F52. Repeater F-waves: Electrophysiologic manifestations of upper or lower motor neuron involvement?

Introduction The aim of this study is to compare repeater F-wave parameters with CMAP amplitudes recorded from the hand muscles (as indicators of the amount of lower motor neuron [LMN] loss) and with the triple stimulation technique (TST) ratios in the same muscles (as indicators of upper motor neuron [UMN] involvement) in 19 patients with amyotrophic lateral sclerosis (ALS). Methods Ninety F-waves were recorded from thenar and hypothenar muscles by supramaximal stimuli applied to the relevant nerves at the wrist level. Repeater F-waves (F rep ) were visually defined as those presented with the same amplitude, latency and shapes. Repeater neuron (RN) index, F rep index, persistances of F-waves, F/M amplitude ratio and the neurophysiologic index (NI) were calculated. By depending our laboratory normals, TST ratio values lower than 82% and 86% were accepted as abnormal showing UMN involvement in thenar and hypothenar muscles respectively. Results TST ratios were abnormal in 13 thenar and 11 hypothenar muscles. None of the F rep parameters showed any significant relationship with the abnormal TST ratios, except the lower F rep index in thenar muscles, in patients with UMN involvement according to low TST ratios. However, there was a strong negative correlation with the CMAP amplitudes and F rep index and RN index values in hypothenar muscle (Spearman’s rho, p Conclusion These findings imply that repeater F waves might be a manifestation of LMN loss more than being a result of UMN involvement.