Needle EMG
PERFORMING THE NEEDLE ELECTROMYOGRAPHIC EXAMINATION
* Five steps in the needle examination
(1) the muscle at rest
(2) insertional activity
(3) minimal to moderate isometric muscle contraction
(4) information synthesis
(5) impression formulation
1) Muscle at Rest
; monopolar needle
- reference electrode is located relatively close to the site of insertion and
a ground is placed on the patient in a convenient location
; standard concentric needle
- only requires a separate ground as the cannula is the reference electrode.
2) Insertional Activity
0.5-2 mm increments with a several-second pause between each insertion
pyramidal region
- Insertional activity ( "injury potential" )
3) Minimal To Moderate Contraction/Recruitment
- generated by the voluntary activation of motor units
- instructed to gently activate by just "thinking" of a small contraction
- electrical potentials produced by all of the single muscle fibers innervated by one nerve
summate to form a motor unit action potential (MUAP) with characteristics that can be
assessed, such as morphology and recruitment
- performance of routine qualitative needle electromyography
; gross abnormalities of MUAPs
1) amplitudes approaching 5 mV or more (Giant MUAPs)
2) MUAPs with more than four phases (polyphasic MUAPs)
3) MUAP durations abnormally long or short
4) recruitment disturbances
- moderate to maximal contraction
: evaluate interference pattern
4) Information synthesis
with the history and physical examination
5) Impression formulation
electrodiagnostic medicine impression