you make the call - aanem
TRANSCRIPT
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Devon I. Rubin, MDProfessor of Neurology
Mayo ClinicJacksonville, Florida
Dr. Rubin receives royalties from AANEM and Demos on sale of educational EMG teaching CD-ROM programs
You Make the Call !!Mastering EMG Waveform Recognition
Basic
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Learning ObjectivesAfter this session, you should be able to:
• Recognize basic firing patterns of EMG waveforms
• Identify and understand the significance of spontaneous EMG waveforms
• Determine how the changes in MUPs help identify the type and length of disease process
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Recording and analyzing the electrical activity of the muscle fibers in motor
units in the muscle
Unique combination of knowledge and skill
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50 yo with an unusual sensation in his skin(Tibialis anterior)
What is the waveform?End plate spikeFibrillation potentialFasciculation potentialVoluntary motor unit potential
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Origin of EMG PotentialsSingle Muscle Fibers
Single FibersEnd plate spikesFibrillation potentialsMyotonic discharges
Groups of Fibers (different motor units)Insertion activityCRDs
Groups of Fibers (same motor unit)Fasciculation potentialsMyokymic dischargesNeuromyotonic discharges
Voluntary MUPs
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2 skills needed. . . PATTERN RECOGNITION Identifying WaveformsCategorize by pattern
SEMI-QUANTITATIONMUP Assessment
Recruitment, Size, Stability
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Pattern Recognition of EMG Waveforms
ListenFiring pattern“Sounds like . . . .”
LookConfiguration
NameFib, Endplate, etc.
Compare
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Firing Patterns of EMG Potentials
Semi-Rhythmic: (motor unit potential)I I I I I I I I I I I I I I I
Regular: linear change (fibrillation potential)I I I I I I I I I I I I
Regular: no change (complex repetitive discharge)II II II II II II II II II II II II II II II
Regular: exponential change, wax/wane (myotonic)III I I I I I I I I IIrregular: (random change) (end plate spike)I II I I I II I I I I I I I
Bursts: – Regular or semi-rhythmic (myokymic)
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You Make the CallWhat is the pattern of firing?
Regular: linear change (fibrillation potential)I I I I I I I I I I I I
Irregular: (random change) (end plate spike)I II I I I II I I I I I I I
Semi-Rhythmic: (motor unit potential)I I I I I I I I I I I I I I I
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Endplate noise
Endplate spikes
Endplate ActivityFiring pattern: irregular, rapidBiphasic - initial negativity
Irregular PatternI II I I I II I I I I I I I
Miniature end plate potentialsFiring pattern: irregular, rapid
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Fibrillation Potentials
Action potentials of individual muscle fibers in the absence of innervation
FIRING PATTERN: Regular
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Fibrillation PotentialsSpike form
Positive wave form
Regular: steady change (fibrillation potential) (0.5-15 Hz)I I I I I I I I I I I I
200
250
300
350
400
450
500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Inte
rspi
ke In
terv
al (m
s)
Sequential Spikes
Fibrillation Potential
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Potentials recorded from a single muscle fiber by two electrodes along the fiber
(The potentials are initiated by movement of electrode #1)
Electrode #1
Electrode #2 EH Lambert
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Fibrillation PotentialsAssociated Disorders
Neurogenic• Anterior horn cell disorders – e.g. ALS• Radiculopathies – “active” • Mononeuropathies – “severe”• Axonal peripheral neuropathies
Myopathic• Inflammatory (e.g. polymyositis, IBM)• Toxic myopathies (e.g. statin, hydroxychloroquine)• Muscular dystrophies• Metabolic (e.g. acid maltase)
Severe NMJ disorders• Myasthenia gravis (severe)
• LEMS
• Botulism
• Fiber necrosis• Fiber splitting• Vacuolar damage
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78 year old with leg pain
How would you interpret this study?Subacute, active L5 radiculopathyChronic (old), active L5 radiculopathyChronic (old), inactive L5 radiculopathy
Fibrillation potentials in RadiculopathiesDon’t always = “active”
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Reflects number of denervated fibers :
1+ - Persistent single trains2+ - Moderate numbers3+ - Many in all areas4+ - Completely fill baseline
Grading Fibrillation Potentials
1+
2+
3+
4+
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Fibrillation Potentials in MyopathiesMay be:• Low amplitude (tiny)• Very slow firing (<1 Hz)• In superficial layers (esp dermatomyositis)• Complex (split fibers)
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Site of Initiation
Myotonic Discharges
Regular: exponential change, wax/wane (myotonic)III I I I I I I I I I
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Myotonic DischargesAssociated Disorders
Neurogenic (Rare)• Axonal peripheral neuropathies• Severe, old neurogenic
disorders
Myopathic (Prominent)• Myotonic dystrophy (DM1/DM2)• Myotonia congenita• Paramyotonia congenita• Hyperkalemic periodic paralysis
Myopathic (Infrequent)• Polymyositis• Acid maltase deficiency • Drug - induced myotonia
(statins, colchicine)
clinical myotonia
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Fasciculation Potentials
Origin - AHC, axon, nerve terminal
FIRING PATTERN•Single, random, irregular•1 - 100 per minute
FORM•No standard configuration•Often distant
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Complex Repetitive Discharges
• Fast or slow (3 – 40 Hz)• Configuration: (3-10 spikes, stable or unstable)
Regular: fixed intervals (abrupt onset, cessation, change)II II II II II II II II II II II II II II II
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Site of Initiation
Complex Repetitive DischargeEphaptic transmission from neighboring muscle fibers
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50 uV
200 ms
Amp 1: 20-10kHzAmp 1: 20-10kHz
Record
12:33:23
Site of Initiation
Myokymic Discharges
Recurrent BURSTS (Regular or Irregular)Doublets, triplets, multipletsFiring rate within burst (5-150 Hz)*
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MyokymiaEtiologies
Focal Radiation (cranial, plexus, single nerve)
Brainstem (multiple sclerosis, glioma, syringobulbia)
Mononeuropathy (CTS), radiculopathy (isolated muscles)
ALS (5% pts, more in cranial muscles)*
Generalized Isaacs’ syndrome (VGKC)
Polyradiculopathy (AIDP, CIDP)
Episodic ataxia type 1 (VGKC α-subunit gene KCNA1 mutation)Rattlesnake envenomation
*Whaley NR. Rubin DI. Myokymic discharges in ALS: A rare electrophysiologic finding? Muscle Nerve 2010.
