EMG Spontaneous Abnormalities

EMG Spontaneous Abnormalities

EMG spontaneous abnormalities

Positive sharp waves
Fasciculation potentials
Complex repetitive discharges
Myokymic potentials

Originate from spontaneous firing of single muscle fiber
Detectable 2-3 weeks after “denervation”
Initial positive deflection, negative spike
consistent with axonal degeneration
may be seen in acute myopathy
sound like rain on tin roof or fat frying in a pan
Positive sharp waves

Originate from spontaneous firing of single muscle fiber
May appear earlier than fibs
Initial positive deflection without negative spike
Sound like ticking of clock
Fasciculation potential

Spontaneous discharge of all or part of a motor unit
Muscle fasciculation visible clinically as “twitching” or worm like movements
Appear similar to volitional MUP; must make sure muscle at rest
May be benign or pathologic
Complex Repetitive discharges

Result of ephaptic activation of neighboring muscle fibers
One muscle fiber acts as generator
Non specific abnormality; hyper-irritable muscle membrane
Sound like motor boat or motor cycle
Abruptly start or stop
Myokymic Potentials

Represent rhythmic firing of “grouped” MUPs
“grouped fasciculations”
sound like footsteps of marching soldiers
always pathologic
common in radiation induced brachial plexopathy
Myotonic discharge

“dive bomber” sound
waxing and waning of amplitude, frequency
induced by tapping muscle or moving needle
represent “delayed relaxation” of muscle fibers
seen in Myotonic dystrophy, myotonia congenita


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Ray Jurewicz
E-mail: rj@NerveStudy.com

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