NCS-MOTOR TESTING PARAMETERS

SUMMARY

Tip: amplitude is decreased in axonal neuropathies; CV & latency are prolonged in demyelination

1. Distal motor latency: time from stimulation to onset of muscle contraction. Determined by the conduction velocity of the nerve, NMJ & muscle

- Prolonged in demyelination, compression

2. Amplitude: represents the size (number of axons participating) of the response, measured from baseline to peak or from peak to peak, depending upon how the reference data were collected
- Varies with stimulus intensity, impedance, skin temperature
- Reduced with axonal neuropathies, conduction block in demyelination
- Elevated in early denervation due to polyphasic potentials

3. Conduction velocity (CV): distance between the stimulation and recording electrodes divided by the onset latency
- Prolonged in demyelination

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].