Evaluation of Lumbosacral Nerve Root Lesions Using Evoked Potentials Recorded by a Surface Electrode Technique

Abstract

Patients with lumbar disc herniation were studied with lumbosacral evoked potentials (EPs). To evaluate lumbosacral EPs for the functional diagnosis of nerve root lesions in patients with lumbar disc herniation. No clinical studies have been conducted using lumbosacral EPs elicited by body surface leads. Lumbosacral EPs elicited by stimulating the posterior tibial nerve were recorded using surface electrodes placed over the interspinous processes of T12-S1. By subtracting the waveform recorded at NT12 (T12/L1 potential) from that at NL3 (L3/L4 potential), NL3' (residual potential) potentials were clearly identified. NT12 and NL3' potentials were classified into four groups based on the degree of the reduction of amplitude and/or the prolongation of latency. Significant correlations were found between the NL3' score and the straight-leg raising test score (r = 0.36, P < 0.05) and between the NT12 amplitude and sensory disturbance (r = 0.37, P < 0.02). The NL3' score was 1.2 +/- 0.5 points before surgery, and it significantly improved to 2.5 +/- 0.5 points 2 months after surgery (P < 0.05). Short-term, the NT12 amplitude did not change significantly. Twelve months after surgery, the NT12 amplitude improved significantly to 1.1 +/- 0.5 microV (P < 0.05). The results of this study indicated that the NL3' score may reflect impairment of the impulse traversing the nerve root in the acute clinical stage, whereas the NT12 amplitude reflects a neurologic deficit. The postoperative clinical course can be estimated by observing recovery of the NL3' score and NT12 amplitude.