Electrical stimulation of the epiradicular space using a catheter with a removable stylet

ABSTRACT

BACKGROUND: Electrical stimulation can be used to verify the location of epidural catheters. Although epiradicular localization of a catheter is important for patients with radiating pain in the lower extremities due to spinal stenosis or disc herniation, no prospective study results pertaining to the stimulation threshold within the epiradicular space have been reported. Therefore, we set out to investigate the threshold current for motor response in the epiradicular space by the use of a catheter containing a removable stylet. In addition, this study examines the reliability of such epiradicular stimulation. METHODS: In 105 patients undergoing a retrograde interlaminar ventral epidural injection, a lumbar epiradicular catheter was inserted. Loss of resistance was used to identify the epidural space. Afterward, the TheraCath was advanced into the epiradicular space and connected to a nerve stimulator. A nerve stimulator delivered progressively, increasing electrical current until an appropriate muscle contraction was observed. Contrast media was then injected and epiradicular dispersal was assessed. RESULTS: Epiradicular stimulation yielded a mean threshold of 0.56 +/- 0.50 mA (range 0.06 to 2.84). When compared with epiradicular dispersal as a gold standard, the sensitivity, specificity, positive predictive value, and negative predictive value of epiradicular stimulation with the TheraCath were 90%, 56%, 96% and 33%, respectively. CONCLUSIONS: The threshold current of an insulated needle required to elicit a motor response in the epiradicular space was evaluated. We conclude that the epiradicular stimulation test is useful for confirming catheter placement. Nonetheless, further studies are required before implementing its routine use in clinical settings.