Clinical Clinical Electrophysiological Electrophysiological

AssessmentAssessment ((ENMG, EMG, NCV)ENMG, EMG, NCV)

Stephen Hearn, DPT, ECSStephen Hearn, DPT, ECSPresident – ENMG AssociatesPresident – ENMG Associates

Assessment of the Assessment of the integrity of motor and integrity of motor and sensory nerves, skeletal sensory nerves, skeletal muscles, selected muscles, selected reflexes and CNS reflexes and CNS pathwayspathways

Nerve Conduction Studies tell Nerve Conduction Studies tell us:us:

1.1. Are peripheral nerves involvedAre peripheral nerves involved2.2. Are sensory or motor fibers involvedAre sensory or motor fibers involved3.3. Location of the lesionLocation of the lesion4.4. Type lesionType lesion5.5. What processes (if any) of recovery What processes (if any) of recovery

or further degeneration are or further degeneration are occurringoccurring

6.6. Is the lesion isolated or evidence of Is the lesion isolated or evidence of an underlying disease processan underlying disease process

Equipment & Equipment & ParametersParameters

OscilloscopeOscilloscope viewing screen (negative is up)viewing screen (negative is up)

SweepSweep (horizontal measure) (horizontal measure) 1-500 ms/divisions- to measure speed.1-500 ms/divisions- to measure speed. 1-3 milliseconds per division for sensories1-3 milliseconds per division for sensories 3-5 milliseconds per division for motor 3-5 milliseconds per division for motor

studiesstudies Gain (sensitivity)/( vertical measure)Gain (sensitivity)/( vertical measure)

In microvolts to measure amplitude. Is In microvolts to measure amplitude. Is generally set at 5-20 microvolts per division generally set at 5-20 microvolts per division for sensory studies and 1000-5000 for sensory studies and 1000-5000 microvolts per division for motor studies.microvolts per division for motor studies.

Recording Electrodes- 3 Recording Electrodes- 3 typestypes

1.1. GroundGround - serves as zero voltage - serves as zero voltage reference point, for amplifier to reference point, for amplifier to reduce noise. Generally placed reduce noise. Generally placed over bone, tendon, or other over bone, tendon, or other non-conductive tissue between non-conductive tissue between the stimulator and recording the stimulator and recording electrodes or in close electrodes or in close proximity.proximity.

2.2. Recording Recording - - picks up evoked picks up evoked potential; usually black potential; usually black (negative). Placed over the (negative). Placed over the muscle belly for motor studies muscle belly for motor studies and directly over the nerve in and directly over the nerve in sensory studies.sensory studies.

3.3. Reference Reference - - picks up evoked potential; picks up evoked potential; usually red (positive). Generally placed usually red (positive). Generally placed distal to the recording electrodes in distal to the recording electrodes in motor studies, over less conductive motor studies, over less conductive tissue.tissue.3 cm distal to the recording electrode as 3 cm distal to the recording electrode as a rule but more important that a rule but more important that placement be over non-conductive placement be over non-conductive tissue, so distance may increase – which tissue, so distance may increase – which could reduce amplitude of the response. could reduce amplitude of the response. Placement Placement should not beshould not be < 3 cm or the < 3 cm or the signals may cancel one another. signals may cancel one another.

In performance of sensory studies, the In performance of sensory studies, the optimal placement is 4 cm distal to the optimal placement is 4 cm distal to the recording electrode and directly over recording electrode and directly over the nerve. the nerve.

