EMG Review Final Vandersluis

7/30/2019 EMG Review Final Vandersluis

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Test question

Typical EMG findings in radiculopathy include

a) Low cmap and sensory responses; delayed / absent F wave,

and normal needle exam

b) Low cmap with normal sensory responses, delayed / absent F

wave, and denervation in at least 2 related musclesc) Low cmap with normal sensory responses, enlarged F wave,

and denervation in at least 2 related muscles


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Components of an EMG

Left Median Motor

O

P

T

R

Wrist

O

P

T

R

Elbow

Left Median Sen Sensory

O

P

T R

2nd Digit

O

P

TR

3rd Digit

OP

T 4th Digit

O

P

T R

1st Digit

EMG - Left CervPara Mid

Nerve conduction studiesMotor nervesSensory nervesRepetitive Stimulation

ElectromyographyQualitativeQuantitative


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Nerve Conduction Studies

Peripheral nerves are stimulated with a controlled

electrical stimulus

Responses are recorded Compound motor action potential (CMAP)

Sensory nerve action potential (SNAP)

F wave

H reflex


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Left Median Motor

O

P

T

R

Wrist

O

P

T

R

Elbow


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Motor NCS Parameters Distal Latency

determined by conduction velocity of the nerve, neuromuscular

junction & muscle

Amplitude

determined by number of muscle fibersactivated

Proximal conduction velocity

determined by conduction velocity of the fastest fibers


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Normal Median Motor Study

DL CV Amp

(msec) (m/s) (mV)

Wrist-APB 3.2 15.0

Elbow-Wrist 55 14.8


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Sensory NCS Parameters

Onset and peak latencies

Conduction velocity

determined by velocity of a very few fast fibers

Amplitude determined by the number of large sensory fibers activated


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Normal Median Sensory Study

1 msec/div

Latency CV Amp

(msec) (m/s) (uV)

Wrist-D2 2.2 58 44.1


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CASE 1

29 y.o. male

Acute right foot drop 4 weeks earlier

No trauma, no hx DM

EXAM: MRC 2/5 rt dorsiflex toes

4/5 rt ankle DF and eversion

Decr pp dorsum foot

Reflexes sym.

No tinel

s at fib head


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Where is lesion

Character (axonal, demyelinating)

prognosis


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.


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CASE 2

67 y.o. male

buttock pain to lat thigh, exac with ambulation

Few wks later rt foot drop

Exam: 4/5 rt foot df, eversion, pf 5-/5

Trace ankle reflexes

Decr sens on dorsum foot

SLR neg


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F-wave study

small late response from a short duration supramaximal stimulation.

It initiates an ant idromicmotorresponse to the spinal cord followedby an or thodromicmotorresponse to the recording electrode.

5% CMAP height

The configuration and latency change with each stimulation.

This is due to a polysynaptic response in the spinal cord, whereRenshaw cells (R) inhibit impulses from traveling the same path each

time.


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F Waves

Useful to assess proximal nerve to spinal cord

Helpful in the evaluation of:

Radiculopathy

Guillian-Barre Syndrome

Peripheral neuropathy

Other demyelinating neuropathies


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F Waves: Normal Median


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H- reflex study late response equivalent to achilles reflex. Stimulate tibial

at popliteal fossa, pickup over soleus muscle

initiated with a submax stimulus at a long duration (0.51.0 ms).

preferentially activates the IA afferent nerve fibers(muscle spindle sensory)

causing an or thodromicsensoryresponse to the spinalcord, and then an or thodromicmotorresponse back tothe recording electrode.

The morphology of wave pattern and latency remainsconstant


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Muscle SpindleIa - responsive to the rate of change in muscle length,

as well to change in velocity
http://en.wikipedia.org/wiki/File:MuscleSpindle.svg


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H Reflexes

Useful to assess proximal nerve conduction

Criteria: 50% diff in

amplitude)

Helpful in the evaluation of: Polyneuropathy

S1 radiculopathy

Upper Motor Neuron lesions


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Nerve Conduction Studies:Late Responses

F Wave Latency Retrograde rebound motor impulse

Travels full length of motor axon and back

Information about proximal segments

Limited sensitivity/specificity

H Reflex Afferent Path: Sensory axons (group Ia fibers)

Efferent Path: Motor Axons (alpha motor neurons)

