NCS-EMG (NORMAL ACTIVITY)

SUMMARY

1. Needle EMG assesses nerve and muscle function.

2. A recording needle electrode is placed into a muscle to evaluate: insertional activity, resting activity, voluntary recruitment, exertional activity.

PARAMETERS

3. Insertional activity (normal 300ms):brief electrical discharge from muscle when inserting a needle electrode into it.

- Prolonged/increased activity (300-500ms) can be seen in in both neuropathic & myopathic conditions.

- Reduced insertional activity (< 300ms) is seen in muscle ischemia (due to vascular occlusion or compartment syndrome), necrosis fibrosis & if it is not muscle.

4. Normal spontaneous (resting) activity: After a needle is inserted into a normal muscle, there should be electrical silence at rest. However, if it is placed into or near the NMJ (motor endplate), two waveforms can occur: Miniature End Plate Potentials (MEPP) & End Plate Potentials (EPP).

5. Voluntary recruitment: refers to the ability to add successive motor units to increase the force of a contraction.

6. Exertional activity (motor unit action potential, MUAP): compound action potential from muscle fibers belonging to a single motor unit, within the recording range of the needle electrode.

Reference(s)

Wilkinson, I., Furmedge, D. and Sinharay, R. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press. Get it on Amazon.
Feather, A., Randall, D. and Waterhouse, M. (2020). Kumar And Clark’s Clinical Medicine. 10th ed. S.L.: Elsevier Health Sciences. Get it on Amazon.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].