Background/Purpose: Patients with a clinical diagnosis of Spondyloarthritis (SpA) and Psoriatic Arthritis (PsA) may have predominant axial or predominant peripheral symptoms. However, a huge clinical overlap exists and clear patterns of distribution are lacking. The objective of this study was to identify patterns of peripheral involvement according to the specific location of these symptoms in the whole spectrum of SpA and PsA.

Methods: International, cross-sectional and multicentre study with 24 participating countries. Consecutive patients considered by their treating rheumatologist as suffering from either PsA, axial SpA (axSpA), peripheral SpA (pSpA), inflammatory bowel disease (IBD)-related SpA, reactive arthritis or juvenile SpA were enrolled. A specific cluster analysis for each peripheral musculoskeletal manifestation (i.e., peripheral articular involvement, enthesitis and dactylitis) was conducted using data concerning the specific location of these symptoms at any time during the course of the disease. Multiple correspondence analyses and k-means clustering methods were used. Distribution of peripheral manifestations and clinical characteristics were compared across the different clusters.

Results: A total of 4465 patients were included in the analysis. Three clusters were found with regard to the location of peripheral articular involvement (Fig. 1), labelled as “infrequent arthritis (a)”, “predominantly lower limbs (b)” and “predominantly hands (c)”. Patients from the “a” group showed, in comparison with “b” and “c” groups, a higher prevalence of males (63.9% vs 51.3% vs 41.5%), HLA-B27 positivity (79.8% vs 48.2% vs 34.8%) and SpA diagnosis (axSpA or pSpA) (76.7% vs 30.6% vs 35.2%), but lower prevalence of psoriasis (23.2% vs 67.8% vs 59.6%) and PsA diagnosis (17.2% vs 61.7% vs 58.5%). Between “b” and “c” clusters, the first one showed a higher prevalence of uveitis (15.7% vs 8.7%), and a lower prevalence of IBD (3.5% vs 6.7%).
With regard to the location of enthesitis (Fig. 2), 3 clusters were also found, labelled as “predominantly heel enthesitis (d)”, “predominantly axial enthesitis (e)” and “polyenthesitis (f)”. Patients from the “f” group showed a higher prevalence of fibromyalgia according to the FiRST questionnaire (41.3% vs 17.4% vs 31.3%), psoriasis (48.3% vs 28.4% vs 23.4%) and PsA diagnosis than in the “d” and “e” groups (40.8% vs 22.7% vs 21.5%), and a lower prevalence of males (40% vs 61.9% vs 56.2%) and SpA diagnosis (52.5% vs 71.0% vs 73.1%).

Finally, 3 clusters were found with regard to the location of dactylitis, labelled as “absence of dactylitis (g)”, “predominantly toes (h)” and “predominantly fingers (i)”. The “g” group showed in comparison with the other two groups, the highest prevalence of males (61.4% vs 51.4% vs 52.9%), HLA-B27+ (66.6% vs 52.5% vs 50.0%) and SpA diagnosis (72.1% vs 30.7% vs 41.2%), and the lowest prevalence of psoriasis (26.9% vs 68.6% vs 79.4%) and PsA diagnosis (21.5% vs 65.7% vs 52.9%).

Conclusion: These results suggest the presence of heterogeneous patterns of peripheral involvement in SpA and PsA patients without clearly defined groups, confirming the clear overlap of these peripheral manifestations across the different underlying rheumatological diseases.

Figure 1. Cluster analysis for peripheral articular involvement: distribution of the affected joints with regard to the cluster.

Figure 2. Cluster analysis for enthesitis: distribution of the affected enthesis with regard to the cluster.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-of-clinical-phenotypes-in-patients-with-axial-spondyloarthritis-peripheral-spondyloarthritis-and-psoriatic-arthritis-according-to-peripheral-musculoskeletal-manifestations-a-cluster-a/