nerve conduction & emg making sense of · 2016. 1. 24. · thoracic outlet syndrome affects the...

Making sense ofNerve conduction & EMG

Drs R ArunachalamConsultant Clinical Neurophysiologist

Wessex Neurological CentreSouthampton University Hospital

*BPNS 2012

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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