Surface electrodesSurface electrodes

Pair of metal discs Pair of metal discs Bar electrodesBar electrodes Ring electrodesRing electrodes Clip electrodesClip electrodes

EMG needle electrodesEMG needle electrodes

Common length 25mm, 37mm, 50mm, Common length 25mm, 37mm, 50mm, 75mm75mm

Monopolar- need surface ground and Monopolar- need surface ground and reference; shaft is teflon coatedreference; shaft is teflon coated

Concentric Coaxial- wire is surrounded Concentric Coaxial- wire is surrounded by cannula, wire is active, shaft is by cannula, wire is active, shaft is reference, need surface groundreference, need surface ground

Bipolar- 2 wires in cannula (shaft). Bipolar- 2 wires in cannula (shaft). Active and reference, shaft is ground Active and reference, shaft is ground

Amplifiers: Amplifiers: converts low voltage potential converts low voltage potential to a higher voltage copy; uses common to a higher voltage copy; uses common mode rejection to get rid of noise.mode rejection to get rid of noise.

Filters: set frequency ranges to record Filters: set frequency ranges to record from from Notch: Notch: Eliminates frequency (60Hz)Eliminates frequency (60Hz) High cut High cut (low pass): Eliminates any signal at (low pass): Eliminates any signal at

a frequency greater than the settinga frequency greater than the setting Low cut Low cut (high pass): Eliminates any signal at a (high pass): Eliminates any signal at a

frequency lower than the settingfrequency lower than the setting

Equipment & Equipment & ParametersParameters

Equipment & Equipment & ParametersParameters Signal averagingSignal averaging

Utilized to amplify the response of very Utilized to amplify the response of very small potentials relative to physiological small potentials relative to physiological noise. With repeated stimulation, noise. With repeated stimulation, physiological and other noise will vary physiological and other noise will vary but the time locked nerve response but the time locked nerve response should remain consistent. The should remain consistent. The computer then amplifies the consistent computer then amplifies the consistent response while noise remains small response while noise remains small amplitude.amplitude.

Equipment & Equipment & ParametersParameters

Stimulator: monophasic square waveStimulator: monophasic square wave (-) cathode depolarizes(-) cathode depolarizes Intensity-to 400 volts or 90 milliampsIntensity-to 400 volts or 90 milliamps Duration-50-1000 microsecondsDuration-50-1000 microseconds Rate-1-50 pulses per secondRate-1-50 pulses per second

Audio Amplifier- allows the practitioner Audio Amplifier- allows the practitioner to hear the electrophysiological to hear the electrophysiological activity, necessary for assessment via activity, necessary for assessment via needle electromyograpyneedle electromyograpy

Physiology- action potential, if it is a Physiology- action potential, if it is a threshold response, depolarization threshold response, depolarization occurs and the potential is occurs and the potential is propagated in both directions: (TENS propagated in both directions: (TENS Unit)Unit)

OrthodromicOrthodromic Antidromic Antidromic

Sensory Sensory Ascending, distal to proximal. Sensory Ascending, distal to proximal. Sensory

response is dependent on the number of response is dependent on the number of axons conducting and the speed at which axons conducting and the speed at which they conduct.they conduct.

PhysiologyPhysiology

Motor Motor Descending, proximal to distal. Motor Descending, proximal to distal. Motor

response is dependent on the number of response is dependent on the number of axons conducting and the speed at which axons conducting and the speed at which they conduct but may also be affected by a they conduct but may also be affected by a disorder or dysfunction of the myoneural disorder or dysfunction of the myoneural junction of the muscle itself.junction of the muscle itself.

Motor unitMotor unit a nerve fiber and all the muscle fibers it a nerve fiber and all the muscle fibers it

innervatesinnervates

Physiology Physiology

Neuromuscular junctionNeuromuscular junction(motor end (motor end plate or myoneural junction) plate or myoneural junction) site where nerve fiber (axon) site where nerve fiber (axon)

communicates with individual muscle communicates with individual muscle fibers.fibers.

