Epidural recording of nerve conduction studies and surgical findings in radiculopathy

We developed a method of studying nerve conduction along proximal nerves and nerve roots by delivering supramaximal stimuli to the tibial and peroneal nerves within the popliteal space and recording compound nerve action potentials from an epidural needle electrode at the L4-L5 interspace. For the purpose of investigating lumbar radiculopathies, a battery of averaged potentials was developed that could be read side-to-side for symmetry of amplitude and latency. Decreased amplitude and/or increased latency in peroneal or tibial conduction studies was attributed to L5 or S1 root pathology respectively. We report on 22 patients who were studied with this method and subsequently went to surgery. To evaluate the ability of the procedure to predict surgical findings, we reviewed the last 155 patients that we studied using epidural recording to find those who had subsequently gone to surgery and were sufficiently documented to allow analysis. The review yielded 22 cases and 69 root levels whose condition had been reported at surgery and studied by our method. Agreement was above what might be expected by chance p < .0001 (7.462; sign). The agreement on nerve root condition between nerve conduction studies and surgical findings suggests that the procedure's usefulness for confirming and localizing pathology in nerve root entrapments is similar to that offered by nerve conduction studies for entrapment neuropathies elsewhere.