Conduction velocity in the forearm segment of the median nerve in patients with impaired conduction through the carpal tunnel.

Conduction velocity, in the forearm segment of the median nerve, has been investigated in a group of patients with carpal tunnel syndrome. Motor conduction velocity was reduced below 50 m/s in 18% of the sample. Although a correlation between severity of compression and forearm motor conduction velocity was demonstrated, it was weak (r = 0.51) and slow forearm velocities occurred in some patients who had only a minor abnormality at the carpal tunnel itself. In patients with uncomplicated carpal tunnel syndrome, slow motor conduction in the forearm segment of the median nerve was accompanied by only a small reduction (approx. 5 m/s) in mixed nerve conduction velocity. By contrast, in patients whose abnormality at the carpal tunnel was accompanied by evidence of a more widespread sensorimotor neuropathy, mixed nerve conduction velocity was reduced in parallel with the change in motor conduction velocity.