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long duration MUAPs are seen when?
early stages of deymelination
the discharge of APs is prolonged, so summation takes longer than usual.
also seen in myopathy, but in that case there's also decreased amplitude
long duration polyphasic MUs are seen when?
describe what's going on
indicates a neuropathy if > 10% of the MUs in a muscle are polyphasic
- electrical conduction to each fiber in the MU is prolonged
- some terminal end fibers of the axon lost their ability to conduct an AP and activate a muscle fiber
- lower number of muscle fibers contributing to the MUAP, so now the e characteristics of each stage are more distorted
- --> multiple stages with prolonged duration
appearance: multiple peaks, then a short group of squiggles
large amplitude MUs - indicate what
healing process after a chronic partial nerve injury
the high amplitude is a result of collateral sprouting that is now innervating extra muscle fibers
disease affecting stability of muscle membrane
leads to eventual muscle fiber necrosis
Periph nerves are basically intact, so conduction of motor axons is WNL, tho in later stages may have changes in terminal branches of motor axons
progression of myopathy results in
- loss of viable muscle fibers
- loss of strenght
- changes in terminal branches of motor axons
EMG changes in myopathy
- short duration a/o low amplitude of MUAP
- (can look like fibs, but start/stop under vol control)
early complete interference pattern
EMG is good to rule in/out myopathy
short duration MUs happen why?
loss of muscle fibers in MU
The majority of the fibers contributing to overall duration of summated MUAP died off, so the MU looks electrically shorter in duration than normal.
short duration MUs occur secondary to what?
Low amplitude MU due to what?
decrease in muscle fibers that contribute to peak summation MUAP
long duration, long duration polyphasic, a/o large amplitude