Physiology Physiology

Synaptic transmissionSynaptic transmission For information to cross the synaptic cleft For information to cross the synaptic cleft

in the CNS or neuromuscular junction, a in the CNS or neuromuscular junction, a chemical mediator (transmitter) has to be chemical mediator (transmitter) has to be released from the knobs located at the released from the knobs located at the end of the presynaptic fiber by the action end of the presynaptic fiber by the action potential. Process triggered by calcium potential. Process triggered by calcium ions. Conduction can generally only occur ions. Conduction can generally only occur in one direction. The transmitter attaches in one direction. The transmitter attaches to the receptor sites on the post to the receptor sites on the post junctional membrane which increases junctional membrane which increases permeability to sodium and potassium.permeability to sodium and potassium.

PhysiologyPhysiology

Evaluation of Evoked Evaluation of Evoked PotentialsPotentials

Sum total of fibers Sum total of fibers recorded, measured from recorded, measured from baseline (isoelectric line), baseline (isoelectric line), to negative peak (SNAP, to negative peak (SNAP, CMAP)CMAP)

AmplitudeAmplitude

AmplitudeAmplitude Considered a measure of the number Considered a measure of the number

and the synchronicity of axon firing. and the synchronicity of axon firing. A decrease in amplitude is associated A decrease in amplitude is associated

with a loss of functional axons. This with a loss of functional axons. This may be seen initially with trauma, but may be seen initially with trauma, but will occur over time as a result of will occur over time as a result of pronounced or chronic compression, pronounced or chronic compression, or from chronic inflammation.or from chronic inflammation.

AmplitudeAmplitude Stimuli applied and recorded over a Stimuli applied and recorded over a

significant distance may result in a significant distance may result in a reduced amplitude due to normal reduced amplitude due to normal variation in axonal conduction rates variation in axonal conduction rates and is termed “temporal dispersion”. and is termed “temporal dispersion”.

An increased duration and/or rise An increased duration and/or rise time may also result in a reduced time may also result in a reduced amplitude, as will conduction block.amplitude, as will conduction block.

a neuropraxic condition in a neuropraxic condition in which there is a mechanical which there is a mechanical blocking of all or a portion of blocking of all or a portion of the axons, resulting in a drop in the axons, resulting in a drop in amplitude when recording a amplitude when recording a stimulus that passes through stimulus that passes through the site but in which case there the site but in which case there is no actual axonal death and is no actual axonal death and the axons distal to the site of the axons distal to the site of compromise conduct normally. compromise conduct normally.

ConductionConduction BlockBlock

ConductionConduction BlockBlock This is the common occurrence This is the common occurrence

when your foot goes to sleep when your foot goes to sleep after crossing your legs. It can after crossing your legs. It can be differentiated from axonal loss be differentiated from axonal loss by stimulating and recording by stimulating and recording distal to the site of the distal to the site of the compromise, in which case the compromise, in which case the amplitude will return to normal.amplitude will return to normal.

Rise TimeRise Time

Measured in milliseconds from the Measured in milliseconds from the initial deflection to negative peak. initial deflection to negative peak.

A prolonged rise time is indicative A prolonged rise time is indicative of slowing of a portion of the axons of slowing of a portion of the axons relative to the others and if severe relative to the others and if severe enough may result in a reduced enough may result in a reduced amplitude.amplitude.

Rise TimeRise Time

The rise time will vary The rise time will vary slightly due to normal slightly due to normal variability in conduction variability in conduction rates. A prolonged rise time rates. A prolonged rise time is a result of asynchronous is a result of asynchronous axonal conduction rates or axonal conduction rates or muscle fiber firing rates.muscle fiber firing rates.

DurationDuration

Time (milliseconds) of the Time (milliseconds) of the initial negative deflection to initial negative deflection to the return of the positive the return of the positive phase to the isoelectric line. phase to the isoelectric line.

Generally biphasic in shape Generally biphasic in shape (negative then positive).(negative then positive).

LatencyLatency time lapse from stimulation to time lapse from stimulation to

response. response. A measure of conduction speed, time A measure of conduction speed, time

required for the impulse to go from the required for the impulse to go from the stimulator to the recording electrodes. stimulator to the recording electrodes.

