Needle Electromyography It is the study of electrical potentials developed in the muscle both at rest and on volition There are over 400 skeletal muscles in the body for assessment by electromyography EMG ID: 931572
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Slide1
Basic Electromyography
Slide2Needle Electromyography
It is the study of electrical potentials developed in the muscle both at rest and on volition.
There are
over 400 skeletal muscles
in the body for assessment by electromyography (EMG).
Clinical EMG involve examination of physiology / path physiology of
MU
activation and recruitment during different conditions of the muscle.
The term
motor unit action potential
( MUAP )
is used to describe the recorded
summated depolarization
of the muscle fibers belonging to
one
motor unit.
Slide3Motor unit:
A motor unit
is one anterior horn cell, its axon and all the muscle fibers innervated by that motor neuron
Slide4Benefits of EMG
Electromyography is widely used to distinguish weakness due to muscle disease/ neuropathy .
Provide neurophysiologic information about ; diagnosis, localization, nature, severity of pathology and prognosis
.
To detect the site of the lesion;
Roots, Trunks, Cords & peripheral nerves
To know the extent of the lesion;
axonal lesion/ conduction block
To detect & follow up signs of reinnervation
Slide5Needle Electrodes
Monopolar,
Standard / coaxial concentric,
Single-fiber electrode,
Bipolar concentric electrode
Recording Electrodes
Slide6Types:
Disc
Cup
Ring
Surface Electrodes
Slide7Needle electrodes in EMG pick up individual motor unit action potentials generated within a restricted radius of the recording tip.
. Needle Electrodes
Slide8EMG tests :
Clinical EMG consists of application of the following steps
Insertion activity:
insertion of the electrode into the target muscle.
Activity at rest:
search for spontaneous activity .
On minimal volition: MUP analysis/ character
Interference pattern:
when the patient is exerting a maximal effort to contract the muscle .
Turn/ Amplitude analysis.
Slide9Insertion activity:
They are discharge potentials resulting from the
mechanical disruption
of the
muscle cell membrane
by the tip of the needle.
Normally
→
they consist of
brief
,
transient
muscle action potentials in the form of spikes.
They remain only for
few
seconds (with duration of 75-100 ms).
They
disappear
immediately when needle movements stop.
They may be reduced, when the muscle tissue has been replaced by fibrosis or necrosis.
They
increased in → acute polymyositis and myotonic disorders due to hyperirritability of muscle cell membrane.
Slide102-Examination of muscle at rest
:
Healthy muscle at rest is clinically silent as soon as needle movement stops.
Spontaneous activity
:
They are present at rest with complete muscle relaxation .
Slide11End-plate activities (
EPPs )
They are
normal
spontaneous activities.
It is recorded when the needle is
in the vicinity of a motor end-plate
.
Patient usually complain of pain at this site of insertion
They can be :
**
Monophasic (end-plate noise)
→ * potentials of low amplitude and short duration. * cause a thickened baseline appearance. * give a typical sea shell noise.
**
Biphasic
(
end-plate spikes
)
→ * Irregular biphasic spikes potentials. * 100-300 µV amplitude - short duration - 20-150 Hz..
* The initial deflection is negative.
Slide12Fibrillation potentials (Fibs
) :
a
single muscle fiber
fires autonomously. They are bi or triphasic, of small amplitude (e.g. 200 or 300 microV), sound like
raindrops.
Positive sharp waves:
Consist of a primary positive (downward deflection) followed by a return to baseline. Duration between 10-30 msec.
To differentiate FPs from EPPs
: FBS fire regularly , at lower frequency (1-20 impulse /second), have an initial positive deflection, triphasic and not associated with visible muscle contraction
Slide13The Fibrillation Potential
Of
short
duration (<3 ms).
Of
low
amplitude (<300 µv).
Occur in
semi rhythmical
runs (2-30 Hz).
The initial deflection is
positive.
Develop two to three weeks after the neuron or axon has been damaged.Develop earlier in muscles nearer to the neural axis than those in the distal part of the extremities.
Decrease with beginning of
reinnervation
and eventually disappear as reinnervation is successfully completed.
Slide14Positive Sharp Wave
Very
sharp positive
deflection followed by a slower
long negative
phase.