Follows muscle stretch reflex arc

Side to side latency most valuable


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DDX Small peroneal motor CMAPs normal sensory

No conduction block

Deep peroneal (spares sensory) vs L5

Absent peroneal F points proximal

Normal tibial CMAP + normal sural sensory

Eliminates tibial, sciatic or plexus

Some S1 involvement suggested

H reflex absent with normal M response


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Radiculopathy(Neuro-foraminal Stenosis from L-5 Disc Herniation)


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Radiculopathy(Electrodiagnostic Features)

Normal or low amplitude CMAP in corresponding

dermatome

Normal SNAP in corresponding dermatome Denervation in a segmental myotomal distribution

(at least 2 muscles innervated by the same root

via more than one peripheral nerve) with or

without denervation of paraspinals


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http://www.google.com/url?sa=i&rct=j&q=dorsal%20root%20ganglia&source=images&cd=&cad=rja&docid=QaVeUXsDVfAwBM&tbnid=5LmCVD1eXWYH1M:&ved=0CAUQjRw&url=http://otah2o.wikispaces.com/09+Nervous+System&ei=ID8NUdbjAseH0QHWnYDYBw&bvm=bv.41867550,d.dmQ&psig=AFQjCNFV3yniGkFw633fCeXH2bdUvsA_5Q&ust=1359909020796331


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Needle Electromyography

Needle electrode is inserted into the muscle

Needle is disposable, single use

Multiple muscles are accessible for examination

Combination of muscles tested

Dependent upon clinical question

Level of discomfort is mild


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Needle Electromyography

Muscle is studied at rest and at different levels ofsustained, voluntary contraction.

At rest, the muscle should be silent--any spontaneous

activity may signal a nerve or muscle abnormality.

During activity, the

electrical shape and

pattern of the responsecan distinguish

between nerve and

muscle disease.


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http://www.google.com/url?sa=i&rct=j&q=motor+unit+diagram&source=images&cd=&cad=rja&docid=_3l8DoY7wp_G0M&tbnid=Ia2LpycbobgtqM:&ved=0CAUQjRw&url=http://www.sciencedirect.com/science/article/pii/S1047965107000897&ei=2ZYNUdzIIpKF0QHmjYGgDw&bvm=bv.41867550,d.dmQ&psig=AFQjCNH_MwRz198zFlmDmaNyLSWYCDgxHA&ust=1359931410578948


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EMG - Motor Units

Evaluated during early recruitment

Morphologic parameters studied

Amplitude

Duration Phases

Rule of 5s: as increase effort each unit comes in at ~5hz,

and next added when previous firing ~10hz


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Case 3

53 fem, progressive weak distal L hand No neck pain, numb, loss of bowel, bladder

PHx: dm x 8years, smoker, htn; no sig fhx

Exam: atrophy intrinsics LH

Brisk reflexes UE, and rt babinski present

Normal sens, cerebellar, gait

Init inv: mri c/s mild disk bulging. Emg lt c7-t1 radic.

EMG IS REPEATED AT 7M


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EMG - Denervation Recruitment is the pattern of motor unit firing when a

muscle contracts

Reduced - less motor units to draw upon

Configuration size and shape:

Large Amplitude more that normal # nerve fibers

Large Duration nerve fibers timing is variable


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Needle Electromyography:Neurogenic Motor Unit

EMG - Left VastusLat

This unit demonstrates:

Reduced recruitment

Increased amplitude Increased duration

Polyphasia


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Reinnervation collateral

sprouting


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Needle Electromyography:Muscle at rest

Insertional Activity

Burst of electrical activity as needle is inserted into

muscle

Due to disruption of muscle fiber membranes Prolonged with denervation, some muscle diseases

Spontaneous Activity

Fibrillations, positive sharp waves, fasciculations

Hallmark of denervation, muscle membrane irritation


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Needle Electromyography:Grading of Spontaneous Activity

100 V 10 ms

EMG - Left AntTibialis

0 No Fibs/PSWs

+/- Fibs/PSWs that are not persistent

1+ Persistent Fibs/PSWs in at least 2 areas

2+ Persistent Fibs/PSWs of moderate #s in three or more areas

3+ Persistent Fibs/PSWs of large #s but not obscuring baseline

4+ Baseline obliterated in all areas examined

1+ 2+ 3+ 4+


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Spontaneous Muscle Electrical Activity

