Electromyography (EMG) is a vital technique in the field of bioelectrical signal analysis. It involves capturing muscle activity through surface or needle electrodes for diagnostic purposes. EMG signals can be analyzed to detect various muscle conditions, such as myopathic or neuropathic lesions, using numerical parameters. The spatial frequency bandwidth of surface EMG signals is crucial for detailed muscle activity reconstruction, with appropriate inter-electrode distances being essential for accurate mapping. In the context of neuro-monitoring, EMG plays a role in intra-operative detection of adverse events and predicting postoperative outcomes, especially when used complementarily with other modalities like motor evoked potentials. Overall, EMG serves as a valuable tool for understanding muscle function, diagnosing muscle disorders, and enhancing neuro-monitoring practices
2. CONTENTS
PART B
• Components of EMG
• Voluntary/exertional activity (MUAP)
• Recruitment
• Single fiber EMG
• Jitter
• Fiber density
2
3. INTRODUCTION
• EMG is the process by which an examiner puts a needle into a
particular muscle and studies the electrical activity of that
muscle.
• This electrical activity comes from the muscle itself – no shocks
are used to stimulate the muscle.
EASY EMG: A GUIDE TO EMG AND NCS, JAY WEISS 3
4. DIFFERENCE BETWEEN EMG AND NCS
EMG NCS
Electrode is placed in form of needle
inside muscle
Surface electrodes over skin
No use of electric shocks, intrinsic
electrical activity of muscles are used
Electrical stimulus applied through
electrodes
Muscle activity measured directly and
nerve function measured indirectly
Nerve function measured directly
EASY EMG: A GUIDE TO EMG AND NCS, JAY WEISS
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5. ELECTRODIAGNOSTIC MACHINE
• Performs both EMG and NCS
• It has,
• Display system
• Electrodes
• Analysing unit
• Amplifier
• Filters
EASY EMG: A GUIDE TO EMG AND NCS, JAY WEISS
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6. ELECTRODES
EMG needs three type of electrodes,
• Needle electrodes (Active electrodes)
• Surface electrodes
• Reference electrodes
• Ground electrodes
EASY EMG: A GUIDE TO EMG AND NCS, JAY WEISS 6
7. NEEDLE ELECTRODES
Monopolar
needle
Concentric/Stand
ard needle
Bipolar needle
Stainless steel
with insulation
except distal 0.2
to 0.4mm
Stainless steel
canula with a wire
in center.
Cannula with
two steel or
platinum wires
Picks up 360
degree field (
larger potential
recorded)
Picks up 180
degree field (
lesser potential
recorded
Much smaller
area
Registers
between surface
electrode and tip
Registers between
wire and shaft
Registers
potential
difference
between two
wires
Lesser diameter-
lesser discomort
Lesser noisy Larger
diameter-
extremely
uncomfortable
EASY EMG: A GUIDE TO EMG AND NCS, JAY WEISS
7
Monopolar
Concentric
Bipolar
8. RECORDING TECHNIQUE
• Select the muscle as per diagnosis
• Instruct the patient how to contract and relax the muscle
• Identify the muscle as the patient is contracting and
relaxing
• Locate the insertion point slightly away from motor point
• Insert the needle quickly
• Sharp MUPs On minimal contraction confirm that needle is
in proper position 8
12. NORMAL INSERTIONAL ACTIVITY
• Introduction of needle into
muscle brief burst of
electrical activity
• Lasts slightly exceeding needle
movement(0.5 -1s)
• Atleast 4-6 brief needle
movements are made in 4
quadrants of each muscle
• Appears as positive or
negative high frequency
spikes in cluster
12
13. INCREASED INSERTIONAL ACTIVITY
• Lasts more than 300msec
• Increased insertional activity
may occur when there is muscle
pathology
• Presence of positive sharp waves
and sometimes fibrillation
potentials, That are apparent
only on insertion and do not
persist. 13
16. • SA generated near the NMJ
• Endplate noise (Miniature End Plate
Potential)
• Endplate spikes (End Plate Potential)
• SA generated from muscle fibers
• Fibrillation potentials
• Positive sharp waves
• Complex repetitive discharges
• Myotonic discharges
• SA generated from motor neurons
• Fasciculation potentials
• Doublets, triplets, multiplets
• Myokymic discharges
• Cramp discharges
• Neuromyotonic discharges 16
17. SPONTANEOUS ACTIVITY GENERATED
NEARBY NMJ
• END PLATE NOISE (MINIATURE END PLATE POTENTIAL- MEPP)
• END PLATE SPIKE (END PLATE POTENTIAL-EPP)
17
Normal SA
21. POSITIVE SHARP WAVES
• Recorded from muscle fibre with
unstable resting potentials
• Initial sharp positivity followed by a
long negative phase
