Ch 5 - EDX: EMG Flashcards
What does needle EMG assess?
Nerve and muscle function:
- Insertional activity
- Resting activity
- Voluntary recruitment
What does insertional activity represent?
Discharge potentials mech evoked by disrupting muscle cell mem w/ needle
When is increased insertional activity seen?
Neuropathic and myopathic conditions
When is decreased insertional activity seen?
Muscle atrophy
Muscle ischemia d/t vascular occlusion or compartment synd
What is normal duration of insertional activity?
300 ms
What waveforms can be produced with needle placement near NMJ?
MEEP and EPP
What are miniature end plate potentials (MEPP)?
Normal spontaneous exocytosis of individual quanta of Ach traveling across NMJ
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
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
What are end plate potentials (EPP) the result of?
Propagated single muscle fiber AP
What is the hallmark sign of end plate potentials (EPP)?
Irregularity and negative deflection
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
Describe the sound of end plate potentials (EPP)?
Sputtering fat in a frying pan
Describe the sound of miniature end plate potentials (MEPP)?
Sea shell murmur
Where are ABN spontaneous activity generated from?
Muscle fiber motor unit (neural source)
What is a fibrillation potential (FIB)?
Spon firing AP origninating from denervated single muscle fibers 2/2 uncontrolled ACh release
What the hallmark sign of a fibrillation potential (FIB)?
Regularity of firing
What is a positive sharp wave (PSW)?
Needle recording of an AP of a single muscle fiber
What inhibits the display of neg deflection of the waveform of a PSW?
Propagation to but not past needle tip
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
Describe the initial deflection, duration and amp of a PSW.
Initial deflection: Positive (biphasic)
Duration: 10-30 ms
Amp: <1 mV
Describe the sound of a FIB.
Rain on a tin roof
Describe the sound of a PSW.
Dull thud or chug
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
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