Examples:

Fibrillation potential/positive waves

indicates loss of muscle-nerve connection

provides information about the chronicity of the problem

Fasciculation

spontaneous motor unit potential, may indicate irritability in the motor

nerve cell


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Fasciculation


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Case 4

76 healthy female, progressive LE numb / wk 1 year

Imbalance cane walker

Recent involvement of hands

Exam: Motor: grip 4+, hip flex 4, dorsiflex 4-

Sens: marked loss vib and proprioception feet

Areflexic

Gait wide-based; pos Romberg


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Needle 19


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Summary

Sensorimotor polyneuropathy

Cmap loss >> denervation

Conduction blocks

Sig slowing

Few fibrillation potentials, some larger unit ->

predominately chronic


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DDX Chronic acquired demyelinating

neuropathy CIDP +/- early HIV

Multifocal motor NP with conduction block

Anti MAG, monoclonal gammopathy,

MGUS, osteosclerotic myeloma (POEMS syn)

Multiple myeloma, Waldenstroms

Castelmans

Amyloidosis


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Electrodiagnosis provides

Confirmation of neuropathy

Eg vib loss in np vs post cord

Fiber type sens, motor, both

Pathology demyel vs axonal

Chronicity and activity


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Test question

Typical EMG findings in radiculopathy include

a) Low cmap and sensory responses; delayed / absent F wave,

and normal needle exam

b) Low cmap with normal sensory responses, delayed / absent F

wave, and denervation in at least 2 related musclesc) Low cmap with normal sensory responses, enlarged F wave,

and denervation in at least 2 related muscles


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The End


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Limitations of NCSs/EMG

Generally not helpful in the evaluation/diagnosis of:

Pain from joint disease

Fibromyalgia or myofascial pain syndromes

Central nervous system disorders

Disorders that do not arise from the neuromuscular system


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What to Expect From an

EMG Report

A clinically and physiologically relevantinterpretation/diagnosis

An outline of the localization, severity, and acuity of the

process Notation of other diagnoses that are detected/excluded

Explanation of any technical problems


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EMG Report

The reason for the referral is addressed

Pertinent information that may affect management is

provided Need for re-evaluation in the future

Urgent need for medical intervention


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EMG Report

Data obtained during the study: (NCS)

Amplitude

Distal latency

Distance

Conduction velocity

Normal (Reference) data

Side-to-side comparison (when appropriate)

Limb temperature during the study


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EMG Report

Data obtained during the study: (EMG)

Presence & type of abnormal spontaneous activity

Motor unit recruitment

Motor unit morphology


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EMG Pearls

Electrodiagnostic studies are a supplement to, and not areplacement, for the history and physical examination

Electrodiagnostic results are often time-dependent

Electrodiagnostic studies are not standardized

investigations and may be modified by the practitioner toanswer the diagnostic question


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Specialized EDX Testing

Interference pattern analysis

Quantitative motor unit analysis

Single fiber analysis

Segmentation studies

Cranial nerve testing

Brainstem and somatosensory evoked potentials

Pelvic floor and respiratory muscles


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Outline

What conditions are commonly evaluated/diagnosed byNCSs/EMG?

What are the technical details of these studies?

What are some limitations of EMG studies?

What can I expect from an EMG report?

What are the indications for


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What are the indications for

electrodiagnostic

consultation/testing?

Suspected neuromuscular disease

nerve root pathology

peripheral nerve/plexus pathology

neuromuscular junction pathology

muscle pathology


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What is the value of NCSs/EMG?

Confirm the clinical impression of a neuromuscular

disorder

Rule out certain diagnoses

Enhance patient care


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Value of NCSs/EMG

When neuromuscular disease is present,electrodiagnostic testing can:

Clarify the type of pathology (i.e. neuropathy

vs myopathy)

Determine severity & extent of pathology

Confirm site of pathology

Estimate chronicity of pathology

Complaints Suggestive of


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Complaints Suggestive of

Neuromuscular Pathology

Numbness or Tingling

Decreased Sensation

Pain or Cramping

Weakness

Gait difficulty

Fatigue


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Disorders Diagnosed/Evaluated by

