Background Psoriatic arthritis (PsA) shows the largest complexity in joint involvement among all inflammatory types of arthritis.
Objectives We aimed at comparing a feasible number of data-driven joint involvement (JI) groups in the Swiss Clinical Quality Management (SCQM) PsA cohort with the classical subtypes of PsA as described by Moll & Wright (M&W). Also, we compared these new PsA subgroups in their clinical response to TNF-blockade, the current gold standard of disease modification in respect of structural damage.
Methods By December 1st 2013, we included all 1380 patients in the SCQM registry with PsA diagnosis. Hierarchical clustering was applied to generate distinct groups of patients based only on their tender or swollen joint involvement. The robustness of clustering was tested by comparing swollen (SJ) and tender joint (TJ) clusters, and by repeated clustering with different linkage methods. Analyses were repeated in the subgroup of 872 PsA patients fulfilling the CASPAR classification criteria.
Results Ward's Minimum Variance method for clustering gave the most distinguished clusters and will be reported in the following results. In both SJ and TJ four clusters were found characterizing oligoarticular, hand or foot predominant, and polyarticular features (Fig. 1). On the individual patient level, about one third of joints were affected in a symmetric manner. Assignment of patients to the same clusters in SJ and TJ varied between 85% (oligoarticular) to 17% (polyarticular). In the following, only SJ results are reported. Most patients assigned to the oligoarticular cluster were also of the oligoarticular M&W subtype (78%). The rest of patients in the oligoarticular cluster were in the symmetric (11%) or DIP (2%) M&W subtypes or were not assignable to these subtypes (9%). In the polyarticular cluster, MCP and PIP joints were more frequently involved than DIP joints, but osteoproliferation, typically juxta-articular to DIP joints, was also overrepresented (49%, p<0.001). Dactylitis was most prevalent in cluster D, but clinical improvements upon TNF blockade were similar among the groups.
Conclusions We identified a small but highly characteristic cluster of patients with more extended joint, bone and skin involvement, but all obtained clusters were similar with regard to response to TNF-blockade.
Disclosure of Interest None declared
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