Presence of repeater F-waves in the early stage of Guillain-Barré syndrome.

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.