The effect of epidural steroid injection on the natural history of lumbar disc herniation

Abstract

Glenn R. Buttermann, MD, Stillwater, MN, USAIntroduction: The natural history of lumbar herniated nucleus pulposus (HNP) is that most decrease in size. Prior computed tomography and magnetic resonance imaging (MRI) studies have found that most HNPs resorb with time on serial scans. Furthermore, patients' symptoms typically improve as a disc herniation regresses. The effect of epidural steroid injection (ESI) in treating pain resulting from HNP has been studied by numerous authors, and a recent meta-analysis suggests that ESIs are effective in a small proportion of patients. A recent study by the author evaluated 169 patients with symptomatic HNP in which the size was greater than 25% of the spinal canal. During the study period, 69 patients improved without invasive treatment during the first 6 weeks after the onset of their symptoms. Another 100 patients, whose symptoms did not improve, were randomized to treatment: of these, 50 patients underwent discectomy and another 50 patients underwent lumbar ESI. For the ESI group, 23 patients (46%) had a successful result; the rest then had discectomy. Follow-up MRI scans were obtained in patients who had a successful ESI as well as in those 69 patients who improved without invasive treatment at an average of 18 months after the onset of their symptoms. This forms the basis of this study with the purpose of determining whether ESI-treated patients improve because of steroid effect and/or resorption of the HNP.Methods: Patients who underwent successful ESI for lumbar HNP had follow-up MRI scans in 20 of 23 cases. In the patients who had spontaneous improvement in symptoms, follow-up MRI scans were randomly obtained in 37 of 69 patients. Follow-up MRI scans were compared with the initial MRIs obtained at the onset of symptoms. Axial MRI images of the involved disc as well as adjacent normal levels were scanned and digitized on a personal computer. The area encompassed by the disc herniation within the spinal canal was determined for all patients on the initial and follow-up scans.Results: The average area of the initial disc herniation for the ESI-treated patients was 42%±8% of the spinal canal. The average area of the HNP on follow-up MRI scan was 15±10% of the spinal canal. The average decrease in size was 27%. Five HNP (25%) resorbed entirely (less than 10% of initial size), 12 HNP were smaller in area and 3 (15%) were unchanged. In the ESI group, two of three patients who did not have a decrease in the size of the HNP were improved on their outcomes survey. In the group who had improvement without invasive treatment, the initial size of the HNP was 42%±10%. On follow-up MRI, the size of was 17%±11%, an average decrease of 25%. Seventeen patients (46%) had resorption of their HNP, 16 patients had a decrease in size of their HNP and 4 (11%) were unchanged. Of the four without regression of their HNP, two of them improved substantially and two only minimally. For this group, sequestered and extruded disc herniations were the most likely to resorb. In the ESI group, 11 patients (55%) had sequestered and/or extruded disc herniations of which three resorbed entirely. In the spontaneously improving group, 21 patients (57%) had sequestered and/or extruded disc herniations of which 14 resorbed entirely. Outcome surveys at 1 year (visual analog scale, pain drawing, Oswestry disability scale) were similarly improved for both groups.A similar decrease in HNP size was found whether or not a patient received lumbar ESI at 1- to 2-year follow-up.Discussion: In patients treated nonoperatively for lumbar disc herniation, we could not find a significant effect of ESI on the size or extent of HNP resorbtion. Epidural steroid injection was effective in many patients in decreasing symptoms, but in terms of actually altering the natural history of HNP morphology, we could not detect a significant difference in the two groups. Epidural steroids may be useful in treating pain during the period required for the natural history of disc herniation to decrease or resorb.