1. The document discusses various electrophysiological tests including repetitive nerve stimulation test (RNST), visual evoked potentials (VEP), and brainstem auditory evoked responses (BAER). 2. RNST involves electrically stimulating a motor nerve repeatedly to observe changes in the compound muscle action potential. Abnormal results can indicate disorders of the neuromuscular junction like myasthenia gravis or Lambert-Eaton myasthenic syndrome. 3. VEP involves recording electrical potentials from the visual cortex in response to visual stimuli. Pattern reversal VEP using checkerboard patterns is commonly used to detect lesions of the visual pathway. P100 latency prolongation is the most reliable indicator of abnormality.

1. Dr Sankalp Mohan
Senior Resident
Neurology
GMC, Kota
Basics of RNST,VEP ,BAER

2. Repititive Nerve Stimulation
Test
 Variant of the Nerve conduction Study
 First Described by German Neurologist Jolly in
1895
 Harvey and Masland(1941) reported electrical
decremental muscle response on repetitive motor
nerve stimulation.
 electrical stimulation is delivered to a motor
nerve repeatedly several times per second-
observing the change in the CMAP

3. Definitions
 Quantum.- A quantum is the amount of Ach
packaged in a single vesicle (5000-10000
molecules )
 Miniature EPP –Presynaptic terminals
spontaneously release Ach quantum Causing
MEPP
 End plate potential -EPP is the potential
generated at the postsynaptic membrane
following a nerve action potential and
neuromuscular transmission

4.  Muscle action potential (MAP) – If EPP
exceeds threeshold generated MAP
 CMAP – Sum of MAPs generated by no of fibres
 Safety Factor –Amplitude of EPP above
threshold needed to generate MAP

6. Physiology of RNS
 Ach stores: immediately available (primary)
store and secondary (or mobilization) store
 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

7.  - Low Rate RNS – (<5 Hz) – Progressive decline of Ach
Quanta from Primary store
 EPP falls in amplitude but -normal safety factor it remains
above the threshold to Generate muscle action potential with
each stimulation.
.- After first few seconds secondary mobilization store
replaces depleted quanta
-- Rapid RNS
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+ Causing
increased release–
.

8. S
A- Normal
B- Postsynaptic slow RNs
C- Presynaptic Slow RNS
D. – Presynaptic – Rapid RNS

9. 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 or 5th

10. Variables affecting RNS
Age- Newborns CMAP is 30 – 50 % of adults
Temperature – cooling decreases and warming
increases the CMAP decrement. Temp
recommended 26-33 degree.
Muscles tested - Proximal or distal .ADM -7 %
Deltoid- 13 %
Exercise can result in Facilitation/Exhaustion

11. Technique
 Anticholinesterases withheld 24 hrs prior to study
 Recording Electrodes placed in Belly Tendon
Montage
 Immobilization of Electrodes and Limb
 Muscles –1. Deltoid Highest diagnostic yield (78%) ,
Trapezius (65%).
2. ADM Technically easier less diagnostic
3. Facial nerve – Nasalis /Orbicularis Oculi .
CMAP amplitudes are small . Immobilization
difficult .
- Stimulation Frequency for Low Rate RNS – 2to 3 Hz
- Number of Stimulations – Train of 5 to 10 Pulses

12. Exercise testing or Tetanic
Stimulation
 Maximum Voluntary contraction of Involved
muscle for 10 seconds, F/b 3 Hz RNS – Post
exercise Facilitation
 Maximum voluntary exercise for 1 min
Slow RNS at 1,2,3,4 Min – Post Exercise
Exhaustion
Psuedofacilitation – seen in normal individuals
Following exercise .CMAP amplitude increased but
area same . Does not exceed >40%

13. Protocol For Evaluating Disorder
Of 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.

14.  If more than 10% decrement occurs and is
consistently reproducible Patient Has patient
perform maximal voluntary exercise.
Immediately repeat 3 Hz RNS post exercise
 If 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.

15.  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

16. Rapid RNS
 optimal frequency is 20–50 Hz,for 2–10 seconds
 brief (10-second) period of maximal voluntary
isometric exercise has,the same effect as rapid
RNS
 Depletion of quanta vs calcium accumulation
 Incremental response in LEMS

17.  MG is considered to be a reproducible 10%
decrement in amplitude when comparing the
first stimulus to the forth or fifth, which is
found in at least 1 muscle.
 Abnormality in LEMS is considered to be a
reproducible postexercise increase in
amplitude of at least 100% as compared to
preexercise baseline value.

