Repeater F-waves: Clinical Importance and Distinction from A-waves

Abstract

Aim: The aim of this study was to distinguish repeater F-waves (Frep) from A-waves by measuring the amplitude and ratio and investigating their relationship with neuromuscular diseases (NMDs). Materials and Methods: We retrospectively reviewed and compared the Frep records of 414 patients with different NMDs and 162 control subjects with normal electrophysiologic findings. Optimal cutoff points were determined using receiver operating characteristic curves, yielding >99% specificity versus A-waves. Results: The sensitivity at each derived cutoff point for the median, ulnar, peroneal, and tibial nerves were 58.5% for ≥340 uV, 46.2% for ≥350 μV, 13.1% for ≥560 μV, and 50.1% for ≥410 μV, respectively. However, the Frep/M-response amplitude ratio demonstrated very low sensitivity. The occurrence of repeater F-waves (Freps) was similar in patients with primary demyelination and axonal degeneration (P > 0.05); however, it was higher than that in control subjects (P < 0.017). The Frep amplitudes in patients with primary demyelination were significantly lower than in patients with axonal degeneration and control subjects (P < 0.017). The M-response amplitude negatively correlated with the occurrence of Freps and positively correlated with the F-wave persistence (P < 0.001). Discussion: The amplitude parameter appears to be an essential criterion for assessing late potentials, which may help differentiate Freps from A-waves, thereby facilitating the accurate detection of Freps. The increased occurrence of Freps indicates dysfunction of lower motor neurons, independent of the pathophysiologic process.

Keywords

• a-wave
• frep amplitude
• f-wave
• late responses
• repeater f-wave