Background Psoriatic Arthritis (PsA) is a heterogeneous disease with a variable, sometimes evolving clinical phenotype. An estimated 25-70% of patients may have spinal involvement which varies from largely asymptomatic to severe inflammatory back pain which may be undistinguishable from Ankylosing Spondylitis (AS). The utility of MRI in the diagnosis and assessment of spinal disease in AS and axial SpA (axSpA) is now well proven. It is however unclear whether MR appearances of spinal involvement differ between patients with axSpA or AS and patients with PsA related spondylitis.
Objectives To report the MRI prevalence of bone marrow oedema (BMO) lesions in symptomatic back pain in patients with PsA in comparison with axSpA and AS.
Methods Cross-sectional audit of MRI scans of the lumbar spine (LS) and sacroiliac joints (SIJs) requested consecutively between 2007-2011 in the rheumatology service of a large teaching hospital to reflect service development. Scans were retrived and clinical notes were consulted to confirm clinical diagnosis according to requesting clinician, HLA-B27 status and demographics. MRI scans were scored independently by 2 expert readers, blinded to the clinical characteristics of the patients using the semiquantitative Leeds Scoring System for BMO lesions representative of inflammation in the spine and SIJs, whereby a lesion graded as moderate (grade ≥2) is considered clinically significant (1). Concordant data from the two readers were used to report on definite lesions.
Results MRI scans from 76 patients were available for analysis. Subjects were categorized into 3 groups: PsA, axSpA (patients fulfilled the ASAS criteria for axial SpA but not the modified New York criteria for AS) and AS (if patients fulfilled the mNYC). Age was comparable in all groups [median (range) for PsA: 39 (18-60); axSpA: 34,5 (19-47); AS: 35,5 (23-61)]. There were more females in the PsA group (25/33 vs 8/21 in SpA and 6/19 in AS groups). HLA-B27 positivity was similar in PsA (10/33) and axSpA (10/24) and higher in AS (18/19). Total MRI scores (LS+SIJ) were higher in AS patients compared to PsA (p=0.025) and axSpA (p=0.007). Comparable amount of disease extent was shown by similar total number of BMO lesions both at the SIJ and LS in PsA, axSpA and AS patients but the number of severe lesions at the LS (grade ≥2) was higher in AS (p=0.01) and in PsA (p=0.03) than axSpA. When the groups were sub-analysed according to HLA-B27 status, a relationship was seen between the severity and extent of disease and HLA-B27 in the PsA group which was comparable to the AS group. HLA-B27 negative PsA patients had lower MRI scores than HLA-B27 positive PsA (p=0.03) and AS patients (p=0.006) whereas HLA-B27 positive PsA patients had similar scores to AS. Similarly MRI scores of HLA-B27 negative axSpA patients were lower than AS (p=0.01) despite the similar MRI scores observed between HLA-B27 positive axSpA and AS groups.
Conclusions HLA-B27 related active PsA spondylitis shows a similar degree of MRI bone oedema as AS with a lesser degree of bone oedema in HLA-B27 negative PsA. These results suggest that the HLA-B27 subgroup of PsA share common aetiopathogenic mechanisms of disease with AS.
Marzo-Ortega, H, et al. Ann Rheum Dis 2009;68:1721–1727.
Disclosure of Interest None Declared
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