Computed tomography scanning facilitates the diagnosis of sacroiliitis in patients with suspected spondylarthritis: Results of a prospective multicenter French cohort study

Objective To assess the performance of computed tomography (CT) scanning for ascertaining sacroiliitis in patients with suspected spondylarthritis (SpA). Methods The Echography in Spondylarthritis French cohort consists of 489 patients with suspected SpA. At baseline, all patients underwent clinical examination, HLAB typing, and pelvic radiography. Pelvic CT scanning was performed if sacroiliitis on radiography was considered uncertain or if patients presented with buttock pain duration of >6 months. A set of 100 paired radiographs and CT scans was read in a blinded manner by 2 radiologists, and the kappa coefficient was used to assess their interreader reliability. One of the radiologists read the 173 available pairs of radiographs and CT scans performed at baseline. Results After training, interreader reliability was moderate for sacroiliitis grading on radiographs (? = 0.59), excellent on CT scans (? = 0.91), and excellent for ascertaining sacroiliitis on both radiographs (? = 1) and CT scans (? = 0.96). The first and second readers considered the quality of imaging to be excellent in 66% and 67%, respectively, of the radiographs (? = 0.88) and in 93% and 92%, respectively, of the CT scans (? = 0.93). Concordance between radiographs and CT scans was low for sacroiliitis grading (? = 0.08) or ascertainment (? = 0.16). Definite sacroiliitis was ascertained on radiographs in 6 patients (3.5%) (confirmed by CT scans in 4 patients) and on CT scans in 32 patients (18.5%). A history of uveitis was associated with definite sacroiliitis on radiographs (P = 0.04) and CT scans (P < 0.0001). Conclusion Definite sacroiliitis was underestimated by radiography, as compared to CT scanning. CT scanning should facilitate the diagnosis of ankylosing spondylitis in patients with suspected SpA.