NERVE CONDUCTION STUDY IS USEFUL FOR DIAGNOSIS OF NERVE LESION. Interpretation of NCV is dignostic tool for PNI.

1. Interpretation of NCV
Dr. Ketaki Patani
Associate Professor

2. Principle of NCV
1.In that recording electrodes the active electrode placed over
the muscle belly and reference electrode distal to the active
electrode.
2.In stimulating electrode , the cathode should be directed
towards the active electrode to avoid anodal block and the
stimulating electrode over the superficial part assessing nerve
.
3.The ground electrode over the neutral area between
stimulating and recording electrode
4.The stimulator, it stimulates the nerve with the square wave
pulses ,duration 0.1ms and intensity 100 and 300 v or 5 to
40mA and frequency 1 to 20 pulse/sec.
5.The patient should be comfortable and the muscles which is
being assessed are relaxed.

3. Principles of Motor conduction
velocity
 Motor or mixed nerve stimulated at least two points
along the course.
 Pulse is adjusted to record compound muscle
action potential.
 The surface electrode commonly used and placed
in belly tendon ; keeping the active electrode close
to the motor point and reference to the tendon.
 Ground electrode placed between stimulating and
recording electrode
 Biphasic potential with initial negativity recorded.

4. Principles of Motor conduction
velocity
 Motor or mixed nerve stimulated at least two points
along the course.
 Pulse is adjusted to record compound muscle
action potential.
 The surface electrode commonly used and placed
in belly tendon ; keeping the active electrode close
to the motor point and reference to the tendon.
 Ground electrode placed between stimulating and
recording electrode
 Biphasic potential with initial negativity recorded.

5. Principles of Motor conduction
velocity
 Motor or mixed nerve stimulated at least two points
along the course.
 Pulse is adjusted to record compound muscle
action potential.
 The surface electrode commonly used and placed
in belly tendon ; keeping the active electrode close
to the motor point and reference to the tendon.
 Ground electrode placed between stimulating and
recording electrode
 Biphasic potential with initial negativity recorded.

6. Motor nerve conduction velocity commonly
assessed muscle in various nerves
# In Upper limb:
Ulnar nerve – Abductor digiti minimi
Median nerve – Abductor pollicis brevis
# In Lower limb:
Peroneal nerve – Extensor Digitorum
brevis
Post tibial nerve – Abductor hallucis

7. Cont…
 Surface stimulation of healthy nerve
requires a square wave pulse of
0.1ms duration with an intensity of 5-
40mA.
 Filter setting: 5hz-10khz
 Sweep speed : 2-5ms/div
 Latency defined as time in ms.(from
the stimulus artifact to the first
negative deflection of CMAP.

8. Cont…
 The duration of CMAP is measured from the
onset of negative or positive peak or final
return of wave from baseline.
 Nerve conduction velocity expressed in
m/sec.
 Measurement of latency difference between
two point stimulation
Conduction velocity = distance / PL – DL m/sec
PL = proximal latency in ms
DL = distal latency in ms
D = distance between proximal and distal
stimulation in mm.

11. Principles
#As in general NCV study principles cathode (active ) (-)(black)
and anode (Inactive) (Red)(+)
# Orthodromic conduction of Motor nerve:
When the stimulus starts, the stimulus artifiact is seen at the left
of the screen, this is due to purely Mechanical, not a muscle
activity ; the supramaximal stimulation (more than 20% normal
action potential) is needed for compound Motor unit activity
production (i.e.) maximum depolarisation of all motor fibers.
When the muscle fibers begin to depolarize , the electrical potential
are transmitted through the volume conductor and the deflection
is seen in oscilloscope. This is called M wave. The M wave
represents the summated activity of all motor unit in the muscle
that responds to the stimulation of nerve.

12. CMAP
 CMAP latency due to – Measures fastest
conductivity of muscle fibers.
 CMAP Amplitude – Number of nerve fibers
 CMAP duration – density of small fibers

13. CMAP values
 Normal – shape – biphasic initial (-ve)
phase.
 NCV - normal In UL -40 to 70m/s
In LL – 50msm/s

14. NCV

15. Sensory conduction velocity
 NCV of sensory nerves can be measured in the
form of orthodromic conduction (in the physiologic
direction) or in antidromic conduction (opposite to
normal conduction) is used in distal portion of the
nerve. It is stimualted and SNAP recorded at a
proximal point along the nerve.
 Stimulus electrode is fixed over the base of the
middle digit innervated by the nerve using ring
electrode.

17. Cont…
 Orthodromic – distal portion of nerve is stimulated
and SNAP is recorded at proximal point along the
nerve.
 Antidromic – nerve is stimulated proximally and
SNAP recorded distally.
 SNCV measures large, heavily myelinated axons-
touch and vibration sensation.
 We don’t measure pain carrying fibers.