NCSs/EMG Generalized Neuropathies

Axonal

DemyelinatingAcquired

Acute: GBS

Chronic: CIDP

Hereditary

Mixed Diabetic sensorimotor neuropathy


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Polyneuropathies

Polyneuropathies associated with many medicalconditions

Multiple investigations often needed

NCSs/EMGs: best initial test to clarify underlying

pathophysiology (i.e., axonal vs demyelination)

Results may help focus rest of work-up


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NCSs/EMG

Mononeuropathy multiplex

Vasculitic/ischemic neuropathies

Demyelinating neuropathies

Infectious neuropathies

Neoplastic infiltration

Granulomatous infiltration Compression neuropathy


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NCSs/EMG Focal Neuropathies

Carpal Tunnel Syndrome (median neuropathy at the wrist)

Ulnar Neuropathy Peroneal Nerve Palsy

Others: brachial plexus lesions, tarsal

tunnel syndrome, etc.


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NCSs/EMG Radiculopathy

Cervical

Lumbar

Motor Neuron Disease

Amyotrophic lateral sclerosis (ALS)

Spinal muscular atrophy (SMA)

Di d Di d/E l t d b


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NCSs/EMG Muscle Disease

Inflammatory

Polymyositis, Dermatomyositis Metabolic

Hereditary or Congenital


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NCSs/EMG

Neuromuscular Junction Disease

Myasthenia Gravis

Lambert Eaton Myasthenic Syndrome

Botulism

Medications

Di d Di d/E l t d b


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NCSs/EMG Generalized weakness in the critical care setting

Acute/unexplained onset of respiratory failure

Neuromuscular cause for failure to wean from

mechanical ventilation

Neuromuscular diseases unique to critical care

setting Critical illness neuropathy/myopathy

Disorders Evaluated/Diagnosed by


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Disorders Evaluated/Diagnosed by

NCSs/EMG

Specialized electrodiagnostic expertise can be useful in

evaluation of:

Ocular muscle weakness

Speech difficulties due to weakness of laryngeal muscles Disorders of movement and tone from central nervous system

disorders


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Neuromuscular Junction Testing

Repetitive Nerve Stimulation

Stimulate nerve with train of supramaximal stimuli before and after

exercise

Record from muscle

Attention to technical factors important

More sensitive recording from proximal muscles

Repetitive Nerve Stimulation:


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3Hz stimulation

Repetitive Nerve Stimulation:Normal


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F-wave study (continued..)


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This is not a reflex, because action potentials travels from the

site of the stimulating electrode in a limb to the spinal cord and

back to the limb in the same nerve that was stimulated. The F- waves latency can be used to derive the conduction

velocity of nerves between the limb and spinal cord, whereas

the motor and sensory nerve conduction study in the same

segment of the limb. Conduction velocity is derived by measuring the limb length in

millimeters from the stimulation site to the corresponding spinal

segment (ex: C7 spinous process to wrist crease for median

nerve).

This is multiplied by 2 as it goes to the cord and returns to the

muscle.

Limitation: This evaluates a long neural pathway, which can

dilute focal lesions and hinder specificity of injury location. It

Radiculopathy


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Radiculopathy(Spontaneous Activity)

EMG - Right LumbPara Mid Fibrillation potentials

Positive sharp waves

Fasciculations

Complex repetitive

discharges

Myokymia (rare)

Myotonia (rare)

Positive Sharp Wave

Complex Repetitive Discharge

Fibrillation Potential

Needle Electromyography:


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Needle Electromyography:Parameters Evaluated

Motor Unit Configuration Muscle is volitionally activated at different force levels

Single motor units are assessed

Single motor unit: A motor axon and all its muscle fibers

Motor Unit Configuration: Amplitude, Duration, Morphology

Motor Unit Recruitment Pattern of motor unit activation with increasing volitional activation

Interference Patterns Motor unit pattern with full voluntary activation



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Needle Electromyography:Parameters Evaluated

Insertional activity

Spontaneous activity

Motor unit configuration

Motor unit recruitment

Interference pattern



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Needle Electromyography:Spontaneous Activity

EMG - Right LumbPara Mid Fibrillation potentials

Positive sharp waves

Fasciculations

Complex repetitive

discharges

Myokymia

Myotonia

Positive Sharp Wave

Complex Repetitive Discharge

Fibrillation Potential


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EMG Review Final Vandersluis