Concordant pressure paresthesia during interlaminar lumbar epidural steroid injections correlates with pain relief in patients with unilateral radicular pain.

BACKGROUND Transforaminal and interlaminar epidural steroid injections are commonly used interventional pain management procedures in the treatment of radicular low back pain. Even though several studies have shown that transforaminal injections provide enhanced short-term outcomes in patients with radicular and low back pain, they have also been associated with a higher incidence of unintentional intravascular injection and often dire consequences than have interlaminar injections. OBJECTIVES We compared 2 different approaches, midline and lateral parasagittal, of lumbar interlaminar epidural steroid injection (LESI) in patients with unilateral lumbosacral radiculopathic pain. We also tested the role of concordant pressure paresthesia occurring during LESI as a prognostic factor in determining the efficacy of LESI. STUDY DESIGN Prospective, randomized, blinded study. SETTING Pain management center, part of a teaching-community hospital in a major metropolitan US city. METHODS After Institutional Review Board approval, 106 patients undergoing LESI for radicular low back pain were randomly assigned to one of 2 groups (53 patients each) based on approach: midline interlaminar (MIL) and lateral parasagittal interlaminar (PIL). Patients were asked to grade any pressure paresthesia as occurring ipsilaterally or contralaterally to their "usual and customary pain," or in a distribution atypical of their daily pain. Other variables such as: the Oswestry Disability Index questionnaire, pain scores at rest and during movement, use of pain medications, etc. were recorded 20 minutes before the procedure, and on days 1, 7, 14, 21, 28, 60, 120, 180 and 365 after the injection. RESULTS Results of this study showed statistically and clinically significant pain relief in patients undergoing LESI by both the MIL and PIL approaches. Patients receiving LESI using the lateral parasagittal approach had statistically and clinically longer pain relief then patients receiving LESI via a midline approach. They also had slightly better quality of life scores and improvement in everyday functionality; they also used less pain medications than patients receiving LESI using a midline approach. Furthermore, patients in the PIL group described significantly higher rates of concordant moderate-to-severe pressure paresthesia in the distributions of their "usual and customary pain" compared to the MIL group. In addition, patients who had concordant pressure paresthesia and no discordant pressure paresthesia (i.e., "opposite side or atypical") during interventional treatment had better and longer pain relief after LESI. Two patients from each group required discectomy surgery in the one-year observation period. LIMITATIONS The major limitation of this study is that we did not include a transforaminal epidural steroid injection group, since that is one of the approaches still commonly used in contemporary pain practices for the treatment of low back pain with unilateral radicular pain. CONCLUSIONS This study showed that the lateral parasagittal interlaminar approach was more effective than the midline interlaminar approach in targeting low back pain with unilateral radicular pain secondary to degenerative lumbar disc disease. It also showed that pressure paresthesia occurring ipsilaterally during an LESI correlates with pain relief and may therefore be used as a prognostic factor.