18. In display
 In display the stimulus artifact present first , the
latency measured from the evoked potential rather
than the initial deflection.
 Sensory tests require much greater amplifier
sensitive than do motor tests and this allows more
noise to interface with the recording.

19. SNCV

20. Cont..
 In SNAP potential; amplitude denotes the density
of nerve fibers and the duration denotes the
number of fibers involved.
 SNCV in U.L. = 45 to 75 ms
 Shape of SNEP = Sharp unlike rounded ‘M’ wave.
 Because of large diameter of sensory nerve it has
slight faster conduction velocity than in NCV.

21. TYPES

22. Variables that affect NCV
1.Age: Infant ½ of NCV than adult.
 Adult: Normal
 After 6 to 8 decade : NCV decrease (less than
10ms).
2. Limb variation: Due to short internodal distance
progressive reduction in Axonal diameter ,lower
temperature of feet compared to the hands in the
median and ulnar nerve conduction velocity is
higher compared to common peroneal nerve.

23. Cont..
 Temperature: Lower temperature decrease the
conduction velocity drops of 1.8 °F changes to 2 to
2.4 in conduction velocity maintain 21-23°c is optimal
for assessing the NCV.

24. LATE RESPONSES
 Late responses are the potentials appearing after
motor Response.(M Wave) It follows mixed nerve
potentials.
 Three important Responses:
1. H Reflex
2. F Response
3. Axon Reflex

25. ‘H’ Reflex
 The ‘H’ Reflex was described by Hoffman in 1918,
hence its name ‘H’ Reflex. The ‘H’ Reflex is a
monosynaptic reflex elicited by submaximal.
Stimulation of Tibial nerve and it is recorded from
the calf muscle. It is also assessed in other
muscles except the small muscles of hand and
feet.
 Pathway: Muscle spindle sensory nerves (IA)to
spinal cord.
Anterior horn cell to soleus muscle.
Elicited on submaximal stimulus and inhibited on
supramaximal stimulus.

26. Cont…
 The Reflex arc of ‘H’ Reflex include
a. Large fast conducting group of Ia fibers.
b. Spinal cord where different fibers synapse with
alpha motor neurons.
c. Efferent motor fibers supplying the muscles.

27. Stimulus
 Square wave pulse of 1ms duration.
 Frequency 1 in 5 sec
 At least 5 Hz response.
H Reflex latency = 0.46+ 9.14+0.1
(leg length) (Age in yr)
Normal value of latency of H Reflex
Soleus = 35ms
Flexor carpi radialis = 20ms.

28. H REFLEX

29. Clinical application
#The H Reflex latency is useful measure the
integrity of both sensory and motor fibers.
#A slowed latency is indicative of abnormal
dorsal root ganglion often from a herniated disc
or in impingement syndrome.
Because of this central involvement the
peripheral motor and sensory NCV would not
be affected.
# It is useful in the condition of
plexopathies,Radiculopathies,C6-C7
Radiculopathy and in GBS.

30. H - REFLEX

31. F Wave Response
 F wave is a reflex but due to antidromic activation
of alpha motor neuron.
 It is useful for diagnosis of proximal nerve lesion.
 Supramaximal stimulus needed for F wave
response and distal muscles are stimulated with
the rate of 0.5 Hz.(Faster stimulation). Amplifier
gain of 200-500 division ,5-10ms recommended.
 F response derives from the foot because it was
first recorded from the intrinsic muscles of foot.
 F response occurs in the latency 45 to 60 ms.

33. Cont….
 The stimulus leads to both orthodromic impulses
travels to distal muscle, the antidromic response
travel to AHC ; so depolarization both side produce
F response.
 F wave is useful measure the diagnosis the
condition of proximal portion of the axon involved
including GBS, thoracic outlet syndrome,Brachial
plexus injury ,Radiculopathies.
 In these condition the F wave response are slowed
or absent.
 F response absent in sleeping or sedated
condition.

34. F response
 In F response shows slowing
conduction velocity interpreted in
polyneuropathy.
 F response is shorter in arms than leg
because nerve of length travelled less.
 The prolong F response indicating
proximal nerve lesion.

37. Axon reflex
 Axon reflex is late potential generally appearing
between M and F wave. Axon reflex occur due to
collateral branching in the proximal portion of
nerves.
 On submaximal stimulation if only one branch is
stimulated , the impulse travels antidromically and
turns around descend down the unstimulated
branch to produce potential which is known as
Axon Reflex.

38. Cont…
 The conduction velocity of Axon reflex is slower
than normal ; axon reflex is abolished on
supramaximal stimulation.
 Axon reflex mostly present when the nerve
stimulated at wrist and ankle. Axon reflex has
constant latency and wave form.
 Axon reflex is found in various neurological
disorder such as Neuropathy,ALS,Carpal tunnel
syndrome,Tarsal tunnel syndrome,Brachial plexus
injury.

