Comparative analysis of whole spine and sacroiliac joint magnetic resonance SPARCC scores in patients with SAPHO syndrome and ankylosing spondylitis.

BACKGROUND

Ankylosing spondylitis (AS) and SAPHO syndrome both involve the spine and sacroiliac joints with bone marrow edema (BME) on MRI, which can lead to spinal structural damage. No previous study has compared BME characteristics between the two diseases.

METHODS

42 SAPHO and 60 AS patients with spinal or sacroiliac involvement underwent whole-spine and sacroiliac MRI. SPARCC scores for each spinal segment and sacroiliac joints, vertebral unit involvement frequency, and BME range, intensity, depth were compared. Correlation between SPARCC scores of the whole spine and sacroiliac joints and clinical indicators were analyzed in the two groups of patients.

RESULTS

SPARCC scores for all spinal segments and sacroiliac joints in AS patients were significantly higher than those in SAPHO syndrome patients (P < 0.01). Defining bone marrow edema as SPARCC score > 0, the positive rate of vertebral units in spinal segments and sacroiliac joints was higher in AS than in SAPHO syndrome (P < 0.05). The incidence of BME in the cervical, thoracic, and sacroiliac joints was higher in AS than in SAPHO syndrome (P<0.001), with no significant difference in the incidence of lumbar spine BME (P > 0.05); the incidence of bilateral sacroiliac joint edema also showed no intergroup difference (P > 0.05). Further analysis of the score composition in SPARCC-positive cases revealed: the extent scores for each spinal segment in AS patients were higher than those in the SAPHO group (P < 0.001), while there were no significant differences in intensity and depth scores between the two groups; in the sacroiliac joints, the extent score was higher in the AS group (P < 0.05), but the intensity score was higher in the SAPHO group (P < 0.05). Correlation analysis in AS and SAPHO patients showed: spinal SPARCC scores in AS patients were positively correlated with ESR, CRP, and ASDAS-CRP; spinal SPARCC scores in SAPHO patients were positively correlated with BASFI and BASMI. In subgroup analysis, AS patients showed positive correlations between spinal SPARCC scores and ASDAS-CRP at both thresholds (≥2, ≥3), and sacroiliac joint SPARCC scores were positively correlated with BASDAI at both thresholds; at threshold ≥3, sacroiliac joint SPARCC scores were also positively correlated with ASDAS-CRP. In SAPHO patients, at threshold ≥2, spinal SPARCC scores were positively correlated with VAS, BASFI, and BASMI; at threshold ≥3, spinal SPARCC scores were only positively correlated with BASFI, and sacroiliac joint SPARCC scores were positively correlated with ASDAS-CRP (all P < 0.05).

CONCLUSIONS

SAPHO and AS show similar BME characteristics on MRI. SAPHO patients have a smaller extent of BME in spine and sacroiliac joints, whereas spinal BME may have a stronger correlation with their physical function. In SAPHO patients with axial involvement, the treatment experience of SPA may have certain reference value.