A novel diagnostic method (spectral computed tomography of sacroiliac joints) for axial spondyloarthritis

Background/Purpose To evaluate the diagnostic value of spectral computed tomography (CT) of sacroiliac joints for axial spondyloarthritis (SpA). Methods We retrospectively analyzed the records of 125 patients with low back pain (LBP) suspected of having SpA. Each patient underwent sacroiliac joint spectral CT examination. Water- and calcium-based material decomposition images were reconstructed. After 3–6 months of follow-up, 76 were diagnosed with SpA, and the remaining 49 patients were diagnosed with nonspecific LBP (nLBP). The slope of sacroiliac bone marrow HU (Hounsfield unit) curve ( λ HU ), CT value, and bone marrow to normal muscle ratios of water and calcium concentrations in the ilium and sacrum were calculated and compared between nLBP and SpA patients. Results The iliac λ HU was 8.26 ± 3.91 for nLBP and 9.81 ± 4.92 for SpA. The mean iliac ratios of water and calcium concentrations were 1.04 ± 0.03 and 21.67 ± 4.40, respectively, for nLBP, and 1.07 ± 0.04 and 111.5 ± 358.98, respectively, for SpA. The mean iliac CT values were 311.12 ± 86.52 HU for nLBP and 423.97 ± 127.51 HU for SpA. There were statistically significant differences in iliac ratios of water and calcium concentrations, CT value, and λ HU between nLBP and SpA patients ( p λ HU was the highest. The diagnostic odds ratio of ratio of iliac calcium concentration was the highest, and its negative likelihood ratio was the lowest. Conclusion Spectral CT not only shows bone erosion and sclerosis, but also shows and quantitatively measures bone marrow edema in the sacroiliac joints of SpA patients.