Peripheral spondyloarthritis and psoriatic arthritis <i>sine psoriase</i>: 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 <i>sine psoriase</i>). 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 <i>sine psoriase,</i> to determine if the two entities should be considered jointly or distinctly. Globally, pSpA appears to be more inclusive compared with PsA <i>sine psoriase</i> 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 <i>sine psoriase</i> have a higher prevalence HLA-Cw6, dactylitis and involvement of hand distal interphalangeal joints. Therefore, the difference between pSpA and PsA <i>sine psoriase</i> 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.