Magnetic resonance imaging assessment of axial psoriatic arthritis: extent of disease relates to HLA-B27

Objective: To determine the prevalence, on magnetic resonance imaging (MRI), of bone marrow edema lesions in symptomatic axial psoriatic arthritis (PsA), and to compare this prevalence with that in nonradiographic axial spondyloarthritis (SpA) and ankylosing spondylitis (AS) and its relationship to HLA-B27 status.

Methods: We performed a cross-sectional audit of MRI scans of lumbar spine (L-spine) and sacroiliac (SI) joints. Using the semiquantitative Leeds Scoring System in which bone marrow edema is graded from 0 to 3 according to severity of the lesions, MRI scans were scored independently by 2 expert readers who were blinded to the clinical characteristics of the patients. Concordant data from the 2 readers were used to report on definite lesions.

Results: MRIs from 76 patients with comparable age ranges were categorized into 3 groups: those from PsA patients, those from patients with nonradiographic axial SpA, and those from AS patients. HLA-B27 positivity was similar in PsA patients (10 of 33) and patients with nonradiographic axial SpA (10 of 24) and higher in AS patients (18 of 19). Total MRI scores (L-spine plus SI joints) were higher in AS patients than in PsA patients (P = 0.025) or in patients with nonradiographic axial SpA (P = 0.007). A relationship was seen between the severity and extent of disease and HLA-B27 positivity in PsA patients, which was comparable to that in AS patients. HLA-B27-negative PsA patients had lower MRI scores than HLA-B27-positive PsA patients (P = 0.03) and AS patients (P = 0.006), whereas scores were similar in HLA-B27-positive PsA patients and AS patients. Similarly, MRI scores of HLA-B27-negative patients with nonradiographic axial SpA were lower than those of AS patients (P = 0.01).

Conclusion: HLA-B27 positivity defines a group of patients with more severe axial bone marrow edema that is likely related to the classic AS phenotype. Clinically, HLA-B27-negative PsA is more likely to be reported as a "negative" MRI examination result.