18. Myasthenia Gravis
 Classic Findings
 1. Normal CMAP
 2. Decremental Response at low rate RNS
 3. Normal or minimal post exercise facilitation
 4.Normal or decremental response at High rate
RNS
 5. Post Exercise or post tetanic Exhaustion

19. LEMS
 Classic Findings
 Low Normal CMAP
 Decremental Response at Low Rate RNS
 Post exercise facilitation
 High Rate RNS 100 % increment in two muscles
,400 % increment in one muscle

20. Utility of RNS
 Most commonly used test, easy.
 RNS is relatively insensitive,10-50% in ocular
myastenia,75% in generalised MG
 RNS is relatively specific(90%)
 SFEMG is Most sensitive.(90% in ocular,95%
in MG)

21. Visual Evoked Potentials

22. Evoked Potential
Electrical potentials that occur in the cortex after
stimulation of a sense organ which can be
recorded by surface electrodes is known as
Evoked Potential.
eg. SEP, BAER and VEP

23. VEP
 VEPs are electrophysiologic responses to
stimulation by either patterned or unpatterned
visual stimuli.
 Stimulation at a relatively low rate (up to 4/s) will
produce “transient” VEPs
 Stimulation at higher rates (10/s or higher) persist
for the duration of the stimulation and are referred
to as “steady-state” VEPs.
 Responses evoked by patterned stimuli are
“pattern” VEPs
 Responses evoked by unpatterned stimuli are
“flash” VEPs

24. Choice of Stimulus
 Patterned visual stimuli elicit responses that have
far less intra- and interindividual variability
 greater sensitivity and accuracy
 Checkerboard pattern reversal is the most widely
 Unpatterned stimuli are generally reserved for
patients who are unable to fixate or to attend to
the stimulus

25. Physiologic basis
 The generator site for VEPs is believed to be the
peristriate and striate occipital cortex

26. Pretest Evaluation
 Test should be explained
 Ability to fixate important throughout
 Avoid Hair Spray or Oil
 Cycloplegics generally should not be used
 Subjects with refractive errors should be tested
with appropriate corrective lenses

27. Electrode Placement
 Standard Disc EEG electrodes usede
 Active/Recording Electrode Placed at Oz in
midline 4cm above Inion
 Reference Electrode FPz 12 cm above Nasion.
 Ground Electrode placed at vertex Cz

29. Pattern Reversal Visual Evoked
Potential Testing
 Negative and positive polarities are designated N
and P, respectively.
 Peak latencies are expressed in milliseconds
 Peaks N75, P100, and N145 are recorded over
the occiput
 Wave Nl00 is recorded from the midfrontal region
 N145 is highly variable and is not used for
standard test interpretation
 Type of pattern.- Checkerboard ,Bar and
sinusoidal grating stimuli

30. Stimulus field types
 pattern that extends equally to both sides of the
fixation point is referred to as a full-field stimulus ‘
 A pattern presented to one side of the fixation
point in one-half – Half field stimulus
 pattern presented to a small sector of the visual
field is designated a partial-field stimulus
 half-field or partial-field stimuli are used, the
fixation point should be displaced to the
nonstimulated visual field by a small amount, to
prevent stimulation of both retinal hemifields

31. Test Protocol for Full-Field
Stimulation
 Full-field PVEP testing is most sensitive in detecting
lesions of the visual system anterior to the optic
chiasm
 should be performed monocularly,
 black-and-white checkerboard pattern,
 at a reversal rate of 4/s or less.
 The subject should be placed no closer than 70 cm to
the stimulus screen.
 Small checks (12—16‟) and small fields (2-4˚)
selectively stimulate central vision. These responses
are particularly sensitive to defocusing and decreased
visual acuity
 Recommended recording time window (ie, the sweep
length) is 250 msec; 50-200 responses are to be
averaged. A minimum of 2 trials should be given,

32. Electrode placement-
 Montages – International federation of Clinical
Neurophysiology (IFCN) recommends 2 channels
minimum
 Channel1 – Oz – Fpz
 Channel 2 – Oz – Linked ear
Four Channel montage
 Channel 1 : Oz –Fpz
 Channel 2- Pz- Fpz
 Channel 3 – L5-Fpz
 Channel 4 –R5 -Fpz

33. Factors Affecting VEP
 The size of the checks
 Pupillary size
 Gender (women have slightly shorter P100 latencies),
 Age: below 1 yr of age P100 may be 160ms, & above
60 yrs. also it get delayed- upto 120
 Sedation and anesthesia abolish the VEP.
 Visual acuity deterioration up to 20/200 does not alter
the response significantly .
 Drugs.

