Group members:
•Kanchan Sharma
•(BPT 4TH YEAR, AMITY UNIVERSITY)

 Electrodiagnosis is the field of study that, by employing the
science of electrophysiology, uses electrical technology to
study human neurophysiology.
 Information needed to answer any questions regarding the
nerve injury, muscle injury, muscle disease, localization, and
prognosis can be thus obtained through the help of
electrodiagnostic testings.
 The information collected through the testing helps to focus
treatment on the exact site of injury.
 In addition to using a patient's history, physical examination
and imaging results, the clinician can obtain information
about the functional status of various parts of the nervous
system by monitoring its electrical activity. This is
accomplished via a variety of Electrodiagnostic tests like:
Electromyography (EMG)
Nerve conduction velocity (NCV)
Evoke potentials (EP)

 One should be well aware of the normal neurophysiologic
function of the nervous system.
 Electrical signals are generated in the brain, pass through the
spinal cord and travel into the peripheral nervous system.
 These signals are carried down the nerve to the synaptic
cleft, where a chemical release of acetylcholine crosses the
synaptic cleft to create an electrical discharge in the muscle.
This electrical signal causes the muscle to contract.
Neurodiagnostic testing bypasses the brain by delivering an
electrical charge to the patient.
 The equipment then is used to measure several aspects of the
body's response to that signal to determine whether it is
functioning properly.
 Location and degree of the injury, acuity, prognosis, and (in
some cases) specific diagnosis can also be determined by the
electrodiagnostic testing.

Electromyography is the study of a motor unit activity.
 A technique by which the action potentials of contracting
muscle fibres and motor units are recorded and displayed.
 Recording the EMG requires a three phase system:
An input phase: when the electrodes pick up electrical
potential from contracting muscle
A processor phase: In this the small electrical signal is
amplified
An output phase: electrical signal is converted to visual or
audible signals so that data can be displayed and analysed.
 An electrode is a transducer, a device for converting one form
of energy into another.
 The distance of recording electrodes from the muscle fibre
determines the rise time and fall time of muscle fibres.

The electrodes are of the following types:
 Surface electrodes
 Needle electrodes
 Finewire indwelling electrodes
 Intracellular electrodes
 Multilead electrode etc.
Technique of EMG recording:
It includes the following steps:
1. Patient is asked to relax and the needle is inserted inside
the muscle, simultaneously spontaneous burst of potential
is observed.
2. The insertion activity is observed when the needle breaks
the fibre membrane. The equipment of EMG recording is set
up at sweep speed 5-10 ms/div; amplification 50 mv/divison
for studying spontaneous activity and 200 microvolt for
motor unit potentials and filter selting 20-10000 Hz.
3. The duration of MUP’s should be measured at a gain of
100microvolt/division and sweep speed of 5 ms/div and low
filter at 2-3 Hz

MOTOR UNIT ACTION POTENTIAL:
 It is the sum of electrical potential of the muscle fibres
present in the single motor unit, having the capabilities of
being recorded by he electrodes.
 The normal motor unit action potential depends upon on the
given five factors that is amplitude, duration, shape, sound
and frequency.
 In the normal muscle, the amplitude of a single motor unit
action may range from 300 mV to 5mV from peak to peak.
The total duration measured from initial baseline will
normally range 3 to 16 m-sec.
 The duration of the motor unit action potential normally
varies from 5 to 15 ms depending upon the age of the
patients, muscles examine and temperature.
 Rise time of MUAP: duration from the initial positive two
subsequent negative peak. It is an indicator of the distance of
needle electrode from the muscle fiber. A greater rise time is
attributed to the resistance and capacitance of the
intervening tissue.

 Amplitude of MUAP: It is measured from peak to peak . It
depends upon size and density of muscle fiber, synchrony of
firing, proximity of needle to muscle fiber, age of subject,
muscle examine and muscle temperature. Decrease in the
muscle temperature results in the higher amplitude and
longer duration of MUAP.
 Phase of MUAP: portion of MUAP between departure and
return to the base line. It can be monophasic, diphasic or
polyphasic depending on the number of phases obtained.

 Artifacts: Any unwanted electrical activity that arises outside
of the tissues being examined. These artifacts can be of
sufficient voltage to distort the output signal markedly.
They are of two types:
1: Movement Artifacts
2: Power Line Interference
 Cross-Talk: Another important consideration is the ability of
electrodes to record activity selectively from a single muscle.
Because of volume conduction, electrical activity from nearby
contracting muscles, other than the muscle of interest, may
reach the electrodes and be processed simultaneously.
There is no way to distinguish this activity by looking at the
output signal.
Careful electrode placement and spacing and choice of size and
type of electrode will help control such cross-talk or electrical
overflow.

 Amplifier System: Before motor unit potential can be
visualized, it is necessary to amplify small myoelectric signals.
An amplifier converts the electric signal large enough to be
displayed.
Differential amplifier: The electric potential is composed of
the EMG signal from muscle contraction and unwanted noise
from the static electricity in the air and power lines. To control
for the unwanted part of the signal , the differential amplifier
is used, as noise is transmitted to the amplifier as a common
mode signal when the difference of potential is reduced at both
the ends, the noise being cancelled out both the ends of
amplifier.
 Common mode rejection ratio: CMRR is a measure of how
much the desired signal voltage is amplified relative to the
unwanted signal.
A CMRR of 1000:1 indicates that the wanted signal is amplified
1000 times more than the noise. It can also be expressed
100000:1. The higher is this value , the better it is.

