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Psoriatic spondyloarthritis forms part of the spondyloarthritis spectrum, between peripheral-only psoriatic arthritis and ankylosing spondylitis. Also, although it is less severe radiographically than ankylosing spondylitis, psoriatic spondyloarthritis has a similar disease burden in terms of most indices, according to results of a single-center, cross-sectional observational study conducted among consecutive psoriatic arthritis and ankylosing spondylitis patients.
The study, published in the Annals of the Rheumatic Diseases, reported that psoriatic spondyloarthritis (PsSpA) shares features of both psoriatic arthritis and ankylosing spondylitis, including axial arthritis, peripheral arthritis and enthesitis. Prior comparative studies are few and often of small sample size; findings have not been entirely consistent.
To further define similarities and differences, and to see if these could be explained by clinical and genetic parameters, Jadon, et. al. prospectively compared the prevalence, clinical and radiographic characteristic of PsSpA in psoriatic arthritis with AS in 402 cases (201 with PsA; 201 with AS).
After examination of axial radiographs, participants were reclassified as PsSpA (n=118; 29.35%) based upon psoriasis (past/present) and inflammatory radiographic axial disease (RAD); pPsA (n=127; 31.60%) based upon psoriasis (past/present), peripheral arthritis and no RAD; and AS (n=157; 39.05%) based upon mNY criteria for AS and no psoriasis (past/present). A substantial proportion of patients with RAD had PsSpA (118/275; 42.91%).
Jadon, et al. found predictors of psoriatic spondyloarthritis in their psoriatic arthritis cohort to include: the presence of HLA-B*27, younger age at arthritis onset, higher nail onycholysis severity, axial inflammatory symptoms and the presence of irritable bowel syndrome.
The authors emphasized, “PsSpA is not a clinically less impactful form of AS,” pointing out that measures of disease activity (ASDAS, BSDDAI, PaGA), disability (HAQ) and metrology (BASMI) were high among psoriatic spondyloarthritis and AS cases, without statistically significant differences between them. Peripheral arthritis was observed in 74% of PsSpA cases, and erosions were observed in 64% (48/75) of those with available radiographs. The additional burden of peripheral joint disease, therefore, may have influenced some of the measure.
The finding that psoriatic spondyloarthritis is part of the SpA spectrum and that it is associated with similar disease burden as ankylosing spondylitis (AS) despite less radiographic severity, the authors concluded, “may be of relevance in the development of future treatment guidelines.” They note further that “PsSpA may represent a distinct endophenotype influenced by factors related to the presence of psoriasis, psoriatic nail disease and HLA-B*27 variants.”
Because the study was conducted in a secondary care hospital among unselected psoriatic arthritis and AS referrals, the findings may be considered to be generalizable, Jadon, et al. suggest. Finally, future research will explore whether genetic variants are linked closely with more homogeneously defined disease patterns.
Deepak R Jadon, Raj Sengupta, et al. "Axial Disease in Psoriatic Arthritis study: defining the clinical and radiographic phenotype of psoriatic spondyloarthritis," Annals of the Rheumatic Diseases. Dec. 2, 2016. DOI: 10.1136/annrheumdis-2016-209853