Sacroiliac joint (SIJ) involvement is a distinctive feature of spondyloarthritis (SpA). The main objective of this study was to assess the validity of color Doppler ultrasound (CDUS) in SIJ. This was a cross-sectional, blinded, case-control study of 108 cases divided into three groups: (a) 53 SpA patients with inflammatory back pain (IBP); (b) 28 SpA patients with no IBP; and (c) 27 healthy mechanical lumbar pain subjects. Physical examinations of the SIJs were assessed as positive or negative in each SIJ and were used as the gold standard. SIJs were examined with CDUS and spectral Doppler, and the SIJs were assessed as positive when both color Doppler and the resistance index (RI) were less than the cut-off point within the SIJs area. A total of 108 cases (53 female; mean age 36 ± 10 years old) were studied. The physical examination of the SIJs was positive in 38 patients (59 SIJs). Ultrasound detected Doppler signal within the SIJs in 37 cases (58 SIJs): 33 of them had symptomatic SpA (52 SIJs), 3 of them had asymptomatic SpA (5 SIJs), and 1 was a healthy control (1 SIJ). The accuracy of CDUS, when compared to physical SIJ examination, at the patient level in the overall group had a sensitivity of 70.3%, a specificity of 85.7%, a positive likelihood ratio of 4.9, and a negative likelihood ratio of 0.36. For the spectral Doppler RI, with an optimal cut-off point ≤0.75, the sensitivity was 76.2%, and the specificity was 77.8%. CDUS of SIJs seems to be a feasible and valid method for detecting active inflammation in patients with SpA.
Keywords: Diagnosis; Inflammatory back pain; Sacroiliitis; Spondyloarthritis; Ultrasound.