The
positive
phase may reach up to
1 mV
in amplitude and can last up to 50 msec
. duration.The
negative phase may last up to 100 msec. duration or more. Usually, they are rhythmic discharge.
Slide15Other pathological spontaneous activity
Slide16Fasciculation potential
A spontaneous
irregular
discharge of
single motor unit
in a random fashion.
They correspond to
visible twitches
in the muscles.
It can be:
*
Benign (monophasic, diphasic or triphasic )potentials as normal motor units. ( Fatigue or muscle cramps ).
* Malignant highly complex polyphasic potentials as neurogenic motor units. ( Anterior horn cell disease - chronic neuropathies – radiculopathies ).
Slide17Complex repetitive discharges (CRDs):
(
High frequency discharges - Bizarre repetitive potentials )
They represent
irritation
of a group of muscle fibers
with an affected area of the muscle electrically stimulating adjacent muscle fibers and so on.
They repeat in a regular pattern starting and ending abruptly.
Usually of
low
amplitude and
short
duration with firing frequency between 5-150 Hz.
The amplitude of which is between 50 and 500 micro volts.
Slide18CRDs
Slide19Complex repetitive discharges
(CRDs):
They are nonspecific potentials seen in:
*
Neuropathic diseases
(
chronic root lesions - peripheral neuropathies - motor neuron diseases - nerve regeneration
).
*
Myopathic conditions
( early stages of Duchenne muscular dystrophy ). *
Polymyositis.
*
Myxedema.
Slide20Myotonic discharges
:
This sustained run of spike potentials/PSW seen at rest and begins at high frequency and then slowly drops in frequency, producing so called
dive-bomber
sound on audio. *They represent
action potentials of muscle fibers
firing in a prolonged fashion i.e. failure of relaxation.
*They fire at a variable rate with
a waxing and waning appearance.
*Myotonic discharges are seen in
myotonia congenita, myotonic dystrophy, hyperkalemic periodic paralysis.
Slide21Myotonic discharge
Both positive sharp waves and negative spikes typically wax and wane in amplitude over the range of 10 µV to 1 mV often, though not always, varying inversely with the rate of firing.
Their frequency may increase or decrease within the range of 50–100 impulses per second, giving rise to a characteristic noise over the loud-speaker that is reminiscent of an accelerating or decelerating motorcycle or chain saw.
Slide22Myokymia
Abnormal
rhythmic MU contraction
.
Bursts of discharges from a single MU containing 2-4 spikes firing at rate up to 40 discharge /second.
Associated
with “wormlike” movements
.
This bursts are due to ectopic generation of APs in demyelinating nerve fiber.\myokymia involving face muscles is most commonly seen in patients with
brain stem glioma, multiple sclerosis
.Myokymia in the limb muscles is most often related to chronic inflammatory polyradiculopthy. Myokymic discharges also favor certain chronic neuropathic processes, such as Guillain Barre syndrome. Hyperventilation induces hypocalcemia, which in turn amplifies axonal excitability and myokymic bursts, generated ectopically in demyelinated motor fibers.
Slide23Neuromyotonia
Neuromyotonia /
pseudomyotonia
, describe continuous muscle fiber activity of peripheral origin. These syndromes probably constitute different diseases
that vary in their clinical and electrophysiological presentations despite the shared feature of sustained involuntary motor activity.
The sites of generator responsible for different discharges vary from proximal segments of the nerve to the intramuscular nerve terminals.
Excess motor unit activity remains during sleep and after general or spinal anesthesia.
Clinical examination
shows undulating movements of the overlying skin and a delay of relaxation after muscle contraction, thus the name neuromyotonia.
Needle studies demonstrate motor unit discharges with frequencies up to 300 Hz associated with a characteristic
“pinging” sound. The firing motor unit potentials decline in amplitude slowly or rapidly as increasing numbers of muscle fibers fail to follow the high rate of repetitive pattern.
Ischemia or electrical nerve stimulation provokes the high-frequency discharge. Patients respond well to treatment with phenytoin or carbamazepine, which effectively reduces involuntary movements.
Slide24Nuromyotonia
Motor unit potentials decline in amplitude slowly or rapidly as increasing numbers of muscle fibers.
.