An increased latency indicates the An increased latency indicates the conduction is slowed and is associated conduction is slowed and is associated with demyelination of the nerve (one with demyelination of the nerve (one of the first signs of compromise). of the first signs of compromise). Numbers are compared to established Numbers are compared to established norms and to the contralateral norms and to the contralateral extremity, and other ipsilateral nerves extremity, and other ipsilateral nerves over the same distance.over the same distance.

SDL (sensory distal latency)SDL (sensory distal latency)

refers to the latency of the distal refers to the latency of the distal portion of a sensory nerve and is portion of a sensory nerve and is measured to the negative peak.measured to the negative peak.

MDL (motor distal latency)MDL (motor distal latency) refers to the latency of the distal portion of refers to the latency of the distal portion of

a motor nerve. a motor nerve. Motors will generally be slower than Motors will generally be slower than

sensories due to the impulse having to sensories due to the impulse having to cross the myoneural junction. Due to the cross the myoneural junction. Due to the inability to measure the time required to inability to measure the time required to cross this junction velocities are not cross this junction velocities are not calculated for the distal segment of the calculated for the distal segment of the motor nerves. Motor latencies are motor nerves. Motor latencies are measured to the initial negative deflection.measured to the initial negative deflection.

Nerve Conduction VelocityNerve Conduction Velocity

speed of propagation of an speed of propagation of an action potential along a nerve. action potential along a nerve.

Represents conduction velocity Represents conduction velocity of fastest fibers and is of fastest fibers and is expressed in m/sec. expressed in m/sec. (distance (distance divided by the time) divided by the time)

Nerve Conduction VelocityNerve Conduction Velocity

Velocities that are reduced are Velocities that are reduced are associated with demyelination of associated with demyelination of the nerve.the nerve.

Velocities are only accurate over Velocities are only accurate over distances greater than 10 cm. distances greater than 10 cm.

Velocities are utilized on more Velocities are utilized on more proximal segments of a nerve in proximal segments of a nerve in place of latencies, due to variability place of latencies, due to variability in arm/leg length. in arm/leg length.

Conduction velocities are Conduction velocities are dependent ondependent on

diameter of the axon- lower diameter of the axon- lower internal resistanceinternal resistance

myelin thicknessmyelin thickness internodal distanceinternodal distance temperature (fingers>31ºC and temperature (fingers>31ºC and

toes>29 ºC) toes>29 ºC) Age (<5y/o, >70y/o)Age (<5y/o, >70y/o)

Changes in conduction velocity may be a Changes in conduction velocity may be a result of demyelination and result of demyelination and remyelinationremyelination

DemyelinationDemyelination Disturbances of Schwann cells causing a Disturbances of Schwann cells causing a

decrease in the thickness of the myelindecrease in the thickness of the myelin Sodium channels concentrated at the Sodium channels concentrated at the

Nodes of Ranvier are redistributed Nodes of Ranvier are redistributed throughout the area of demyelinationthroughout the area of demyelination

Conduction changes from saltatory to Conduction changes from saltatory to continuous (Eddy currents) leading to continuous (Eddy currents) leading to slower nerve conduction velocity (NCV)slower nerve conduction velocity (NCV)

RemyelinationRemyelination As remyelination occurs, the NCV As remyelination occurs, the NCV

increasesincreases

ShapeShape Motor and sensory potentials are generally Motor and sensory potentials are generally

biphasic;negative then positive. biphasic;negative then positive.

A triphasic response with an initial positive A triphasic response with an initial positive deflection is usually present when deflection is usually present when recording from the abductor hallucis brevis recording from the abductor hallucis brevis but in other nerve studies may be but in other nerve studies may be eliminated by improved accuracy in eliminated by improved accuracy in placement of the recording electrodes or placement of the recording electrodes or swinging the anode of the stimulator off swinging the anode of the stimulator off the nerve. the nerve.

Performance of the Performance of the ExamExam

A thorough history is essential.A thorough history is essential.

