Breakthrough improvement in the understanding of spondyloarthritis (SpA) has been witnessed in the past couple of decades, with an enhanced definition of the phenotype, clinical presentation, and therapies in this widely heterogeneous group of diseases.

The Assessment of SpondyloArthritis international Society (ASAS) has consecrated the classification of SpA patients into two categories according to the main clinical musculoskeletal symptom: predominantly axial (axSpA) and predominantly peripheral (pSpA) [1,2], with significant consequences on the treatment algorithm [3]. Although significant overlaps exist between these two categories, a recent cluster analysis of the peripheral manifestations in SpA (PerSpA) cohort, a worldwide cohort of 4465 SpA patients from 24 countries, has confirmed this classification, which made clinical sense again [4].

However, the peripheral SpA (pSpA) entity remains poorly defined in comparison with axSpA and psoriatic arthritis (PsA), as the clinical symptoms have low specificity, the biological markers are virtually lacking, and dedicated randomized controlled trials (RCTs) in this specific indication remain scarce [5,6]. Nevertheless, studies have shown that pSpA carries a prominent disease burden which contrasts with under-treatment compared with other SpA entities [7].

This review aims to summarize the current understanding of pSpA, its epidemiology, physiopathology, clinical diagnosis, and classification criteria. In addition, we present patient-reported outcomes used in pSpA clinical studies, available evidence on therapies, and future directions.