Clinical value of F-wave recordings in traumatic cervical spinal cord injury.

F-waves and motor/sensory nerve conduction (NCS) of the median and ulnar nerves were examined in 66 patients with traumatic motoneurone lesion due to acute and chronic cervical spinal cord injury (SCI). The examinations were performed in parallel in chronic tetraplegics once and in acute tetraplegic patients monthly for the first 3 months, after 6 months and 1 year post-trauma. A pathological reduction of the compound muscle action potential (CMAP) (in 10% even a complete loss of the CMAP) was present in about 50% of the patients. The mean CMAP values of tetraplegic patients with either acute or chronic SCI were significantly (P < 0.001) reduced compared to normal subjects. Because sensory nerve conduction in these patients was normal, the reduction of CMAP should be due to damage of intramedullar motoneurones or anterior nerve roots. While in all chronic SCI patients with preserved CMAP F-waves could be elicited, 50% of the acute SCI patients showed a complete loss of F-waves of both nerves during the initial examination due to spinal shock. After 6 months all acute SCI patients with preserved motor potentials regained F-waves. Therefore, the excitability of F-waves is influenced by spinal shock in acute SCI. The mean F-wave latencies (Fmin-response, Fmin-M response) revealed no significant difference between healthy subjects and SCI patients. However, the frequency of F-wave production was related to the severity of the motoneurone lesion. Furthermore, while the F-wave latencies and CMAP values did not change significantly with time after acute SCI, the frequency of F-wave production increased, but remained reduced compared to normal subjects.