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Voluntary Motor Unit Potentials
Semi-Rhythmic (5-40 Hz) – Limited (10%) variationI I I I I I I I I I I I I I I
Sound: “ataxic clock”
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Normal Motor Unit PotentialRecording multiple (5-15) muscle fiber action potentials
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Normal or Abnormal ?
NeurogenicMyopathic
NMJ ?
If neurogenic:Acute
SubacuteChronic ?
Severity ?
When assessing MUPs, questions to answer . . .
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Temporal Course of MUP ChangesAcute Neurogenic Injury
Reduced Recruitment
Unstable Turns
Polyphasic, Long duration
Long duration
Normal 1 minute
1-2 months
2-6 months
> 6 months
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MUP1
MUP2MUP3
MUP4
ForceMild Moderate
Firing Rate (Hz)
0
5
10
15
20
25
MUP Recruitment
MUP1MUP2
MUP3
MUP4
ForceMild Moderate
Firing Rate (Hz)
0
5
10
15
20
25
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Normal MUP Recruitment
MUP1
MUP2MUP3
MUP4
ForceMild Moderate
Firing Rate (Hz)
0
5
10
15
20
25
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MUP1
MUP2
MUP3
ForceMild Moderate Strong
Firing Rate(Hz)
0
5
10
15
20
25
Reduced RecruitmentMUP Firing Rate is TOO FAST
Single MUs firing >20 Hz is abnormal*
*Petajan JH. Muscle Nerve 14:489-502, 1991
MUP1MUP2
MUP3
MUP4
ForceMild Moderate
Firing Rate(Hz)
0
5
10
15
20
25
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Assessing Recruitment
Recruitment Frequency
• Firing rate of 1st MUP when 2nd MUP begins to fire.
• NL < 11 Hz (exceptions: triceps, wrist/finger extensors, cranial muscles)
Recruitment Ratio
• Ratio of firing rate of fastest firing MUP to # of MUP firing at any one time
• Most limb muscles ratio < 5– 15 Hz: 3 MUP– 20 Hz: 4 MUP
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“Poor Activation”
MUP1MUP2
Force
Mild (Strong)
MUP Firing Rate
0
5
10
15
20
25
Effort PainCentral Disorder
StrokeMyelopathy
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Rapid (Early) RecruitmentAssessment is Effort-Dependent !
Recruitment frequency and ratio are normal
Multiple MUP with minimal effort (“all or none pattern”)
“. . . activation of >3 MUs with minimal effort or barely perceptible muscle contraction has been called early recruitment.”*
*Petajan JH. Muscle Nerve 14:489-502, 1991
MUP1MUP2
MUP3
MUP4
ForceMild
Firing Rate (Hz)
0
5
10
15
20
25
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Motor Unit Potential StabilityBlocking of Muscle Fibers
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Stable
Unstable
MUP Stability (Sound)
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Polyphasic MUPNeurogenic - Asynchronous Firing
+
++
=
+
Phase = Baseline crossings + 1
Polyphasic MUP = 5 or more phases<15% of MUPs in muscle
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Polyphasic MUP Myopathy
++
+
=
+
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Muscle Fiber Contributions to
MUP
Duration (2.5 mm)
Amplitude (0.5mm)
Motor Unit Territory (5-10 mm)
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Duration (ms)Time distribution of fibers
Amplitude (uV)Fiber density near needle tip
Area (uVms)Fiber density in larger pickup region
Thickness (Area/Amplitude)
Size Index [2 x log10 (Amp) + Area/Amp]
MUP Size Parameters
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MUP Upper and Lower Limits of Duration (msec, age 20)(from Buchthal 1955)
FDI 8.0 - 12.2
Deltoid 8.2 - 12.2
Triceps 9.3 - 13.9
Biceps 8.0 - 12.0
Anterior tibial 9.8 - 14.8
Vastus medialis 8.2 - 12.2
Medial gastroc. 7.5 - 11.3
Opponens 7.3 - 10.9
Peroneus longus 7.8 - 11.8
Gluteus maximus 9.6 - 14.4
Cervical PSP 8.6 - 12.8
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Normal Duration MUP (8-12 ms)
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Long Duration MUP (>12-14* ms)
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2 MUPs, Similar Duration (15 ms)
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MUP with Satellite Spike
=
+
++
=
+
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Learning Points
• Assess firing pattern of potential to determine the type of discharge
• Morphology of different waveforms can be similar
• Recruitment and MUP morphologies help determine temporal course