Ch 5 - EDX: EMG Flashcards by Chris Garrison

What does needle EMG assess?

Nerve and muscle function:

Insertional activity
Resting activity
Voluntary recruitment

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What does insertional activity represent?

Discharge potentials mech evoked by disrupting muscle cell mem w/ needle

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When is increased insertional activity seen?

Neuropathic and myopathic conditions

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When is decreased insertional activity seen?

Muscle atrophy

Muscle ischemia d/t vascular occlusion or compartment synd

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What is normal duration of insertional activity?

300 ms

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What waveforms can be produced with needle placement near NMJ?

MEEP and EPP

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What are miniature end plate potentials (MEPP)?

Normal spontaneous exocytosis of individual quanta of Ach traveling across NMJ

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Describe the morphology, amp, duration and rate of miniature end plate potentials (MEPP)?

Negative monophasic
Amp 10-50 uV
Duration 0.5-1.0 ms
Rate 150 Hz

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What are end plate potentials (EPP)?

Endplate spikes d/t release of ACh provoked by needle irritation of muscle fiber or sync of several MEPPs

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What are end plate potentials (EPP) the result of?

Propagated single muscle fiber AP

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What is the hallmark sign of end plate potentials (EPP)?

Irregularity and negative deflection

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Describe the morphology, amp, duration and rate of of end plate potentials (EPP)?

Neg biphasic morphology
Amp <1000uV (mV)
Duration 2.0-4.0ms
Rate 50-100Hz

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Describe the sound of end plate potentials (EPP)?

Sputtering fat in a frying pan

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Describe the sound of miniature end plate potentials (MEPP)?

Sea shell murmur

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Where are ABN spontaneous activity generated from?

Muscle fiber
motor unit (neural source)

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What is a fibrillation potential (FIB)?

Spon firing AP origninating from denervated single muscle fibers 2/2 uncontrolled ACh release

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What the hallmark sign of a fibrillation potential (FIB)?

Regularity of firing

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What is a positive sharp wave (PSW)?

Needle recording of an AP of a single muscle fiber

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What inhibits the display of neg deflection of the waveform of a PSW?

Propagation to but not past needle tip

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Describe the initial deflection, duration and amp of a FIB.

Initial deflection: Positive (biphasic)
Duration: 1-5 ms
Early Amp: >300 uV
Late Amp: <25 uV

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Describe the initial deflection, duration and amp of a PSW.

Initial deflection: Positive (biphasic)
Duration: 10-30 ms
Amp: <1 mV

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Describe the sound of a FIB.

Rain on a tin roof

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Describe the sound of a PSW.

Dull thud or chug

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What are Complex repetitive discharges (CRDs)?

Polyphasic/serrated AP originating from a principal pacemaker, initiating a group of single muscle fibers to fire near synchrony

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How is current spread in CRDs?

Ephaptic transmission

What is the hallmark sign for CRDs?

Regular interval b/w each discharge and within each discharge

Describe the sound of CRDs

Motor boat

What are myotonic discharges?

Biphasic single muscle fiber AP triggered by needle movement, percussion or voluntary contraction

What causes myotonic discharges?

Alteration of ion channels in muscle membrane

What is the hallmark sign of myotonic discharges?

Smooth change in rate and amplitude

What medication can cause myotonic discharges?

Propanolol

Describe the sound of myotonic discharges

Dive bomber

What are Fasciculations?

Spon discharges originating from any portion of a single motor unit and result in intermittent muscle fiber contraction

When are Fasciculations considered pathological?

If associated with FIB or PSWs

What is the hallmark sign of Fasciculations?

Irregular firing motor unit

What are Myokymic discharges?

Groups of MUAPs firing repetitively

Describe clinical myokymia

Slow continuous muscle fiber contractions. Rippling appearance of overlying skin.

What is the hallmark of Myokymia?

Semiregularity b/w each discharge and w/in each discharge

Describe the sound of Myokymia

Marching soldiers

What are etiologies of facial Myokymia?

MS Brainstem neoplasm Polyradiculopathy Bell's palsy

What are etiologies of extremity Myokymia?

Radiation plexopathy Compression neuropathy Rattlesnake venom

What are Neuromyotonic discharges?

Discharges originating from motor axons

What are Neuromyotonic discharges classically seen in?

Neuromytonia (Isaac's syndrome)

What is Neuromytonia (Isaac's syndrome)?

Disorder w/ continuous muscle fiber activity resulting in muscle rippling and stiffness secondary to irritable nerves

What is the progressive decrement of waveform in Neuromytonic discharge due to?

Individual muscle fiber fatigue and drop off

Describe the sound of Neuromyotonic discharges.

Tornado-like

What are Cramp discharges?

Involuntary repetitive firing of MUAP's in a large area of muscle

What are artifact potentials?

Waveforms that obscure neurophysiologic signals

What is exertional activity?

Voluntary muscle fiber activity electrically recorded as a MUAP

What is a Motor Unity Action Potential (MUAP)?

Compound action potential from muscle fibers belonging to a single motor unit

How is MUAP amplitude measured?

Most positive to most negative peak

How can MUAP amplitude be increased or decreased?

Inc: reinnervation process Dec: loss of muscle fibers Variable: NMJ d/o

What is a normal MUAP amplitude?

1 mV

What is the Rise time of a MUAP?

Time it takes a MUAP to go from baseline to peak of negative wave

What a normal Rise time of a MUAP?

