Latency of late responses in lesions of lumbosacral nerve roots.

Latencies of the F response and the H reflex discharge have been measured in 16 patients with clinical signs of lesions affecting the lumbosacral nerve roots. Responses were recorded from relevant muscles with stimulation of the posterior tibial or lateral popliteal nerves. In seven of the 12 patients with electrophysiological abnormalities, one or more late responses were absent. Radiographic examination in the same group confirmed disc lesions at L4-L5 or L5-S1 levels in nine patients and at T12-L1 in one and showed diffuse degenerative spine disease in two. Three of the four patients with normal electrophysiological results had mild lumbosacral disc disease. It is concluded that measurement of late response latencies is a useful investigation in lumbosacral nerve root disease.