The patient should be positioned The patient should be positioned comfortably on a wooden (non-comfortably on a wooden (non-metal) plinth. If this is not possible metal) plinth. If this is not possible unplug any power sources to the unplug any power sources to the table/bed and position the patient table/bed and position the patient so that they are unable to come in so that they are unable to come in contact with any metal components.contact with any metal components.

Skin should be cleaned with alcohol Skin should be cleaned with alcohol prior to application of the electrodes prior to application of the electrodes and mild abrasion of the skin may and mild abrasion of the skin may reduce impedance.reduce impedance.

All electrodes and stimulator probes All electrodes and stimulator probes should be washed with warm soapy should be washed with warm soapy water following each use.water following each use.

Nerve conduction units should have a Nerve conduction units should have a safety check and be calibrated safety check and be calibrated annually.annually.

Have emergency procedures in place.Have emergency procedures in place.

Always place the ground on the same side of Always place the ground on the same side of the body as the recording electrodes and the the body as the recording electrodes and the stimulus application.stimulus application.

Patients with cardiac pacemakers should not Patients with cardiac pacemakers should not be stimulated near the trunk and with older be stimulated near the trunk and with older pacemakers the referring physician should pacemakers the referring physician should be consulted prior to performance of the be consulted prior to performance of the exam.exam.

  

Consult with referring physician prior to Consult with referring physician prior to performance of an exam on any patient with performance of an exam on any patient with metal catheters or wires.metal catheters or wires.

PrecautionsPrecautions

TemperaturesTemperatures Room temperatures should not be Room temperatures should not be

below 25below 25°C°C..

Temperature of the patient should be Temperature of the patient should be monitored and finger temps should monitored and finger temps should not drop below 31not drop below 31°C °C and temps of and temps of the toes should not drop below 29the toes should not drop below 29°C°C. .

Though correction factors may be Though correction factors may be utilized every attempt should be utilized every attempt should be made to increase the patients body made to increase the patients body temperature through the use of heat temperature through the use of heat sources, activity, etc.sources, activity, etc.

Latencies generally increase .2 ms for Latencies generally increase .2 ms for each one degree drop in temperature.each one degree drop in temperature.

Velocities generally decrease 2 ms for Velocities generally decrease 2 ms for each one degree drop in temperature.each one degree drop in temperature.

Nerve conduction velocities will be Nerve conduction velocities will be slower in children below age 7 and in slower in children below age 7 and in persons greater than 70.persons greater than 70.

Axonal DegenerationAxonal Degeneration

Several changes can occurSeveral changes can occur1.1. Axonotmesis/second degree of Axonotmesis/second degree of

some or all fiberssome or all fibers

2.2. Neurotmesis/third degree to Neurotmesis/third degree to fifth degreefifth degree

Reinnervation Secondary Reinnervation Secondary to Axonal Sprouting:to Axonal Sprouting:

Sprouting re-adoption is a Sprouting re-adoption is a process that is continually process that is continually occurring in a normal stateoccurring in a normal state

1.1. Undamaged axonsUndamaged axons

2.2. Occurs in a few days after injuryOccurs in a few days after injury

3.3. Age relatedAge related

4.4. Earlier in fast twitch (type II)Earlier in fast twitch (type II)

Axonal RegenerationAxonal Regeneration

If the cell body does not die, then If the cell body does not die, then regeneration in the form of nerve sprouts regeneration in the form of nerve sprouts growing from the proximal stump may growing from the proximal stump may begin as early as 24hrs post injury.begin as early as 24hrs post injury.NeurotropismNeurotropism

1.1. Process of stimulating growthProcess of stimulating growth2.2. Poorly understoodPoorly understood3.3. Multiple factors including NGF, hormones Multiple factors including NGF, hormones

and electrical stimulation have been and electrical stimulation have been reported to stimulate growthreported to stimulate growth

