nerve conduction & emg making sense of · 2016. 1. 24. · thoracic outlet syndrome affects the...
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Making sense ofNerve conduction & EMG
Drs R ArunachalamConsultant Clinical Neurophysiologist
Wessex Neurological CentreSouthampton University Hospital
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For the assessment of patients with neuromuscular diseases
Extension of the neurological examination
Directed history and examination followed byNCS and EMG, amended during exam in light of findings
EMG/NCSEMG machine
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Neuromuscular diseasesAnterior Horn cellMotor neurone diseasePolio
RadiculopathyDisc / OsteophytesRoot avulsionTumour / infiltrationInfection
DRGNeuronopathy/ganglionopathy
PlexopathyTraumaNeoplastic / RadiationDiabetic
NeuropathyFocal/entrapmentPolyneuropathy
Sensory / Motor / MixedAxonal / DemyelinatingAcquired / Inherited
Mononeuritis multiplex
Neuromuscular junctionAcquired / congenital
Myasthenia gravisLEMSBotulism
MyopathyCongenitalInflammatoryMetabolicEndocrineMuscular dystrophies
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Sensory nerve study
SNAP = sensory nerve action potential
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CMAP = compound muscle action potential
Motor nerve study
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F - waves
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Goals of NCS / EMG
LocalisationNerve
neuronopathyrootplexusnerve
NMJpre-synapticpost-synaptic
Muscle
CharacterisationPathophysiologyMotor / sensoryFibre sizeAxonal /
DemyelinatingDisease specific
Temporal courseAcuteSubacuteChronic
Severity assessment / Prognosis
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Typical referral questions
● Is this carpal tunnel syndrome / ulnar neuropathy?
● Is this radiculopathy or entrapment neuropathy?
● Is this a brachial plexopathy?
● What is the cause of this patient’s wrist drop?
● Is the nerve lesion improving or recoverable, or is surgery required?
● Does the patient have a peripheral neuropathy?*BPNS 2012
What is normal?●Conduction velocity
Upper limb >50m/s (<38 in demyeln)Lower limb >40m/s
●Distal latencyMedian ≈ 3.5ms (prolonged>4.5)Ulnar ≈ 3.0ms (prolonged>4.0)
●F-latencyUpper limb ≈ 30ms
●Amplitudes Tricky
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Demyelinating vs. Axonal lesion
● DEMYELINATINGloss of / damage to myelinresults in slow conductionoften reversible
● AXONALloss of excitable tissueresults in loss of amplitudeoften irreversible
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Axonal vs. Demyelinating
●Amplitude ↓↓
●Morphology N
●Velocity N/↓
●Distal latency N/↑
●F-latency N/↑
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●Amplitude N/↓Conduction block
●Temporal dispersion
●Velocity ↓/ ↓↓
●Distal latency ↑/↑↑
●F-latency ↑/↑↑
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Slowed conduction – sensory or motor
Reduced amplitudes – sensory or motor
Prolonged distal latencies
F-wave abnormalitiesprolonged minimum F-wave latencyreduced F-wave persistenceabsent F-waveschrono-dispersion of F-wavesmultiple A-waves
Temporal dispersion & Conduction block
Reduced motor unit firing on EMG
Demyelination
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Long distal motor latency
Slowing in intermediate segment
Demyelination
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N-RSwitch: 1Stim:
Non-RecRate: Level: 0.3 msDur: Single 0.0 mA
5 ms Average: Off9.0.0
58.1mA1 mV
100mA
1 mV
1 mV
1 mV
Recording Site: Abductor pollicis brevis
Lat1ms
Durms
AmpmV
AreamVmsStimulus Site
Distmm
Diffms
CVm/sSegment
Recording Site: Abductor pollicis brevis
A1: WristA2: ElbowA2: ElbowA3: AxillaA4: Supraclav fossa
Wrist-ElbowElbow-AxillaAxilla-Supraclav fossa
8.8 6.2 2.0 4.9 16.6 11.1 1.1 5.1
7.8 28 220
A1A1
A2A2A2A2
A3A3
A4A4
5 ms
2-10kHz
1 mV
1 mV
1 mV
1 mV
Sig. Enhancer: Off
2-10kHz
Step: 2
Rec: APB, Stim: Wrist, Elbow, Axil...
Right Median MNCRecord
# 717:04:00
Long distal motor latency
Conduction block ? No – temporal dispersion
Demyelination
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Temporal dispersion
Demyelination
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Conduction block ?
Yes, in the forearm
Yes, at entrapment site
Demyelination
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Needle EMG
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FASCICULATIONS
● New Folder\VP_20080123_19-22-51.exe● New Folder\VP_20080122_19-00-21.exe
● Spontaneous discharge of an entire motor unit
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FIBRILLATIONS
● New Folder\VP_20080122_19-06-44.exe
● Spontaneous discharge of a single muscle fibre
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RECRUITMENT
● New Folder\VP_20080122_19-10-01.exe● New Folder\VP_20080122_19-04-18.exe
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CRD, Polyphasia
● New Folder\VP_20080122_19-12-13.exe
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Carpal tunnel
syndrome
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Typical findings in CTS
●Initial changes are mainly sensory●‘Bifid’ response from ring finger●Median slower than ulnar●↓amplitude
●Motor changes occur later●↑distal motor latency●↓amplitude in severe cases
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Ulnar neuropathy at elbow
●Sensory findings●↓ digit V amplitude ●↓ ulnar dorsal cutaneous amplitude●↓ CAP (mixed nerve response)
●Motor findings●Slowing across the elbow●Conduction block across the elbow (drop in
amplitude)
●EMG changes in hand & forearm muscles
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Ulnar neuropathy at wrist
●Sensory findings●↓ digit V amplitude ●Normal ulnar dorsal cutaneous amplitude●Normal CAP (mixed nerve response)
●Motor findings●↑ distal motor latency●Normal conduction – forearm and elbow
●EMG changes confined to the hand
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Brachial plexus
●Sensory changes↓ amplitude - “postganglionic”Often no significant change
●Motor nerve conductionCan be normalReduction in amplitude - severe casesF-wave abnormalities
●Diagnosis based on EMG abnormalitiesKnowledge of brachial plexus anatomy helps
localisethe lesion
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Thoracic outlet syndrome
●Affects the lower trunk / medial cord
●Sensory changesIn ulnar territoryOften medial antebrachial nerve is involved
●Motor changesOften in median nerve territory
●EMG abnormalitiesC8/T1 innervated muscles (median>ulnar)
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Cervical radiculopathy
●Sensory nerve conductionNormal despite significant symptoms“Preganglionic lesion”
●Motor nerve conductionMostly normalOccasionally F-wave abnormalitiesReduction in amplitude - rare, severe cases
●Diagnosis based on EMG abnormalitiesKnowledge of myotomes help localise the levelNormal EMG does not exclude root disease
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Peripheral neuropathy
●Often ‘length dependent’Feet affected firstUsually symmetrical
●Sensory nerve conductionReduced amplitudesReduced velocities
●Motor nerve conductionReduced amplitudesReduced velocitiesF-wave abnormalities
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CASE STUDIES
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Tingling fingers - ?Carpal tunnel syndrome
● CTS● high median● brachial plexus● C6 radiculopathy
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Wasted hand ? Cause
Muscle diseaseUlnar nerveLower brachial PlexusC8/T1 rootAnterior horn cell
Sensory – 15µV
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