The outcomes of intra-articular corticosteroid injection into sacroiliac joint following findings of single-photon emission computed tomography imaging: a retrospective case series

Dear Editor: The sacroiliac joint (SIJ) is the pain generator in 10%–30% of patients presenting with chronic low back pain.1 SIJ pain is usually felt in the buttock and can radiate to the lower back, groin, and posterior thigh.2 Treatment options include oral medication, physical therapy, and corticosteroid injections (CSI) into the SIJ.3 Corticosteroids have a strong anti-inflammatory effect, and patients with evident inflammation within or around the SIJ should have a better therapeutic outcome to CSI than those without. Anatomic imaging modalities, including radiography, computed tomography, and magnetic resonance imaging, can identify sites where degenerative changes and other anatomical abnormalities occur, but they have limitations in localizing the exact pain generators.4 In contrast, bone single-photon emission computed tomography (SPECT) allows the accurate localization of metabolically active sites.4 Bone tracers preferentially localize in areas of bone remodeling and increased perfusion, which could identify sites of inflammation and pain in the SIJ.5 Also, bone SPECT was shown to accurately determine the location of therapeutic injection for controlling low back pain.6,7 Accordingly, bone SPECT imaging could be useful in predicting the therapeutic outcome of intra-articular CSI in patients with SIJ pain by assessing the presence of inflammation within or around the SIJ. Here we evaluated the treatment outcome of intra-articular CSI in patients with SIJ pain based on increased radiotracer uptake on bone SPECT imaging. This study was conducted retrospectively in a single university hospital. Consecutive patients with ipsilateral or bilateral buttock pain who visited the rehabilitation department between March 2009 and December 2012 were recruited. The inclusion criteria were: 1) age between 20 and 80 years; 2) SIJ pain diagnosed on the basis of physical examination (≥3/6 positive provocation tests, including distraction test, compression test, thigh thrust test, Gaenslen test, sacral thrust test, and the FABER test) and diagnostic intra-articular injection of 1 mL of 2% lidocaine (≥50% temporary pain relief) under the fluoroscopy, SIJ pain was diagnosed; 3) patients who underwent bone SPECT prior to intra-articular CSI; 4) SIJ pain sustained for at least 3 months prior to intra-articular CSI; 5) pain ≥ 4 on the numeric rating scale (NRS, 0 = no pain and 10 = worst pain imaginable) prior to injection; and 6) follow-up performed 1 month after the injection. Patients with SIJ infections or spondyloarthritis were excluded.8 Patients were placed in prone position and the C-arm (Siemens) was oriented to optimize SIJ visualization. Under sterile conditions, a 25-gauge, 3.5-inch needle was inserted into the SIJ, confirmed by arthrogram with contrast material. Then, a mixture of 0.5 mL of 2% lidocaine, 20 mg triamcinolone acetonide, and 1 mL of normal saline was injected. The included patients received 740 MBq of technetium-99m methylene diphosphonate (Tc-99m MDP) and underwent SPECT imaging approximately 3 hours after the administration of the radiotracer. A nuclear medicine physician specialist with over 15 years of experience evaluated the bone SPECT findings (Figure 1). The finding of bone single-photon emission computed tomography imaging in a 30-year-old female with sacroiliac joint (SIJ) pain. An increased radiotracer uptake was found in the left SIJ. As for all the SPECT imaging studies, the images were acquired using a two-headed SPECT system (Hawkeye; GE healthcare, Milwaukee, WI, USA) under the following imaging conditions: low-energy high-resolution collimation, energy window peak at 140 KeV (20% windowing of 126–154 KeV), scatter window at 120 KeV (10% windowing of 115–125 KeV), step and shoot mode at 3° intervals over 180°, and a 30 s dwell time per stop. SPECT images were reconstructed using an iterative ordered subset expectation maximization (OSEM) algorithm with 2 iterations and 10 subsets into a 64 × 64 matrix. No scatter or attenuation correction was applied. Pain intensity levels were assessed using an NRS before intra-articular CSI and 1 month after treatment. Successful treatment was defined as ≥ 50% reduction in the NRS score. Data were analyzed using the Statistical Package for Social Sciences (SPSS) version 26.0 (IBM Corp., Armonk, NY, USA). We compared the data of two groups, SPECT+ group (SIJs showing increased radiotracer uptake on bone SPECT) and SPECT– group (SIJs with no increased radiotracer uptake). Demographic data, NRS scores, and ratios of successful treatment were compared using the Mann–Whitney U test and χ2 test. Intragroup differences between the initial and 1 month follow-up NRS were compared using the Wilcoxon signed-rank test. P < 0.05 was set as statistically significant. The charts of 66 patients who received intra-articular SIJ CSI were reviewed. After excluding 40 patients (30: no bone SPECT, 5: < 3 months of pain onset, 2: < 4 NRS score of initial pain, 3: no 1-month follow-up data), 26 patients were recruited and 37 SIJs were diagnosed as painful. Of the 37 SIJs, 20 SIJs from 14 patients showed increased radiotracer uptake on bone SPECT (SPECT+ group) and 17 SIJs from 12 patients did not show increased uptake (SPECT- group). Comparing the demographic data, the SPECT+ group was significantly younger than the SPECT− group (Mann–Whitney U test, P < .001) (Table 1). Data other than age, including initial NRS scores, were not significantly different. In the intragroup comparison, NRS scores at 1-month follow-up were significantly reduced in both groups (Wilcoxon signed rank test, SPECT+ group: P < .001, SPECT− group: P = .003). The change in NRS scores was more significant in the SPECT+ group than in the SPECT − group (Mann–Whitney U test, P = .036). In the SPECT+ group, 75% (95% confidence interval = 5.75–8.65) of patients reported >50% pain relief compared to only 29.4% in the SPECT− group. The ratio of successful treatment was significantly higher in the SPECT+ group than in the SPECT− group (χ2 test, P = .009) (Table 1). The demographic data, NRS scores, and ratios of successful treatment of SPECT+ and SPECT- groups NRS = numeric rating scale; SIJ = sacroiliac joint; SPECT = single-photon emission computed tomography. P values in bold indicate P < .05. The demographic data, NRS scores, and ratios of successful treatment of SPECT+ and SPECT- groups NRS = numeric rating scale; SIJ = sacroiliac joint; SPECT = single-photon emission computed tomography. P values in bold indicate P < .05. Pain reduction after CSI in SIJs showing increased radiotracer uptake on bone SPECT imaging was significantly greater than in SIJs without increased uptake on bone SPECT. Successful treatment (≥ 50% pain reduction) rate was significantly higher in the SPECT+ group. Several studies have reported that bone SPECT can be useful to identify joints, mostly facet joints, and a few cases of SIJ, causing pain.6,7,9,10 However, they did not evaluate the therapeutic outcome of SIJ CSI according to bone SPECT findings. Nonetheless, this retrospective study has several limitations: 1) a small number of patients were included; 2) follow-up occurred at 1 month after CSI; 3) SPECT was conducted without setting criteria in advance; and 4) this study was conducted retrospectively. In conclusion, therapeutic outcomes of intra-articular CSI on SIJ pain were more favorable in cases showing increased radiotracer uptake on bone SPECT than in SIJs showing no increased uptake. We believe that bone SPECT can be useful to predict the clinical response to CSI in SIJ pain patients. Prospective studies investigating that hypothesis are warranted. None. None declared. Conflicts of interest: The authors have no conflicts of interest to declare.

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