Peripheral spondyloarthritis and psoriatic arthritis sine psoriase: are we dealing with semantics or clinically meaningful differences?

Diagnosing peripheral spondyloarthritis (pSpA) remains a significant challenge due to the lack of specific disease biomarkers and the overlap with other SpA subtypes, mainly psoriatic arthritis (PsA), which represents a diagnostic challenge particularly in the absence of skin psoriasis (PsA sine psoriase). This narrative review aimed to compare the epidemiology, genetic susceptibility, pathophysiology, classification criteria, disease phenotype and burden, and therapeutic guidelines between patients diagnosed with pSpA and those with PsA sine psoriase, to determine if the two entities should be considered jointly or distinctly. Globally, pSpA appears to be more inclusive compared with PsA sine psoriase. Areas of similarities include age of onset, number of joints involved and prevalence of axial involvement. However, patients with pSpA have a male gender predominance, a higher prevalence of HLA-B27, enthesitis and involvement of large joints of the lower limbs, whereas patients with PsA sine psoriase have a higher prevalence HLA-Cw6, dactylitis and involvement of hand distal interphalangeal joints. Therefore, the difference between pSpA and PsA sine psoriase goes beyond semantics. The few dissimilarities should drive scientific efforts to reach a better characterisation of pSpA as an individual disease. Accordingly, randomised clinical trials should target patients with well-defined pSpA to identify effective therapies in this population.