A sensitive electrodiagnostic method for detecting sensory conduction deficits in an experimental single lumbar...

For a single L5 radicular lesion produced by constant, localized compression, sequential changes of epidurally recorded potentials after sciatic nerve stimulation or direct L5 root stimulation were compared with those after indirect L5 root stimulation with a collision technique in rats.

To determine whether the use of the collision technique improves the diagnostic yield of the lumbosacral-evoked potential study for a single radicular lesion.

Clinical recording of the evoked potentials at serial intervertebral spaces after stimulation of the peroneal or the tibial nerve was less sensitive than what might be expected for a single radicular lesion, presumably because peripheral nerve stimulation activates more than a nerve root, thereby normal responses arising from the unaffected roots tending to mask mild conduction abnormalities of the diseased root. Furthermore, direct stimulation of the nerve root with a monopolar electrode, despite potential advantages, produces an overloading stimulus artifact. This precludes accurate recording because of the short distance between the stimulus and recording sites. A collision technique should circumvent these problems.

A vascular clip was applied to the L5 root and evoked potentials were recorded epidurally at T10-11 after sciatic nerve stimulation (Group 1, 11 rats), L5 root stimulation (Group 2, 14 rats), or a combination of L6 root and sciatic nerve stimulation (Group 3, 11 rats), at 3-minute intervals during a 15-minute period of compression and additionally 15 minutes after release of the compression.

The N1 potential significantly decreased in amplitude immediately after L5 root compression and then decreased slightly but progressively in all three groups. Throughout the recording, the N1 peak amplitude, shown as a percentage relative to the baseline value, was significantly smaller in Groups 2 and 3 than in Group 1, whereas there was no significant difference between Groups 2 and 3. The removal of the compression caused a significant recovery of the N1 peak amplitude in Groups 2 and 3, but not in Group 1.

The present animal experiment demonstrated that the collision technique improved the sensitivity of the lumbosacral-evoked potential for a single radicular lesion. With this technique, the evoked potential study in the clinical domain will identify conduction abnormalities more consistently than peripheral nerve stimulation alone.