34. Waveforms
(The NPN complex)
 The initial negative peak (N1 or N75)
 ِA large positive peak (P1 or P100)
 Negative peak (N2 or N145)
N75
P100
N145

36. Clinically Significant Abnormality
 changes in latency, amplitude, topography, and
waveform
 P100 latency prolongation is the most reliable
indicator
 Waveform abnormalities are generally subjective
in nature and difficult to quantify
 Amplitude affected by technical Factors wide
individual variation – Hence interoccular
amplitude ratio used
 P100 is 110 milliseconds (ms) in patients younger
than 60 years .

37. Flash Visual Evoked Potential
Testing
 limited to: (1) subjects with severe refractive errors or
opacity of ocular media
 subjects who are too young or too uncooperative
 results should demonstrate reproducible peak positive
responses to flash stimulation
 consist of up to six major peaks in the first 250 ms
after flash
 Unpatterned visual stimuli commonly consist of brief
flashes of light with no discernible pattern or contour
 (LED) board can be viewed from a distance or LED
goggles can be placed directly over the eyes.
Goggles have the advantage of producing a very
large field of stimulation that minimizes the effect of
changes in direction of gaze

38. Clinical Applications of VEP
 VEPs are most useful for testing optic nerve
function and less useful for assessing
postchiasmatic disorders
 Non Specific for etiology
 Partial-field studies may be useful for
retrochiasmatic lesions; however, they are not
performed routinely
 VEP may be abnormal ( low amplitude ) in
Refractive error severe ,Retinal diseases

39.  Optic neuritis-MS – P100 latencies prolonged
with or without amplitude loss
 NMO – unrecordable P100 waveform with
reduced amplitude more likely
 Ischemic optic neuropathy – Attenuation of
amplitude earlier than latency
 Vit B12 deficency – Bilateral asymmetric
prolonged p100 latencies
 Papilledema only – VEP not affected

40. VEP in cortical blindness
 Some reports suggest that VEP may show a
varied result
OR normal VEP
 other reports suggest prognostic importance of
VEP with absent VEP response foretelling poor
prognosis
 INCONSISTENT PATTERN

41. Brainstem Auditory Evoked
Responses

42. BAER
 BAER are recorded from the ear and vertex in
response to brief auditory stimulation
 Actually a misnomer as responses from responses of
the auditory nerve, brainstem, and, perhaps, higher
subcortical structures

43. AEP
 Short latency AEP
 Middle latency AEP
 Long latency AEP
 The short latency AEP include peak of up to 10 msec
and amplitude of about 0.2uv, they are generated in
brainstem.
 The middle latency AEP have several variable peaks
with latency of 10-50 msec and with amplitude of
about 1 uv, they probably reflect early cortical
excitation.
 The long latency AEPs beginning after 50sec and
having peak of 1-10uv, represent later cortical
excitation

44. Auditory pathway

46. Electrode placement
 Typically are placed at the vertex (location Cz of
the International 10–20 System) and at both ear
lobes (Ai and Ac)
 Electrodes at the mastoids (Mi and Mc) may be
substituted, although wave I tends to be smaller
because of muscle noise

47. Montages Cz-Ai
Ac- Ai
May assist in the identification of wave

48. Stimulus
 “broad-band” clicks, the acoustic energy of
which is spread over a wide range of audio
frequencies
 100usec rectangular pulse (single
monophasic square wave)
 Stimulus Polarity -clicks in which the first and
major acoustic wave applies negative pressure in
front of the earspeaker diaphragm are referred to
as rarefaction clicks
 first and most prominent acoustic wave applies a
positive pressure in front of the earspeaker
diaphragm are referred to as condensation clicks

49.  Stimulus Rate –10 -70 times/s . Most common 11-
31 Hz
 Stimulus Intensity- about 70 db
 Click should be delivered monaurally, i.e., to one
ear at a time
 contralateral (nonstimulated) ear be masked by
white noise at 60 dB SPL to eliminate “crossover”
responses, i.e., bone-conducted responses

