1-A-D-13. Repeater F-waves may be derived from the reinnervated type I motor unit in polio survivors

Despite our previous report that repeater F-waves are characteristic findings in polio survivors, the origin of these repeater F-waves remains to be clarified. In this study, 43 polio survivors (polio group) and 20 healthy age- and height-matched volunteers (control group) underwent motor conduction studies of their bilateral median and tibial nerves, including F-waves elicited by 100 stimuli. The polio group showed significantly prolonged F-wave minimal latency in the median nerve compared to the controls. The mean F-wave amplitude was not significantly different between the groups. Concerning the repeater F-waves in the polio group, minimal latencies were significantly prolonged, and their mean amplitudes were significantly higher than for the non-repeater F-waves of both nerves. According to publications on muscle pathology, polio survivors show a characteristic predominance of type I muscle fibers. Therefore, these repeater F-waves, with a prolonged minimal latency and high amplitude, might be derived from the reinnervated type I motor unit. These findings suggest that repeater F-waves could indicate motor unit pathophysiology in polio survivors.