NCS-F WAVES

SUMMARY

1. F waves are a late response received from a round trip from the stimulus site, to the spinal motor neuron & back to the muscle. Normal: 32ms in the UL and 55ms in the LL.

2. F waves are heterogeneous, derived from different populations of motor neurons for each response.

3. Because of this variability, one must sample multiple F waves (typically 10 to 20).

4. Parameters measured: minimal latency (the shortest latency of multiple responses), mean latency (the average latency), maximal latency (the longest latency of multiple responses), chrono-dispersion (difference between the shortest and longest latencies), persistence/penetrance is measured as the percentage of stimulations that produce an F wave.

5. Absence of F waves is considered abnormal.

6. Rate of false-positive results is cumulative, hence only minimal/mean latency & absence of F-wave is useful.

7. Useful in evaluation of radiculopathy, GBS, demyelinating & peripheral neuropathies.

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].