50. Waveform components
 Wave I - wave I response -in the distal portion of
cranial nerve (CN) VIII
 Prominent initial upgoing peak
 Wave II – Poorly defined in some adults and most
neonates. More prominent in contralateral channel
.Proximal VIII nerve /Cochlear nucleus

51.  Wave III: Prominent peak followed by trough .Arises
from Superior Olivary nucleus
 Wave IV: The ABR wave IV, which often shares the
same peak with wave V, arise from pontine third-
order neurons mostly located in the Lateral
lemniscus, but additional contributions may come
 Wave V: Most prominent peak appearing 5.5 ms
after stimulus. Wave v may fuse with wave IV .
Origin – Inferior colliculus
 Wave VI and VII: Thalamic (medial geniculate body)
and cortical region. Not clinically significant

53. Abnormalities of BAER
 Absence of waveforms
 Abnormal absolute or interpeak latencies
 Amplitude ratio abnormality
 Right to left asymmetry latencyof > 0.5 ms
- Wave II is difficult to distinguish ,Wave IV absence
may not be pathological

54. Abnormalities of Wave I
 Reflect peripheral auditory dysfunction, either
conductive or cochlear, or pathology involving the
most distal portion of the eighth nerve
 Poorly formed or absent wave I but a clear wave
V may reflect high-frequency hearing loss.
 May reflect intracranial pathology because the
cochlea receives its blood supply from the
intracranial circulation via the internal auditory
artery

55. Abnormalities of the I–III Interpeak
Interval
 Prolongation reflects an abnormality within the
neural auditory pathways between the distal
eighth nerve on the stimulated side and the lower
pons . Upper limit- 2.5 ms
 Seen in acoustic neuromas, demyelinating
disease, brainstem tumors, or vascular lesions of
the brainstem,meningitis ,Sub

56. Abnormalities of the III–V Interpeak
Interval
 Reflects an abnormality between the lower pons and
the midbrain most often, although not always,
ipsilateral to the lesion.Upper limit- 2.4 ms
 Prolongation not an abnormality if the I–V interpeak
interval is normal.
 Seen in a variety of disease processes involving the
brainstem, including demyelination, tumor, and
vascular disease

57. Abnormalities of the I-V Interpeak
latencies
 Upper limit – 4.5 ms
 Variety of disorders demyelination ,ischemia
 Wave V to I amplitude ratio –
 If ratio less than 50 % suggests central impairment
 Very high ratio suggests Peripheral impairment

58. Clinical Application
 Most Important is for Hearing assessment in
newborns and children
 Neurologic Conditions- Multiple Sclerosis ,
Stroke,Coma
 Retrocochlear Hearing loss – Acoustic Neuroma

59. Clinical Application
- Usually non specific and should be correlated
clinically and with other investigations
CP angle tumor –
 1. Unrecordable BAER
 2. Only wave I recordable
 3. Prolongation of I –III and I-V Interpeak
latencies
 4. Right to left asymmetry in wave V latency
- MRI is gold standard for evaluating retrocochlear
hearing loss
 BAER – 71 % sensitivity ,74 % specificity

60. Multiple Sclerosis –
1. Most frequent – Absence of Wave V
2. Prolongation of III-V interpeak latency
3. Prolongation of I-V interpeak latency
4. Reduction of V/I amplitude ratio
Diagnostic yield is higher in definite MS- 67%,Probable-
41% ,
Higher in those with brainstem signs
- Diagnostic yield Lower compared to VEP
- Can be used to detect silent brainstem lesions
,follow up and response to treatment

61. Coma and Brain Death
 Prognostic predictor of coma
 BAER is normal in toxic or metabolic cause of
coma
 Absence of III or IV waves associated with
vegetative state
 Better Predictor of outcome following head injury
than GCS
 In brainstem stroke abnormal BAEP correlated
with unstable clinical course

62. Role of BAER in pediatrics
 Newborn Hearing Screening – Hearing loss
occurs in 1/1000 births .Early detection to
improve language skills
 Hyperbilirubinemia/kernicterus
 Children with intellectual impairment
 Spastic Cerebral Palsy

63. THANK YOU

64. References
 Electromyography and Neuromuscular disorders –
David Preston ,Barbara Shapiro -3rd Edition
 Clinical Neurophysiology – UK Mishra & J Kalita – 3rd
Edition
 Practice parameter for repetitive nerve stimulation –
AANEM
 Guidelines on Visual Evoked Potentials 2008
American Clinical Neurophysiology Society (ACNS)
 ACNS guidelines for Auditory evoked potentials