• Amplitude 20-200 micro volt
• Few millisec- 100ms
• 1-15 Hz
• firing pattern is regular
• “Saw tooth appearance”
•Dull pop sound
21
22. MECHANISM OF FIBS AND PSW
• Denervated muscle fibre
leads to
• Hypersensitivity to Ach
• Increased no. of Ach
receptors
• Depolarisation
• Fibrillations and PSW 22
23. FIBS AND SHARP WAVES ARE SEEN IN
• 1. Neurogenic d/o – Anterior horn cell d/s, radiculopathy,
axonal neuropathy
• 2. NMJ d/o – Botulism, Myasthenia gravis
• 3. Myogenic d/o – Myositis, muscular dystrophy, trauma
• Density of fibs doesn’t correlate with degree of nerve damage
23
24. GRADING OF FIBS OR SHARP POSITIVE
WAVES
• 0 - none
• 1+ - single train of potential in atleast 2 areas
• 2+ - moderate no. of potentials in 3 or more areas
• 3+ - many fibs/sharp waves in all areas
• 4+ - full interference pattern of fibrillations/ sharp waves
24
25. COMPLEX REPETITIVE DISCHARGES
• Repetitive and synchronous firing of group of
muscle fibres
• local muscular ‘arrhythmia’
• high frequency (20–150 Hz)
• regular
• multi-serrated, repetitive discharges.
• abrupt onset and termination
• discharges identical in morphology
•Machine-like sound
• Ephaptic spread among
denervated fibers
• Initiated by pacemaker muscle
fiber
• circus movement
25
27. MYOTONIC DISCHARGES
• Action potentials of muscle fibres
firing for a prolonged period after
external excitation
• Waxing and waning of both amplitude
and frequency
• 20 to 150 Hz
• 2 types of potentials
• Positive waves
• Brief spikes
• Dive bomber sound
27
28. MYOTONIC DISCHARGES
Seen in
• myotonic dystrophy, myotonia congenita, and paramyotonia
congenita
• acid maltase deficiency, polymyositis, or myotubular myopathy
• hyperkalemic periodic paralysis
28
29. SPONTANEOUS ACTIVITY GENERATED FROM
MOTOR UNIT
• Fasciculation potentials
• Doublets, triplets, multiplets
• Myokymic discharges
• Cramp discharges
• Neuromyotonic discharges
29
30. FASCICULATIONS
• Single , spontaneous,
involuntary discharge of an
individual motor unit
• 0.1 to 10 Hz
• Random and irregular
• Not under voluntary control
•Corn popping
Seen in
• MND
• SMA
• Radiculopathies
• Polyneuropathies
• Entrapment neuropathies
30
31. DOUBLETS, TRIPLETS, MULTIPLETS
• Spontaneous MUPs that fire in
groups of 2,3 or multiple
potentials
• Occur because of
spontaneous depolarisation
of motor unit or its axon
• Seen in hypocalcemia,
hyperventilation,MND
31
32. MYOKYMIC DISCHARGES
• Spontaneous bursting
• Repetitive discharges of same
MUP
• Fixed pattern and rhythm
• Associated with “worm – like
quivering” of muscles
• “Marching soldiers/ machine
gun”
32
34. NEUROMYOTONIA
• High -frequency (150–250 Hz)
repetitive discharges of a single
MUAP
• Wane in amplitude and frequency
• Not influenced by voluntary
activity
• syndromes of continuous
motor-unit activity (CMUA)
• Potassium channel disorders
• c/c neuropathies
• Peripheral N irritation during
surgery
• Pinging sound
34
35. CRAMP DISCHARGE
• High-frequency discharges of MUAPs
• Abrupt onset and cessation
• benign (eg, nocturnal calf cramps,
post-exercise cramps)
• neuropathic, endocrinologic, and
metabolic conditions
• Salt depletion
• Hypocalcemia
• Pregnancy
• Uremia
• Myxedema
35
37. CONTENTS
PART A
• Introduction
• Differences b/w EMG and NCV
• EMG Machine and electrodes
• Recording methods and settings
• Components of EMG
• Insertional activity
• Spontaneous activity
37
38. VOLUNTARY / EXERTIONAL ACTIVITY/
MOTOR UNIT ACTION POTENTIAL (MUAP)
• AMPLITUDE
• RISE TIME
• DURATION
• PHASES
38
39. MUAP
• Occurs on voluntary
contraction
• Represents synchronous
discharge of all muscle fibres
supplied by single motor
neuron
• Yield information about
integrity of motor unit
39
40. DURATION
• Reflects the number of muscle
fibers
• It indicates the degree of synchrony
of firing among all individual
muscle fibers w length, conduction
velocity and membrane excitability
• Normal duration is 5–15
milliseconds
• long-duration MUAPs -dull and
thud
• short-duration MUAPs -crisp and
sharp
40
41. FACTORS AFFECTING DURATION
1.Number of muscle fibers in a motor unit
2. Dispersion of their depolarization over time (Temporal Dispersion)
• Longitudinal and transverse scatter of endplates (territory of the motor unit)
• Distance
• Conduction velocity
3. Synchrony of different muscle fibers in a motor unit
4. Age – increased age increased duration
5. Temperature- decreased temp increased duration
6. Muscle studied- MUAP is shorter in duration for proximal and bulbofacial
muscles than distal muscles.