40. Blink reflex
 Afferent of blink reflex is mediated by
sensory fibers of the supraorbital
branch of opthalmic division of
trigeminal nerve and efferent by motor
fibers of facial nerve.
 Stimulation of trigeminal nerve to the
sensory nucleus of mid pons and
nucleus of spinal tract of the
brainstem.

41. BLINK REFLEX

42. Blink reflex procedure
 The patient should be in relaxed state with eyes either open
or gently closed.
 Active electrode is placed just lateral and inferior to the pupil
of midposition, with reference electrode placed just lateral to
the canthus.
 Ground electrode placed over the midforehead or chin.
 Sweep speed 5 or 10 ms/div.
 Sensitivity set 100 or 200μv /division.
 Motor filter setting 10 Hz or 10 khz.
 Stimulate each supraorbital nerve over the medial eyebrow
,recording orbicularis oculi bilaterally. Allow several second
between successive stimulation to prevent habituation.
 For each side, 4-6 stimuli tracing and determined shortest
response in latencies.

44. Blink reflex abnormalities
 It is seen in
1. Unilateral trigeminal lesion
2. Unilateral facial lesion
3. Unilateral midpontine lesion
4. Unilateral medullary lesion
5. Demyelinating peripheral neuropathy.

45. Repetitive nerve stimulation
study
 The neuromuscular junction is made up of a motor
neurone and motor end plate with synaptic cleft or
junctional gap dividing them.
 Low rate RNS – used for postsynaptic
neuromuscular transmission disorders. E.g.
Myaesthenia Gravis.
 High rate RNS – useful for diagnosis of presynaptic
neuromuscular transmission.g. Lambert eaten
syndrome.

46. REPITITIVE NERVE
STIMULATION

47. Important basic pattern
 Depending on underlying pathology
there are several pattern shows
conduction abnormalities.
 Disorders to find out abnormalities of
NMJ, anterior horn cell ,nerve or nerve
root.

48. Neuropathic lesion
 It mostly affect axon or myelin sheath.
 Demyelination associated with
dysruption of myelin
sheath,associated with entrapment or
commpressive neuropathies.

49. Axonal loss
 It most common pattern seen on
NCSs.
 Reduced amplitude is primarily
abnormality associated with axonal
loss.
 As axons are lost the amplitude of
potential is decreased.
 Axonal loss lesion generally with
reduced amplitude but it is not
corollary necessarily true, reduced

51. Abnormal patterns
 The normal distal latency (DL) ˂ 4.4 ms,
amplitude ˃ 4 mv and conduction velocity
˃49 ms.
 In axonal loss amplitude decrease and CV
slightly normal or prolonged.
 Demyelination associtated with prolonged
distal latency in that CV is normal.
 Demyelination with block /temporal
dispersion marked slowing of conduction
velocity and distal latency. This pattern
mostly seen in GBS or in acquired condition.

52. DEMYELINATION

53. Demyelination
 Myelin sheath is essential for saltatory
conduction.
 Without myelin sheth nerve conduction is
slowed or blocked.
 Demyelination associated with slowing of
conduction velocity.
 Motor,sensory and mixed nerve
conduction slower than 35m/s in upper
extremity and slower than 30m/s in lower
extremity velocity signifies unequivocal
demyelination.

54. Conduction block
 Conduction block present in
demyelinating lesion , CMAP depends on
site of stimulation and the location of
conduction block.
 If conduction block present in
demyelinating lesion CMAP amplitude
depends on the site of stimulation and
location of conduction block.
 A drop in amplitude because marked
abnormal dispersion from demyelinating
lesion.

56. Myopathy
 In myopathic disorder , results sensory
conduction normal CMAP amplitude is
low but distal latency and nerve
conduction velocities are normal.

57. Neuromuscular junction disorder
 Abnormalities of CMAP may be seen
depending on the pathology of
presynaptic or postsynaptic.
 In presynaptic disorder like lambert-
eaten mysthenic syndrome amplitudes
are low but amplitude and conduction
velocities within the normal limit.
 In postsynaptic disorders like
myasthenia gravis results CMAP is
normal.

58. NORMAL VALUES

59. NORMAL VALUES

60. SENSORY NERVE

61. SENSORY FOR UE

62. REFERENCES
 Electromyography and clinical neuromuscular
disorder: Clinical electrophyiological correlation 2ND
EDITION: David Preston & Barbara Shepario
 Kalitha Mishra
 Susan B.O’sullivan Physical Rehabilitation 7th
Edition
 Electrodiagnosis in nerve and muscle : Principle
and practice Edition 3- Jun Kimura