Pulling Apart Methods of Diagnosing Axial Psoriatic Arthritis, Back Pain

Diagnosis of axial spondyloarthritis (axSpA) and inflammatory back pain among patients with psoriatic disease may vary between whole spine MRI and classification-defined criteria, according to study findings published in RMD Open: Rheumatic & Musculoskeletal Diseases.

Despite high prevalence of axial disease among patients with psoriatic arthritis (PsA), no accepted definition for the condition exists, in which treatment recommendations are based from those of ankylosing spondylitis (AS).

Moreover, researchers note that studies comparing axial PsA with AS have found notable differences in the former, including lower prevalence and intensity of inflammatory back pain (IBP), spinal mobility restriction and radiographic sacroiliitis, and more frequent asymmetric spine and sacroiliac joints (SIJ) involvement.

“While imaging evidence of sacroiliitis or spondylitis is desirable for identifying patients with axial involvement, radiographic diagnosis has low inter-reliability and intra-reliability,” they added. “MRI has become an essential tool for axSpA diagnosis and MRI sacroiliitis is included in the classification criteria for axSpA. Only a few small studies have investigated axial findings by MRI among patients with PsA.”

Deriving whole spine and SIJ MRI data, the study authors examined inflammatory and structural lesions consistent with SpA in patients with PsA and in those with psoriasis with clinical suspicion of axPsA (N = 93; 69.9% PsA), and their correlation with clinical features and axSpA classification criteria.

In the cross-sectional retrospective analysis, MRI spondylitis and/or sacroiliitis (MRI-SpA) was defined according to Assessment of Spondyloarthritis International Society (ASAS) consensus and by radiologist impression. Considering MRI as the gold standard, agreement between MRI-SpA and different IBP definitions (Berlin/ASAS/rheumatologist criteria) and the axSpA classification criteria were calculated.

Of the study cohort, the majority of patients experienced back pain (81.7%), in which 57% of patients were found to have IBP by the rheumatologist impression and 36.6% according to both ASAS and Berlin criteria.

Comparably, overall prevalence of MRI findings consistent with SpA was low, with MRI-SpA found in 9.7% of patients by ASAS definition and in 12.9% by radiologist impression, of which 25% had isolated spondylitis. Low agreement was identified between the 3 IBP definitions and MRI-SpA.

“IBP definition by rheumatologist had a higher sensitivity for MRI-SpA by ASAS and radiologist (50%-55.6%) but with low specificity (42%-42.9%), while Berlin and ASAS IBP criteria had higher specificity for MRI-SpA by ASAS and radiologist (61.9%-63%) but with low sensitivity (22.2%-33.3%),” they noted.

Furthermore, late onset of back pain or asymptomatic patients were identified to account for most cases with MRI-SpA not meeting axSpA or IBP criteria. Findings of the univariate and multivariable regression analyses additionally identified male sex as being the only variable to be associated with radiologist-MRI-SpA (OR, 6.91; 95%CI, 1.42-33.59).

“Clinical and epidemiological differences between axPsA and other axSpA may explain these findings,” concluded researchers. “Current efforts to study axial involvement in PsA led by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and ASAS should help to define this entity in patients with PsA.”

Reference

Diaz P, Feld J, Eshed I, Eder L. Characterising axial psoriatic arthritis: correlation between whole spine MRI abnormalities and clinical, laboratory and radiographic findings. RMD Open. 2022;8:e002011. doi:10.1136/ rmdopen-2021-002011