Abnormal spontaneous potential:
As a normal muscle at rest exhibits electrical silence, any
activity seen during the relax state is considered as abnormal.
The common abnormal spontaneous activities are:
1.Fibrillation Potential
2. positive sharp waves
3. fasciculation potential
4. repetitive discharges
 Fibrillation potential: fibrillations are spontaneous occurring
action potential from single muscle fibre.
Fibrillation potential is seen in the denervated muscle as they
give spontaneous dischages due to circulating acetyle choline.
Fibrillation potential are classically indicative of LMN
disorders such as peripheral lesion, anterior horn cell disease,
radiculopathy and polyneuropathies with axonal degeneration.

 Positive Sharp Waves: Found in denervated muscles at rest
and accompanied by fibrillation potentials. These are
recorded as a biphasic with a sharp initial positive deflection
followed by slow negative phase. Positive sharp waves are
seen in primary muscle disease like muscular dystrophy,
polymyositis but sometimes also seen in UMN lesions.
 Fasciculation potential: random twitching of muscle fiber
or a group that may be visible through skin. These are
spontaneous potentials (may be biphasic, triphasic or
polyphasic) seen with irritation or degeneration anterior
horn cell, nerve root compression and muscle spasm or
cramps.
 Repetitive discharges: also called “bizarre high frequency
discharges”. These are characterized by an extended train of
potentials of various forms. These are seen with lesions of
the anterior horn cells, peripheral nerves and with the
myopathies.

 It is the application of electrodiagnostic testing to the CNS.
These tests are clinically useful means to do the following:
1. demonstrate abnormal sensory function when the
neurologic examination results do not reveal abnormalities.
2.reveal clinically unsuspected pathology when demyelinating
diseases are suggested.
3. objectively monitor a patient’s progress or deterioration
over time.
 The test includes a number of ways to perform Evoke
potentials like:
1. somatosensory EP
2. visual EP
3. Brainstem auditory EP
4. Dermatomal and myotomal EP

Somato-sensory EP: Stimulation
occurs at extremity, recorded
on scalp near sensory cortex.
Useful in localizing demyelinating
diseases such as MS, determine
level of coma and to evaluate for
brain death.
Visual EP: A photoelectric
checkboard-pattern flash is used
to stimulate the optic nerve
which is recorded on the cortex
and is then arrived at occiput,
near the visual centres.

Brainstem auditory EP:
The auditory click is used to
stimulate cochlear nerve
and response is collected over
the cortex area.
Dermatomal EP and
Myotomal EP: The stimulation
occurs along the dermatome
or myotome with it’s recordings
at the cortex.

ROLE OF Evoke Potentials IN SURGERIES:
It helps in detecting any interruptions in the signals across
the spinal cord while the spinal surgeries (for eg; scoliosis)
are progressed.
The electromyographer repeatedly performs the somato-
sensory evoke potentials and informs the surgeon about the
interruptions, so that needed interventions can be taken,
thus, permanent injury can be prevented.


NCV test determines how quickly electrical signals move
through a particular peripheral nerve. It also sometimes known as
NERVE CONDUCTION STUDY and is used in the diagnosis of nerve
damage or nerve dysfunction.
Purpose of NCV test :
• The peripheral nerves are the nerve outside the brain and the
spinal cord. These nerves helps control the muscles and
experience important senses.
• Healthy nerves send electrical signals more quickly and with
greater strength than damaged nerves.
For this reason, NCV is helpful in determining the existence,
type, and extent of nerve damage in a patient.
• The NCV test allows the physician to tell the difference between
an injury to the nerve axon and an injury to the myelin sheath-
the protective covering surrounding the nerve.

 It is also useful for telling the difference between a nerve
disorder and a condition where nerve injury has affected
the muscles.
Being able to make these distinctions is important for
diagnosis and for determining an appropriate course of
treatment.

When is this test necessary:
 This test is useful for diagnosing a variety of different
muscular and neuromuscular disorders.
 A doctor may use this test if they suspect a pinched nerve.
Alternately, they may use it if they wish to check for the
presence of nerve disease.
 The test is often performed with an electromyography
(EMG), which is a test that records electrical signals
moving through the muscles.
Preparation on NCV test:
 Going into the test, it is important that the patient have a
normal body temperature. This is because a low body
temperature slows down nerve conduction.
 If the weather is very cold, for instance, the doctor may
ask the patient to sit in a warm room for a few minutes
before the test is performed.

How a NCV test is performed:
 Flat, patch-style electrodes are placed on the skin at
intervals over the nerve that is being examined.
 These electrodes give off low- intensity electrical impulses,
which stimulate the nerve.
 This stimulation may feel like a slight electric shock, though it
is not particularly painful.
 This impulses produced by this electrical current are viewed
on an oscilloscope or computer screen. This monitoring system
allows the physician to determine how fast the impulses are
travelling through the nerves.

Understanding the test results:
The test may have the following outcomes:
 If the response from the electrical current is slower than
normal, this is a likely sign of damage to the myelin sheath.
 If the response shows a decreased response but with a normal
speed, there is probably damage to the nerve fiber.
The result of this test, as well as the cause of the nerve
damage, will help determine a proper course of treatment.
Possible causes for abnormal results on this test are:
1. axonopathy (damage to the nerve cell)
2. conduction block (obstacle to impulse within nerve)
3. demyelination (damage to the myelin sheath)