Nerve Conduction Studies NCS
Nerve Conduction Studies NCS
Nerve conduction studies are an essential part of an EMG examination.
The clinical usefulness of NCS in the diagnosis of diffuse and local neuropathies has been thoroughly validated since the 1940’s
The findings reflect the functional state of the myelinated motor nerves, the neuromuscular transmission andthe muscle fibers.
Two motor units
StimulationStimulation
A nerve could be depolarized by:
Electrical Chock
Mechanical Compression
Magnetic Field
A nerve is a Chain of Polarized Cells (Myelin Action).
Stimulation in one point generates a depolarization.
+ -+ -+ -+ -+ -+ -+ -+ -+ -+ --+
Stimulation Points Upper
Extremities
Stimulation Points Upper
Extremities
Ulnar
Above Elbow
Ulnar
Below Elbow
Median
Elbow
Radial
Ulnar
Wrist
Median
Wrist
Median - Ulnar
Palmer
Plexus
Axillary
Stimulation Points Lower
Extremities
Stimulation Points Lower
Extremities
Crural
Peroneal Peroneal
Sciatic
Tibial
Popliteal fossa
Posterior
Tibial
Sural
Stimulation Points Head &
Trunk
Stimulation Points Head &
Trunk
Erb Point
Thora-
codorsalis
Long
Thoracic
Crural
Erb Point
Phrenic
Spinal XI
Auricular
Posterior
Trunk
Medium
Lower
Higher
Current Stimulation
Current StimulationCurrent Stimulation
NERVE + -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -
+ -
Supramaximal StimuliSupramaximal StimuliMin. 3 Times Sensory ThresholdMin. 3 Times Sensory Threshold
DepolarizationDepolarization
+ -
NERVE + -+ -+ -+ -+ -+ -+ -+ -+ -+ --+
Once a nerve is depolarized at some point,a wave of depolarization passes inboth directions from that point.
ANTIDROMIC ORTHODROMICANTIDROMIC ORTHODROMICANTIDROMIC ORTHODROMIC
Propagation - Refractory
Period
Propagation - Refractory
Period
+ -+ -+ -+ -+ --+ -+ + -+ -+ -+ -
+ -
NERVE
Propagation by Successive Depolarizationfollowed by Repolarization.
Time before Repolarization is called the Refractory Period.
Motor LatencyMotor Latency
Motor Response
MOTOR LATENCYin ms =
Propagation Timefrom S to M
-+ -+ + -+ -+ -+ -+ -+ -+ -+ -+ -
+ -
NERVE
S M
Motor ResponseMotor Response
Stimulation
Artifact
Onset
Latency
Amplitudes
Negative
Deflection
Peak to Peak
Peak
Latency
Duration
Area
Motor Conduction Median NerveMotor Conduction Median Nerve
Wrist
Elbow
Latency
Stim. 1
Stim. 2
Rec.
Recording: Surface Electrodes
Stimulation: Handgrip or Bipolar
3.5 ms
8.2 ms
Distance mm:
Diff.: 4.7 ms
C.V.: 51 m/s 240
Stimulation & Recording RULE
Stimulation & Recording RULE
BLACK TO BLACK
Stimulation Polarity: NEGATIVE
To reduce Stimulation Artifact as much as possible, Ground must be placed between Stim. & Rec.
To reduce Stimulation Artifact as much as possible, Ground must be placed between Stim. & Rec.
