Performance of Low-dose Computed Tomography, Magnetic Resonance Imaging and Conventional Radiography in Differentiating Axial Involvement in Patients with Psoriatic Arthritis

Abstract

Background: Sacroiliac joints (SIJ) radiography has lower sensitivity and specificity compared to magnetic resonance imaging (MRI) and low-dose CT (ldCT) of the SIJ for detecting axial spondyloarthritis. Whether this is also true for axial psoriatic arthritis (axPsA) remains uncertain. This study aimed to evaluate the performance of ldCT, MRI, and conventional radiography of SIJ and spine in distinguishing axial involvement in PsA patients. Methods: Fifty-one consecutive PsA patients (70.6% male, age 41 ± 13 years) meeting the CASPAR classification criteria, regardless of back pain, were included. All patients underwent SIJ and whole-spine radiography, SIJ MRI as well as SIJ ldCT, while 25 (49%) of 51 patients also underwent whole-spine MRI and ldCT. One rheumatologist with expertise in imaging and one trained reader evaluated images. The final diagnosis of axPsA was ascertained by two experienced rheumatologists. The sensitivity, specificity, and diagnostic accuracy of the three modalities for discriminating axPsA were compared. Results: AxPsA was diagnosed in 33.3% (17) of 51 patients. In discerning axial involvement in PsA patients, MRI exhibited superior sensitivity (92.9%) compared with ldCT (83.3%) and radiography (67.9%), while ldCT demonstrated higher specificity (97.1%) than MRI (86.4%) and radiography (72.7%). LdCT achieved the highest diagnostic accuracy (92%) among the three modalities, surpassing radiography (71%) and being comparable to MRI (89%). In the subgroup of patients with whole spine imaging, the combination of MRI and ldCT SIJ had the best diagnostic accuracy, reaching 93%. Including SIJ ldCT in addition to SIJ MRI further improved specificity (86.7% vs. 73.3%) with unchanged sensitivity (100%), while incorporating SIJ MRI alongside SIJ ldCT further improved sensitivity from 83% to 100%, with a modest decrease in specificity (86.7% vs. 93.3%). However, incorporating spine MRI/ldCT alongside SIJ MRI/ldCT did not further improve sensitivity or specificity in discriminating axial involvement in PsA patients. Conclusion: LdCT demonstrated superior diagnostic performance in distinguishing axial involvement in PsA patients compared to MRI or radiography, although MRI was more sensitive for detecting active sacroiliitis. The highest diagnostic performance was achieved with both MRI and ldCT of the SIJ. Additional spine imaging did not further increase diagnostic performance.