Myokymia:
Rhythmic MU contraction
Nuromyotnia is exaggerate form of myokymia
Slide25Muscular Contraction
Striated Muscle
Peripheral
Nerve
No
Contraction
Discrete
Contraction
Moderate
Contraction
Maximum
Contraction
Motor Neuron
Motor Unit
0 MUP
1 MUP
3 MUPs
++
MUPs
Motor Unit Potentials
Slide26On minimal volition:
A motor unit
is a compound muscle fiber action potential synchronously generated in the muscle fiber of the MU overlap in time and are summated at the recording electrode.
It is considered as the
electrophysiology correlate with the contraction of MU.
Shape of MUAP
depend on the location of the electrode with respect to the active muscle fibers in the unite. with muscle contraction, a number of MUAPs are recruited.
Changes in the number of muscle fibers
→
changes in MUAP duration .
The MUAP duration is increased in neuropathy due to collateral sprouting which
↑ the number of muscle fibers / motor unit.In myopathy, duration decreases due to loss of muscle fibers
Slide27Normal MUAP:
Slide28First The patient is asked to minimally contract the muscle.
Second Components of motor unit (MUAP) to be analyzed:
Amplitude, rise time, duration, number of phases;
Slide29Parameters of normal MUAP
Amplitude
:
(
peak to peak
);
Normally
from 0.5 to 3 m.V.
* determined by: - The number and size of ms. fibers within 0.5 mm of the recording electrode.
- The proximity and size of the muscle fiber closest to the electrode.
Duration :( from first deflection of the baseline to last return to it ). * Normally between 2 and 15 ms. determined by the number of muscle fibers that are up to 2.5 mm from the recording electrode.
Number of phases
:
(
bip
h
asic or triphasic ); * determined by synchrony of depolarization of its muscle fibers.
The rise time : ( The time elapsed between the peak of the initial positive
(
down
) deflection to the
peak
of the highest
negative
(
up
) deflection
).
* determined by proximity of the needle tip to the muscle fibers of the contracting unit. * Normally between 200 and 300 µsec.
Slide30Motor Unit Potential (MUP)
7 Turns
3 Phases
6 Segments
Amplitude
Phase
Duration
Rising Time
Satellite
Turns
Baseline Crossing
Segment
Single Potential, Phases < 3
Polyphasic Potential, Phases > 3
Group of muscle fibers
generates MUPs.
Different innervation
different MUPs.
Slide31Polyphasic motor units:
Slide3232
( MUAP ) phases
It can be affected either by:
* Nerve disease
causing differential slowing in impulse conduction.
* Muscle disease
where the conduction characteristics of the muscle fibers themselves have changed.
The total number of phases is determined by
counting the number of times the components of the motor unit potential cross the baseline plus one.
Frequently, the MUAPs have a
saw tooth-like pattern
where there are
many changes of direction or
“turns”
but not actually cross the baseline, these are referred to as
serrated
MUAP.
The
percentage of polyphasic
MUAPs should be
reported for each muscle.
Slide33Analysis of the interference pattern (IP)
The IP measured by the recording needle electrode contains
→
the MUAPs of all active motor units that are within the uptake area of the recording surface.
The primary method for analysis of the IP was the visual judgment
→
(
including the amplitude and the degree of recruitment
).
The IP is reported as
→
complete or incomplete.
Slide34Pathologies in Striated Muscle
Normal
Neuropathy
Myopathy
Myasthenia
CNEMG
Same effort, same muscle,
different pathologies
Ground
Neuromuscular junction
disease.
See Decrement
Slide35Interference Pattern (IP):
Slide3636
Number of Turns (T/S)
Turns
→
number of potential reversals of more than 100 μV/ time unit (
independent of baseline
).
The number of turns is counted over a certain time unit (
turns/ second
).
The number of turns is influenced by:
* The number of motor units and the interaction between overlapping MUAPs.
* Their firing rate.
* The proportion of polyphasic MUAPs.
* ↑ noise.
The more the action potentials, the higher the number of turns.
In
neuropathies
→
decreased
numbers of turns/ second
and
increased
amplitude
In
myopathies
→
increased
numbers of turns/ second
and
reduced
amplitude.
Slide37EMG report
Selected muscle examined by concentric needle electrode.
EMG findings at rest; spontaneous activity /pathological potentials (Fibs/PSW) .
MUAP analysis.
IP……complete/reduced.Recruitment….early/late
Turn/S…..cloud method.
Provisional diagnosis
Slide38