Sensory nerve somatosensory evoked potentials as add-on diagnostic procedure to imaging procedures in patients with sciatica.

The aim of the present study was to evaluate the ability of sensory nerve somatosensory evoked potentials (SEP) to discriminate between lumbar spine computed tomography (CT) findings with and without relevance for the radiating sensory symptoms in patients with sciatica in whom myelography does not have such discriminatory capacity. Forty consecutive sciatic patients in whom CT without intrathecal contrast showed degenerative changes which did not cause probable compression in at least one symptomatic nerve root, or caused probable compression in at least one asymptomatic nerve root, and in whom there were corresponding discrepancies between the radiating sensory symptoms and myelographic nerve root compression, were studied. Sensory nerve SEP representing nerve roots L4, L5 and S1, were performed in all patients. The sensory nerve conduction velocity (SNCV) and the amplitude of the sensory nerve action potential (SNAP) were recorded from the stimulated nerves. The odds ratios (OR 95% CI) of the association of positive SEP to symptomatic nerve roots were 24.0 (4.8 to 54.5) in nerve roots with probable and 39.0 (5.9 to 258.9) with possible CT compression. The corresponding associations between myelography and sciatic symptoms were not statistically significant. Comparisons of SNCVs and SNAP amplitudes did not indicate that postganglionic nerve dysfunction contributed to the sensory symptoms or to the SEP results. SEP examination may be used to discriminate between CT findings with and without relevance to the radiating sensory symptoms in patients with sciatica in whom myelography does not show this discriminatory capacity.