F-responses in syringomyelia

Motor and sensory nerve conduction and various F-response parameters have been examined in the median and ulnar nerves bilaterally in 22 patients with syringomyelia. Excluding those nerves with isolated peripheral lesions, motor and sensory conduction was normal in the distal nerve segments, except for one subject in whom severe wasting of the muscles was associated with slowed motor velocities. Minimum and/or maximum F-response latencies were increased in one or more nerves in 16 of the 22 cases, which was attributed to disturbed function of anterior horn cells and the intraspinal segment of the motor fibres, or mild subclinical nerve trauma. There was a tendency for F-response amplitude and duration to be increased, probably reflecting the combined effects of spasticity and enlargement of motor units due to reinnervation.