Elucidating the role of a positive family history in differentiating between axial and peripheral spondyloarthritis: an ancillary analysis of the ASAS-PerSpA study.

Objectives: Positive family history (PFH) of spondyloarthritis (SpA) is important in the diagnosis of SpA. However, the contribution of a PFH in differentiating the two SpA subtypes (axial and peripheral spondyloarthritis (pSpA)), in particular the importance of second-degree relative (SDR) has not been well-studied. We aimed to investigate whether PFH of radiographic axial spondyloarthritis (r-axSpA), psoriasis, uveitis, reactive arthritis and inflammatory bowel disease in first-degree relative (FDR) and second-degree relative (SDR) contributes to differentiation between axSpA and pSpA using the data from a multinational cohort study.

Methods: The ASAS-PerSpA study dataset was used to assess the effects of a PFH on differentiating between axSpA and pSpA via generalised structural equation modelling. Model building using backward selection was performed to obtain a final model. Direct, indirect and total effects of the path analysis were calculated.

Results: A total of 3803 patients were included: 2458 axSpA and 1345 pSpA patients. FDR (OR: 3.75, 95% CI: 2.86-4.91, p<0.001) and SDR (OR: 4.58, 95% CI: 3.19-6.59, p<0.001) with r-axSpA were positively associated while FDR (OR: 0.262, 95% CI: 0.207-0.331, p<0.001) and SDR (OR: 0.305, 95% CI: 0.221-0.420, p<0.001) with psoriasis were negatively associated with differentiating patients with axSpA from pSpA.

Conclusions: The presence of r-axSpA and psoriasis in FDR or SDR are useful in differentiating axSpA from pSpA. SDR with r-axSpA may contribute greater towards the differentiation than FDR. Clinicians should consider taking an extensive family history of SpA and their subtypes to better differentiate the subtypes within the SpA spectrum.