Prevalence of non-radiographic sacroiliitis in patients with psoriatic arthritis: a real-life observational study.

Objective To establish the prevalence of non-radiographic sacroiliitis within a real-life sample of patients with psoriatic arthritis (PsA), using pelvic radiographs and magnetic resonance imaging (MRI) of sacroiliac joints (SIJ). Methods This cross-sectional study included 107 consecutive adults with PsA (CASPAR criteria). Participants completed clinical and laboratory evaluation, pelvic radiographs scored for radiographic sacroiliitis according to the modified New York (NY) criteria, and noncontrast MRI of SIJ, scored by Berlin score and categorized into active sacroiliitis using the 2016 Assessment of Spondyloarthritis International Society (ASAS) criteria and structural sacroiliitis. Results Radiographic sacroiliitis/NY criteria was detected in 28.7% (n=29), confirmed by MRIdetected structural lesions in 72.4% (n=21). Active sacroiliitis was detected by MRI in 26% (n=28) of patients, with 11% (n=11) qualifying for non-radiographic sacroiliitis. Patients with radiographic and non-radiographic sacroiliitis had similar clinical characteristics, except of a longer duration of psoriasis and PsA in the radiographic subgroup, 23.8±12.5 vs 14.1±11.7, p=0.032 and 12.3±9.8 vs 4.7±4.5 years, p=0.019, respectively. Inflammatory back pain (IBP) was reported in 46.4% (n=13) with active sacroiliitis and 27% (n=3) with non-radiographic sacroiliitis. The sensitivity of IBP for detection of non-radiographic was low (27%) and moderate for radiographic sacroiliitis (52%), whereas specificity ranged from 72 to 79%, respectively. Conclusion The prevalence of active sacroiliitis among a real-life population of patients with PsA was 26%. However, the prevalence of non-radiographic sacroiliitis was low (11%) compared to radiographic sacroiliitis (28.7%) seen in patients with longer disease duration. IBP was not a sensitive indicator for the presence of early stage sacroiliitis that was commonly asymptomatic.