calcium at
presynaptic terminals.
NUMBEROF STIMULATIONS
 A train of 5-10 impulses is preferable for slow RNS. The
number should be kept minimum for the patients comfort.
As when the mobilization or secondary stores begins to re supply
the immediately available store , the decrement begins to
improve. The result is so called U Shaped Decrement. Which is
a characteristic of NMJdisorders.

30. ProtocolForEvaluatingDisorderOf NMJ
 Warm the extremity (33 degree centigrade)
 Immobilize the muscle as best as possible
 Perform Routine NCS first to ensure that the
nerve is normal
 Perform RNS at rest. After making sure that the
stimulus is supramaximal, perform at 3 Hz
RNS, normally there is a less than 10%
decrement b/w the first and the fourth
response.

31. Cont. Protocol
 If more than 10% decrement occurs and is consistently
reproducible:
 Has patient perform maximal voluntary exercise.
 Immediately repeat 3 Hz RNS post exercise
 If a less than 10% decrement or no decrement:
 Has patient perform maximal voluntary exercise for 1 min
and perform 3 Hz RNS immediately and at 1,2,3 and 4
mins.
 If a significant decrement occurs after 1 min exercise (post
exercise Exhaustion), have patient perform maximal
voluntary exercise again for 10 sec and immediately repeat
RNS at 3 Hz to demonstrate repair of the decrement.

32. Cont. Protocol
 Perform RNS on one distal and one proximal
muscles especially the weak muscles.
 If no decrement is found with a proximal limb
muscle, a facial muscle can be tested.
 If the compound muscle action potential is low at
baseline, have patient perform 10 sec exercise, then
stimulate the nerve supramaximally immediately
post exercise, looking for an abnormal increment
response ( greater than 140% of the baseline). If the
patient cannot exercises, rapid RNS should be
used.

33. Thank you for the patience..