CNP Course - EMG Waveforms Flashcards
origin of EMG potentials
single muscle fibers
EMG potentials that fire alone
end plate spikes
fibrillation potentials
myotonic discharges
EMG potentials that fire in groups
adjacent muscle fibers -
- complex repetitive discharge
- insertion activity
EMG potentials - spontaneous
fasciculation potentials
myokymic discharges
neurotonic discharges
regular firing pattern with linear change is:
fibrillation potential
regular firing pattern with no change is:
complex repetitive discharge
regular firing pattern with exponential change is:
myotonic
irregular firing pattern is:
random change
end plate spike
semi rhythmic firing pattern is
motor unit potential
increased insertional activity
early denervation
normal variants (snap, crackle, pop)
decreased insertional activity
fatty or fibrotic tissue
severe atrophy
periodic paralysis
ischemic muscles
technical
grading fibrillation potentials
reflects number of denervated fibers:
1+ persistent single trains
2+ moderate numbers
3+ many in all areas
4+ completely fill baseline
associated disorders of fibrillation potentials - neurogenic
anterior horn cell disorders -e.g. ALS
radiculopathies - “active”
mononeuropathies - “severe”
axonal peripheral neuropathies
associated disorders of fibrillation potentials - myopathic
inflammatory (e.g. polymyositis, IBM)
toxic myopathies (e.g. statin, hydroxychloroquine)
muscular dystrophies
metabolic (e.g. acid maltase)
fiber necrosis, fiber splitting, vacuolar damage
associated disorders of fibrillation potentials - severe NMJ disorders
myasthenia gravis (severe)
LEMS
botulism
single motor unit
all the muscle fibers innervated by one AHC
factors affecting MUP morphology
technical: electrode type, filter settings
physiologic: muscle, subject’s age, temperature
rise time
time from peak positive deflection to peak negative deflection
represents proximity to muscle fiber action potential
should be <0.5msec
amplitude
sum of action potentials of muscle fibers closest to recording electrode
usually less than 15 muscle fibers (1-8)
determined by diameter of muscle fibers, number of muscle fibers, and temporal distribution of potentials closest to electrode
duration
time from leaving baseline until return
- synchrony of firing, fiber density, area of motor unit, intervening tissue, proximity to recording electrode, age and muscle
most limb muscles: 8-12msec
temporal course of MUP changes in acute neurogenic injury:
normal
1 minute: reduced recruitment
1-2 months: unstable, turns
2-6 months: polyphasic, long duration
>6 months: long duration
myotonic discharges
regular, exponential change, wax/wane
stock plane
associated disorders myotonic discharges - prominent
myotonic dystrophy (DM1 and DM2)
myotonia congenita
paramyotonia congenita
hyperkalemic periodic paralysis
associated disorders myotonic discharges - occasional/infrequent
polymyositis
acid maltase deficiency (esp paraspinals)
drug-induced myotonia
- cholesterol lower agents, colchicine
associated disorders myotonic discharges - rare
neurogenic disorders (e.g. axonal neuropathies, radiculopathies)
complex repetitive discharges
regular, fixed intervals (abrupt onset, cessation, change)
rate 3-40Hz
configuration: few-multiple spikes, stable or unstable
jackhammer
associated disorders complex repetitive discharges - neurogenic
anterior horn cells - e.g. ALS, SMA
radiculopathies - chronic, old
axonal peripheral neuropathies - longstanding
associated disorders complex repetitive discharges - myopathic
inflammatory - e.g. IBM
muscular dystrophies
associated disorders complex repetitive discharges - normal
iliopsoas
biceps
fasciculation potentials
firing pattern: single, random, irregular, 1-100 per minute
form: no standard configuration, often distant
irregular pattern
popcorn
associated disorders fasciculation potentials - neurogenic
anterior horn cell disorders - e.g. ALS, SMA
radiculopathies
axonal peripheral neuropathies
associated disorders fasciculation potentials - other
hyperexciteable nerve syndromes (cramp-fasciculation syndrome)
tetany
hyperthyroidism
anti-cholinesterase medication (e.g. mestinon)
fasciculation potentials normal in
benign fasciculations
myokymic discharges
1 or few MUP firing repetitively in bursts
burst pattern: regular or semirhythmic
marching
associated disorders myokymic discharges - extremities
radiation
chronic nerve compression (CTS)
AIDP, CIDP
gold therapy
rattlesnake venom
associated disorders myokymic discharges - most likely
radiation nerve injury
associated disorders myokymic discharges - facial
multiple sclerosis
sarcoid, tuberculoma
brainstem glioma
polyradiculopathy
meningeal carcinomatosis
facial palsy
syringobulba
ALS
neuromyotonic discharges
regular (wane), very high frequency
racecar
associated disorders neuromyotonic discharges
syndrome of continuous muscle fiber activity (Isaac’s)
tetany
anticholinesterase poisoning
chronic spinal muscular atrophies
recruitment ratio
maximum firing rate/# of nearby MUP
most limb muscles have ratio of </= 5 (15Hz: 3 MUP, 20Hz: 4 MUP)
reduced recruitment
increase in firing rate without increase in MUPs
disorders with reduced recruitment
hallmark of neurogenic process
correlates with weakness
disorders with reduced recruitment - neurogenic
axon loss (e.g. mononeuropathies, radiculopathies, neuropathies)
loss of anterior horn cells (e.g. ALS)
conduction block (e.g. Saturday night palsy)
disorders with reduced recruitment - myopathies
severe myopathy with loss of all muscle fibers in some motor units (e.g. end-stage muscular dystrophy)
recruitment grading
fastest rate of firing of 1st MUP when 2nd MUP recruited and/or recruitment ratio
1+ (mild) rate of 1st >10Hz, ratio >5
2+ (moderate) rate of 1st >15Hz, ratio >7.5
3+ (severe) rate of 1st >20Hz, ratio >10
poor activation
effort
pain
central disorder: stroke, myelopathy
disorders of unstable (varying) motor unit potentials - neurogenic
ongoing reinnervation after axonal loss - e.g. ALS, recovering radiculopathy
disorders of unstable (varying) motor unit potentials - NMJ disorders
myasthenia gravis
LEMS
disorders of unstable (varying) motor unit potentials - myopathies
reinnervating muscle fibers
phases and turns
asynchronous firing
phase = baseline crossings +1
polyphasic MUP = 5 or more phases
when do you see polyphasic MUPs
myopathies
MUP changes in myopathies
reduced motor unit territory
- reduction of # of muscle fibers/motor unit
- reduction in muscle fiber size
decreased duration of MUP
decreased amplitude of MUP
increased phases of MUP (desynchrony)
disorders with short duration MUPs - neurogenic
early reinnervation from severe nerve damage (nascent MUP)
disorders with short duration MUPs - myopathic
inflammatory - e.g. polymyositis, IBM
muscular dystrophies
myotonic dystrophy
congenital myopathies
toxic myopathies (not corticosteroids)
disorders with short duration MUPs - NMJ disorders
myasthenia gravis
LEMS
botulism
MUP changes in neurogenic disorders
loss of axons -> reduced number of MUP, reduced recruitment
collateral sprouting -> loss of synchrony of fibers, change in appearance
