NCS-EMG (MUAP ABNORMALITIES)

SUMMARY

1. Spontaneous activity: fibrillations & positive sharp waves seen in denervation & inflammatory myopathy.

2. Long duration, large amplitude polyphasic potentials (LDLA): typically occur as a result of denervation and reinnervation from collateral sprouting. This reinnervation process causes an increased number of muscle fibers per motor unit.
- Causes: inflammatory or dystrophic myopathy.

3. Neuropathic potentials: reduced/discreet recruitment, high amplitude, long duration, polyphasic potentials that occur from a denervation and reinnervation process.

4. Myopathic potentials: increased/early recruitment, low amplitude, short duration, polyphasic potentials that occur from muscle disorders.

5. Unstable potentials (NMJ disease): increased/early recruitment, motor unit instability (MUAP will vary in size & morphology) due to irregular blocking of discharges.

6. Giant potentials: refers to the extremely large MUAPs (> 5mV) that occur in poliomyelitis.

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].