41
43. AMPLITUDE
• 100 μV -2 mV
• reflects only those few fibers
nearest to the needle
• Factors associated with
increased amplitude
• proximity of the needle
• number and diameter
of muscle fibers
• synchronized firing
43
45. PHASES
• Phase – portion of MUP b/w departure and return to baseline
• Measure of how synchronously muscle fibers in a motor unit
fire
• Inverted triphasic potential ( + - + )
• MUP with > 4 phases – Polyphasic potential
• Turns –directional changes without crossing the baseline
• Polyphasia & turns - “desynchronization”
45
46. RISE TIME
• Duration from initial +ve to
subsequent-ve peak
• Indicator of distance of needle
electrode from MF
• Slow rise time – Resistance of
intervening tissue
• An acceptable rise time is 0.5
milliseconds or less
46
48. RECRUITMENT
• A contraction becomes stronger in two ways: the firing motor
units
• Increase their rate of firing
• Additional motor units commence firing
• Analysis should begin with the patient being told to think about
contracting the muscle being analyzed.
• Observe for the firing of a single MUAP.
• It usually begins to fire at 2–3 Hz in an irregular pattern. 48
49. • Normally the motor unit will fire in a regular pattern at about 5Hz. At around 10 Hz another
MUAP will be recruited to fire.
• The new motor unit (MU) will initially fire at about 5 Hz.
• The normal firing rate of most motor units, before additional units are recruited, is 10 Hz.
• To calculate the firing rate of the MU, note how many times a MU with an identical
morphology repeats across a screen set at 100 msec/screen (sweep speed of 10
msec/division).
• Multiply that number by ten to get the motor unit firing per 1000 msec or one second.
• Hz indicates cycles per second.
49
50. ALTERED RECRIUTMENTS
NEUROPATHIC RECRUITMENT
• In severe neuropathic lesions, when there are
few functional motor units, we can see motor
units firing at 30 Hz before a second motor unit
in that area is recruited
• Seen in
• Neuropathies
• Radiculopathies
• Motor neuron disease
• Nerve trauma
• Few motor units fire at an increased rate
MYOPATHIC RECRUITMENT
• Large number of motor units are ‘recruited’ for
a minimal contraction.
• Individual muscle fiber contribution to each
motor unit is reduced
• Since myopathic motor units cannot increase
their force output, they quickly recruit
additional motor units to increase the force of a
contraction.
50
51. SINGEL FIBER EMG
• Method of recording action
potential of a single muscle
fiber
• Selectivity in SFEMG is
achieved by
• Small recording area
• Setting a low frequency filter
• Filter setting is 500 Hz – 10
kHz
• Inserted at 20-30 degree to
skin
• Closer the needle to MF,
higher the amplitude and
shorter the rise time
• EDC, Frontalis, Biceps, I DO,
Tib. Ant – MC used
51
52. JITTER
• SF needle usually records from SF
• Possible to position the needle to record
from 2 or more MF of same motor units
• A pair of SF potential
• Triggering potential
• Slave potential
• Time interval between two potential varies
from one discharge to another
• This interpotential variability is known as
JITTER
52
53. FIBER DENSITY
• Refers to number of fibers from one motor unit that is with in a
radius of about 300 micrometer square of single fibre needle
• Nl fibre density 1.2- 1.8
• Increased fibre density – manifest early reinnervation
53
54. SFEMG IN NEUROLOGIC DISEASES
SFEMG is helpful in
• Neuromuscular transmission disorders
• Neuropathies
• Myopathies
54
55. Neurogenic transmission disorders
• Jitter – increased
• Fiber density – normal
Neurogenic disorders
• Jitter – increased
• Fiber density – increased
Myopathies
• Jitter – increased / decreased
• Fiber density – increased
55