Nerve
Anode Cathode Active Reference
STIMULATION RECORDING
GROUND
Motor & Sensory General
Remarks
Motor & Sensory General
Remarks
MOTOR
• Amplitude 0.5 mV to 5 mV - Direct response
• Normally biphasic
• Duration 1 to 3 ms - Latency depends of stimulation site
• Stimulation Current depends on nerve and site, 15 - 30 mA
SENSORY
• Amplitude 5 µV to 35 µV
• Direct response for high amplitude potentials - otherwise
Averager is needed
• Normally biphasic
• Duration 1 to 3 ms - Latency depends on stimulation site
• Stimulation Current depends on nerve and site, 5 - 15 mA
Pathologic ResponsesPathologic ResponsesAmplitude Duration Latency
Normal Nl Nl Nl
Axonal Nl+/-
Degeneration
Conduction Nl+/-
Block
Severe Demyelination
Focal Nl Nl
Slowing
Myelin Damaged Nl = Normal
Carpal Tunnel CV General
Application
Carpal Tunnel CV General
Application
Stim. 1
Stim. 2
MOTOR Rec. Motor Median Nerve
Wirst
Elbow
Sensory Median and Ulnar Nerves
Digit 2
Digit 3
Digit 4
Latency
Stim.Digit 2.3.4
SENSORY
Rec.
Ulnaris Medianus
3.5 ms
6.2 ms
2.2 ms
2.4 ms
1.9 ms
Volontarycontralateralmotor actionto facilitate F
Stim.
Rec.
M
F
Minimum F Latency is normally measured
F-Waves Ulnaris NerveF-Waves Ulnaris Nerve
block
F Latence 30 to 50 ms
M F As playing with this game
F-WavesF-Waves
BlockBlockM
F
Shorter DistanceBetter Shoot!
Motor Neuron
10ms
Stim. Interval : ms
Refractory Period CV General
Application
Refractory Period CV General
Application
Stim.
Rec.
Double StimulationStart with 4ms delayDecrease by steps of 0.05ms
4.003.002.001.801.60
4.00
3.00
2.00
1.80
1.60
Refractory period: 1.80 ms
Digit V
Digit IV
Sensory Conduction Ulnaris
Nerve
Sensory Conduction Ulnaris
NerveStimulation
Recording
Latency ms 2.6
Latency ms 3.1
Distance mm 155
CV m/s 60
Distance mm 175
CV m/s 56
AVERAGINGAVERAGING
Rec.
1 inch dist.
between
Stim. Sites
Stim.
Palm
Wrist
No Stim.
Latency
Inching Ulnaris NerveInching Ulnaris Nerve
Increased Latency
Other graphics with Amplitude and Duration
Settings Settings MNCS SNCS
Rec. Sites All All Electrodes Surface Surface/Needle
High FQ (KHz) 2-5 2-5Low FQ (Hz) 20 20
Sensitivity mV/Div µV/DivInput 5 10AVG 5-10
Sweep Speed Upper 2 2ms/Div Lower 5 2
Stim. Intensity Supramaxima 3x Threshold
Duration ms 0.2 0.2Frequency c/s 1 1-3
Maximal recording amplitudeLower % diff. between2 sites
Normal Values Motor NCS Sensory
NCS
Normal Values Motor NCS Sensory
NCS
Age 20-50
Amp. Lat. C.V.
Nerve µV mV ms m/s
Median >20 <3.4 >50
Ulnar >15 <3.1 >50
Radial >18 <2.7
Median > 6 <4.0 >50
Median (palm) <2.2
Ulnar (palm) <2.2
Sural > 6 <4.5 >40
Peroneal <4.5
Peroneal > 3 <5.5 >40
Tibial (post.) > 8 <6.0 >40
The most sensitive normal value for
a particular NCS is usually obtained
by performing the same NCS on the
corresponding nerve in the contra-
lateral limb (assuming it is normal).
A decrease of more than 50% in
amplitude is considered abnormal.
The results of NCS - Motor, Sensory
must be compared to some normal
values.
These must be age-related as well.
Infants & young children:
Quite slow conduction rate.
Adults:Amplitudes and conduction ratedecrease with age.
Pitfalls Pitfalls
� High recording impedance electrode reducing amplitude
� Recording polarity inversion - incorrect onset latency
� Stimulation polarity inversion - increasing latency
� Unbalanced stimulation electrode - artifact
� Low stimulation intensity - impedance - infra stimulation
� Painful stimulation - movement artifact
� External interference (patient is an antenna)
� Incorrect setup - filters, sweep-speed...
