Our results show that the use of F-waves may improve the electrodiagnosis of the ULSR if the number of repeater waves is evaluated given the clear and consistent increase of this variable in patients with lumbosacral root injury.

Intramuscular Stem Cells in ALS justify exploring the efficacy of this procedure in further patients and other muscles, through Phase II trials.Clinical Trial Registration www.clinicaltrials.gov (identifier NCT02286011); EudraCT number 2011-004801-25.

The absence or a prolonged latency of late responses, like F‐waves, is a common neurophysiological finding with diagnostic utility in the early Guillain‐Barré syndrome. However, the presence and the number of repeater F‐waves have not been studied in this disease. In four patients, we report the transient presence of repeater F‐waves in nerves of the lower limbs shortly after the onset of the disease. In each patient, the initial (diagnostic) nerve conduction study showed a high incidence of repeater F‐waves in the tibial or in the peroneal nerves of one side, with normal distal motor latencies; in the other nerves explored the F‐waves were fully abolished and the motor potentials were abnormal. In a second study, done 2–6 weeks later, we observed the abolition of the F‐waves or a significant increase of its minimal latency in those nerves in which we had detected the repeaters. The presence of a high number of repeater F‐waves with normal latencies in some nerves may be a transient and initial electrophysiological sign useful in the early diagnosis of this disease.