Discography is a well-established diagnostic tool for degenerative disc disease (DDD) [1]. Through discography, degenerative disc changes can be observed by dye injection, and provocation tests are sometimes used as a reference for the diagnosis of DDD. In addition, before surgery for the disc that causes a patient’s lower back pain, discography is performed to confirm the level before surgery, and the postoperative course is better [2].

Buttermann [3] utilized discography for therapeutic purposes in addition to its diagnostic use for DDD and reported that the intradiscal steroid injection (ISI) during discography improved low back pain in patients with DDD [4]. Pain relief following ISI is attributed to the suppression of inflammatory mediators in the disc; steroid seeps out through the annular tear and spreads to the neural elements on the periphery of the disc and posterior longitudinal ligament [3,5,6].

Considering the therapeutic efficacy of ISI in DDD, whether ISI is effective not only for discogenic back pain but also for neurogenic intermittent claudication in patients with spinal stenosis is investigated, where DDD acts as an important pathology. Most lumbar spinal stenosis cases are thought to result from a cascade of age-related changes initiated by disc degeneration [7,8]. As regards nonsurgical treatment, some studies have evaluated the effectiveness of epidural steroid injection (ESI) for patients with spinal stenosis. Given the widespread use of ESI as a treatment modality for patients with spinal stenosis, the authors hypothesized that the steroid introduced through ISI permeates regions with disc degeneration and diffuses throughout the epidural space, thereby alleviating both discogenic back pain and leg pain. Therefore, this study aimed to analyze the contribution of ISI to symptom improvement in patients with spinal stenosis and explore whether ISI can be a viable alternative in reducing the need for surgical intervention in such patients.

Of the 401 patients who underwent ISI for lumbar spinal stenosis at our center between January 2013 and December 2019, 141 were excluded from the analysis (118 did not undergo more than 1 year of follow-up at the outpatient clinic, and 23 underwent multilevel ISI). Finally, 260 patients were included. The mean±standard deviation age of the patients was 62.7±14.1 years. ISI was most frequently conducted at L4/5 (n=201), followed by L5/S1 (n=25), L3/4 (n=24), and L2/3 (n=10). Magnetic resonance imaging conducted before ISI revealed Modic changes around the disc in 39 patients; type 1, 2, and 3 changes were observed in six, 27, and six patients, respectively. Furthermore, within the Pfirrmann grading system, 28, 208, and 24 patients had grades 3, 4, and 5, respectively. A total of 29 patients (11.2%) experienced provocation of discogenic back pain during dye injection similar or identical to their usual symptoms. The basic demographics of the patients are shown in Table 1. After ISI, the initial leg pain VAS (8.91) showed a significant improvement compared with the initial measurement, with scores of 4.42 (p<0.001) at week 2 and 4.70 (p<0.001) at week 6 after the procedure. Similarly, the initial back pain VAS (8.85) also exhibited a significant improvement compared with the initial measurement, with scores of 4.58 (p<0.001) at week 2 and 4.79 (p<0.001) at week 6 after the procedure (Table 1). Furthermore, the group with unilateral leg pain before the procedure showed a more significant improvement in leg VAS scores following the procedure compared with the group with radiating pain on both sides (Table 2).

Despite the majority of patients having initial back and leg VAS scores in the average range of 8, conservative treatment alone proved to be effective for up to 1 year after the ISI without the need for surgical intervention (n=228, 87.7%). A total of 32 patients (12.3%) experienced persistent and worsening neurogenic claudication and underwent surgery such as posterior lumbar interbody fusion or laminectomy within 1 year after the procedure. No significant differences were found in the overall demographics between the surgical and nonsurgical groups, respectively. However, at week 6 after the ISI, the back pain VAS score was significantly higher in the surgical group (6.22) than in the nonsurgical group (4.57, p=0.019). Similarly, the leg pain VAS was significantly higher in the surgical group (5.75) than in the nonsurgical group (4.55, p=0.017) (Table 3). Furthermore, the patients who underwent surgery showed a notable trend of worsening back pain and leg pain VAS scores at week 6 despite having shown improvement at week 2. In contrast, the nonsurgical group maintained the improvement in both back and leg pain until week 6 (Table 4).

Several studies have reported the use of ISI for the treatment of low back pain in patients with DDD [3,4,11]. Buttermann [3] evaluated the effectiveness of ISI and ESI in patients who exhibited DDD symptoms for >1 year. Both spinal steroid injections were beneficial for a small number of patients with advanced DDD and chronic low back pain. Among patients who received an ISI, those with inflammatory end-plate changes (Modic change) had more favorable outcomes than those without inflammation. Nevertheless, most studies to date have performed ISI in patients with DDD. To our knowledge, no studies have investigated the use of ISI in patients with spinal stenosis. This research highlights the clinical value of ISI in delaying surgical intervention for up to a year in patients with spinal stenosis. The findings indicate that ISI is beneficial in alleviating back and leg pain in patients with spinal stenosis.

