In addition, the calculation of F-wave velocities and F ratios permits comparison of conduction in the proximal versus the distal nerve segments. 15, 38, 40, 67, 71, 102, 111, 120, 128, 162 In a diffuse process, F-wave latencies, reflecting accumulated conduction delay, often clearly exceed the normal range even in patients with a borderline conduction abnormality. Explored first in patients with Charcot-Marie-Tooth disease (CMT) 61 and motoneuron diseases, 106 the method has since gained popularity in evaluation of a variety of neurologic conditions as part of routine nerve conduction studies. Nonetheless, F wave usefully supplements the conventional nerve conduction studies (NCS) in characterizing neuropathic disorders in general and polyneuropathies in particular. The inherent variability of the latency and waveform makes its use technically more demanding than that of the compound muscle action potential (CMAP), or muscle (M) response. It, thus, helps assess motor conduction along the entire length of the peripheral axons, including the most proximal segment.
The F wave results from backfiring of antidromically activated anterior horn cells.