4.4. Axonoplasmic flow is very importantAxonoplasmic flow is very important

C.C. Regeneration Regeneration 1.1. Begins within 24hrsBegins within 24hrs2.2. Requires weeks to monthsRequires weeks to months3.3. Average 2-3 mm/dayAverage 2-3 mm/day4.4. 0.25 mm/day through scar0.25 mm/day through scar5.5. Slower after sutureSlower after suture6.6. Faster after crushFaster after crush7.7. Age related Age related

Axonal RegenerationAxonal Regeneration1.1. No preference for fascicular tissueNo preference for fascicular tissue

a.a. Motor may enter sensory endoneurial tubesMotor may enter sensory endoneurial tubesb.b. Sensory may enter motor endoneurial tubesSensory may enter motor endoneurial tubesc.c. Motor may enter the wrong motor Motor may enter the wrong motor

endoneurial tubeendoneurial tube

Aberrant ReinnervationAberrant Reinnervation1.1. Phrenic axons to upper extremitiesPhrenic axons to upper extremities2.2. Ballistic movements (type II fibers only) Ballistic movements (type II fibers only)

H ReflexH Reflex

BackgroundBackground The reflex was 1The reflex was 1stst described by described by

Hoffinan in 1918 (Tibial H Reflex)Hoffinan in 1918 (Tibial H Reflex) Magladery and McDougal expanded Magladery and McDougal expanded

Hoffinan’s work, and in their published Hoffinan’s work, and in their published work in 1950 they honored Hoffinan by work in 1950 they honored Hoffinan by adding the “H” to the term reflex adding the “H” to the term reflex

In 1974 Braddom and Johnson In 1974 Braddom and Johnson provided “normal” data on latencies provided “normal” data on latencies and a standardized technique and a standardized technique

AnatomyAnatomyIa afferent fibers from the muscle Ia afferent fibers from the muscle

spindle to the anterior horn cell spindle to the anterior horn cell synapse with the alpha motor neuron synapse with the alpha motor neuron from the anterior horn to the musclefrom the anterior horn to the muscle

It is the electrophysiologic It is the electrophysiologic equivalent of the monosynaptic equivalent of the monosynaptic (muscle) stretch reflex, however, the (muscle) stretch reflex, however, the muscle spindle is bypassed muscle spindle is bypassed

Characteristics of Normal H Characteristics of Normal H ReflexReflex It is a late response It is a late response It usually occurs first, then the M responseIt usually occurs first, then the M response The amplitude of the M wave is larger than The amplitude of the M wave is larger than

the amplitude of the H responsethe amplitude of the H response The H reflex is elicited with submaximal The H reflex is elicited with submaximal

intensity and inhibited by supramaximalintensity and inhibited by supramaximal The H reflex is supressed with a stimulation The H reflex is supressed with a stimulation

rate over 2ppsrate over 2pps With repetitive stimulation, successive H With repetitive stimulation, successive H

responses remain relatively constant in responses remain relatively constant in shape and latencyshape and latency

F WaveF Wave An F wave results when an An F wave results when an

antidromic motor fiber impulse antidromic motor fiber impulse physiologically rebounds off the physiologically rebounds off the anterior horn cell and anterior horn cell and orthodromically returns to cause orthodromically returns to cause muscle contraction. First named muscle contraction. First named and reported the F wave in the and reported the F wave in the 1950s and originally interpreted as 1950s and originally interpreted as a reflex. It was finally determined a reflex. It was finally determined it was a result of antidromic motor it was a result of antidromic motor impulses and not a refleximpulses and not a reflex

Characteristics of the F Characteristics of the F wavewave

The M response occurs first The M response occurs first and is much largerand is much larger

The latency variesThe latency varies They only occur with They only occur with

suprmaximal stimulisuprmaximal stimuli An interruption of the posterior An interruption of the posterior

roots (sensory) will not abolish roots (sensory) will not abolish itit