The pathogenesis of spinal stenosis is multifactorial, and vascular factors (e.g., venous engorgement and arterial insufficiency) can lead to ischemic neuritis [8,12–15]. Many inflammatory mediators have been implicated in the radicular symptoms of spinal stenosis [16]. Indeed, the symptoms of spinal stenosis may be attributed to inflammation-related nerve compression. Steroids provide pain relief by reducing local inflammation in the stenosis area [17]. Following injection into the degenerated disc, steroids flowed to the annular tear area and spread to the anterior aspect of the dura within the spinal canal. Consequently, when the stenotic lesion is located in the central zone, lateral recess, or foraminal zone of the spinal canal, the medication is believed to flow more directly to the degenerated areas, thereby enhancing the anti-inflammatory effect. In selective root blocks, the needle is typically positioned posterior to the root rather than anterior to it, with the medication focusing on the exiting root rather than the pathology within the spinal canal [8]. However, in ISI, the medication is injected directly into the disc, allowing it to flow toward the degenerated areas, causing dura compression. This is presumed to achieve a broader anti-inflammatory effect, affecting not only the exiting root but also the traversing root. In addition, compared with root blocks, the wider diffusion of medications with ISI is thought to relieve both radiating and back pains by simultaneously blocking the medial branch nerves that serve the facets and nerves surrounding the disc. Furthermore, patients with unilateral lower extremity pain reported greater satisfaction with treatment outcomes than patients with pain in both lower extremities. We speculate that steroids seeping out from the torn annulus fibrous may relieve inflammation more effectively around the nerve root on the symptomatic side. This suggests that, during ISI, the medication may have been delivered more effectively to the area of root compression in patients with spinal stenosis accompanied by disc extrusion. Therefore, spinal stenosis with unilateral leg pain may be a good indication for ISI.

Considering the high pain relief effect after ISI in patients with spinal stenosis, ISI could serve as a diagnostic tool for spinal stenosis. In this study, discography was performed in patients with a Pfirrmann grade of ≥2, as confirmed by magnetic resonance imaging. However, during dye injection, pain occurs only in 11.2% of the patients. Considering that >90% of the patients reported pain improvements 2 weeks after ISI, the provocation of pain via dye injection does not appear to be significantly relevant for diagnosing patients with spinal stenosis than ISI. This may result from a combination of factors, including disc degeneration, ligamentum flavum, and facet hypertrophy, which contribute to the symptoms of spinal stenosis. Based on the results of this study, the ISI could be used as an effective diagnostic tool, as well as a therapeutic tool, for spinal stenosis.

In this study, no instances of subdural injection occurred following ISI, and no cases had epidural hematoma or infection after the procedure. Because ISI involves injecting medications into the disc, it is inherently safe from risks such as headaches caused by dural puncture or seizures resulting from subdural injection [18]. This can be considered a clear advantage of ISI over ESI. However, directly injecting medications into the disc through a needle puncture may accelerate disc degeneration [19,20]. There is some reassurance on this point, as Kim et al. [21] suggested that ISI did not accelerate the histological degeneration of the disc. In their study, 150 patients who underwent PLIF for L4–5 spinal stenosis were analyzed. They compared groups who had received ISI before surgery with those who had not and conducted histological analysis of the annulus pulposus tissue obtained during discectomy. The results indicated that ISI did not induce further degeneration in chondrocyte proliferation or granular matrix changes. However, this assessment of histological degeneration was limited to chondrocyte proliferation and granular matrix changes in the annulus pulposus. Therefore, the evidence is insufficient to conclusively state that ISI does not cause degeneration. Future studies with molecular-level analyses are needed to provide a more comprehensive evaluation.

This study has some limitations. First, because ISI was not compared with other conservative treatment types, additional studies are required to provide a direct comparative analysis. However, studies of patients with lumbar spinal stenosis have reported that 15%–45% of the patients experience improvements in symptoms following nonoperative therapy, whereas 15%–30% experience a worsening of symptoms [22–26]. Considering that approximately 87.7% of the patients who underwent ISI in this study could perform their daily activities without the need for surgery for approximately 1 year after the procedure, ISI can be regarded as a promising alternative in the treatment of patients with spinal stenosis. In future studies, a prospective comparison is essential to evaluate the effectiveness of various treatment modalities, including neuroplasty and ESI, which are currently widely performed [27]. Second, the lack of uniformity in conservative treatment methods (e.g., medication types and dosages) among patients following the ISI may have influenced the decision-making process for follow-up therapeutic approaches. Third, the utility of ISI was assessed solely based on pain severity measured by the leg and back VAS, which serves as a clinical evaluation tool for the patients. In cases of spinal stenosis, where claudication is the primary symptom, improvements in ambulation before and after the procedure must be comprehensively evaluated. Furthermore, incorporating assessments that comprehensively evaluate the effect on daily living activities, such as the Oswestry disability index or the 36-Item Short Form Survey, would provide a more thorough analysis of treatment outcomes [28,29]. Nevertheless, the significance of this research lies in its pioneering evaluation of clinical outcomes in patients with spinal stenosis following ISI based on their initial pain levels. Finally, ISI was primarily performed on patients with a Pfirrmann grade of ≥2 and high initial back pain VAS scores. However, further studies are needed to determine whether ISI could be an effective therapeutic alternative for patients with spinal stenosis experiencing with minimal disc degeneration and low initial back pain VAS scores. This occurs because, in cases with little to no disc degeneration, the medication injected into the disc may have difficulty spreading effectively into the spinal canal.

ISI is a useful nonsurgical alternative for patients with single-level lumbar spinal stenosis accompanied by unilateral leg pain. Moreover, when a significant pain relief effect is observed up to 6 weeks after the ISI, the need for surgery within 1 year due to the corresponding pathologic lesion tends to decrease significantly. This finding signifies the proposal of a new nonsurgical treatment option for patients with spinal stenosis.