<500 us

What does the duration of a MUAP represent?

of muscle fibers w/in a motor unit

How is the duration of a MUAP measured?

Waveforms inital departure from baseline to its final return

How can the duration of a MUAP change?

Inc: motor unit territory inc from collateral sprouting Dec: loss of muscle fibers

What is the normal duration of a MUAP?

5-15 ms

What are turns or serrations of MUAP?

Changes in direction of the waveform that do not cross the baseline

What do phases of MUAP represent?

Synch of muscle fiber AP firing

How are phases of MUAP calculated?

of baseline crossings +1

What is considered polyphasicity of MUAP?

5 or > crossings

What causes Long duration, large amplitude polyphasic potentials (LDLA)?

Denervation and reinnervation from collateral sprouting | referred to as neuropathic potentials

What causes short duration, small amplitude polyphasic potentials (SDSA)?

Drop out or dysfunction of muscle fibers | referred to as myopathic potentials

What disorders are short duration, small amplitude polyphasic potentials (SDSA) seen in?

Myopathic diseases NMJ disorders Severe neuropathic injury l/t nascent motor unit potentials

What are unstable potentials?

Variation of MUAP's amp, duration and slope.

What disorders are unstable potentials MC seen in?

NMJ d/o which cause irregular blocking of discharges

What are satellite potentials?

Small potentials seen in early reinnervation

What is a Doublet/multiple potentials?

2 or > MUAPs firing recurrently and together in semi-rhythmic fashion

What disorders are Doublet/multiple potentials seen in?

``` Ischemia Hyperventilation Tetany Motor neuron d/o Metabolic dz ```

What are Giant potentials?

Extremely large MUAPs (> 5 mV)

What disorder are Giant potentials seen in?

Poliomyelitis

What is Recruitment?

Ability to add successive motor units to inc the force of contraction

What is the rule of 5's in normal MUAP recruitment?

Onset freq of first MUAP begins at 5 Hz When firing of 1st MUAP reaches 10 Hz, a 2nd MUAP starts at 5Hz When 1st MUAP at rate of 15 Hz, 2nd should be at 10Hz and 3rd at 5 Hz

What is Early recruitment?

ABN early firing of many MUAPs with mild contraction

What conditions are Early recruitment seen in?

Myopathic conditions that result in loss of muscle fibers and some NMJ d/o

What is Reduced recruitment?

Firing of only a few MUAPs with even maximal contraction

What conditions are Reduced recruitment seen in?

Neuropathic conditions | Severe myopathies

What is the Firing rate (FR) of recruitment?

of times a MUAP fires/second expressed in Hz

What is the recruitment frequency (RF)?

Firing rate of 1st MUAP when the 2nd MUAP begins to fire

What is the normal recruitment frequency (RF)?

<20 Hz | >20 Hz: neuropathic process

What is the recruitment interval (RI)?

Interspike interval (in ms) b/w two discharges of the same MUAP when a 2nd MUAP begins to fire

What is the normal recruitment interval (RI)?

~100 ms

Describe the recruitment interval and frequency in neuropathy.

Dec interval | Inc frequency

Describe the recruitment interval and frequency in myopathy.

Inc interval | Dec frequency

Etiology of FIBs and PSWs

Nerve: anterior horn cell dz, radiculopathy, plexopathy, peripheral neuropathy, mononeuropathy NMJ: Myasthenia gravis, botulism Muscle: Muscular dystrophy, polymyositis, dermatomyositis, hyperkalemic periodic paralysis, acid maltase deficiency

Etiology of Complex Repetitive Discharges (CRDs).

Nerve: anterior horn cell dz, chronic radiculopathy, peripheral neuropathy, Muscle: Muscular dystrophy, polymyositis, dermatomyositis, limb-girdle dystrophy, myxedema Normal variant

Etiology of Myotonic discharges.

Nerve: chronic radiculopathy, peripheral neuropathy Muscle: Muscular dystrophy, myotonia congenita, paramyotonia, polymyositis, dermatomyositis, hyperkalemic periodic paralysis, acid maltase deficiency

Etiology of Fasciculations

Nerve: Anterior horn cell disease, tetany, Creutzfeldt-Jakob syndrome, radiculopathy, mononeuropathy Metabolic: Thyrotoxicosis, tetany Normal variant

Etiology of neuromyotonic discharges

Nerve: Anterior horn cell disease, tetany Toxins: Anticholinesterase

Etiology of cramp discharges

``` Salt depletion Uremia Pregnancy Myxedema Polonged muscle contraction Myotonia congenita Myotonic dystrophy Stiff-man’s syndrome ```

Etiology of artifact potentials

``` EMG instrument Printer Unshielded power cords Electrical outlets Fluorescent lights Pacemaker ```

How is Recruitment ratio calculated?

Dividing FR of the 1st MUAP by # of different MUAPs on the screen

What is a normal Recruitment ratio?

<10

What is the interference pattern?

Qualitative or quantitative description of the sequential appearance of MUAPs

What is the interference pattern composed of?

Recruitment plus activation

What is Activation?

Ability of a motor unit to fire faster to produce a greater contractile force

How can activation be decreased?

CNS diseases Pain Hysteria

What is a complete pattern?

No individual MUAPs can be seen. A full screen represents four to five MUAPs

What is a reduced pattern?

Some MUAPs are identified on the screen during a full contraction

What is a discrete pattern?

Each MUAP can be identified on the screen during a full contraction

What is a single unit pattern?

One MUAP is identified on the screen during a full contraction