Psoriatic juvenile idiopathic arthritis: a tale of two subgroups

Purpose of review The International League of Associations for Rheumatology criteria parse out juvenile idiopathic arthritis (JIA) into seven groups, with the aim of creating homogeneous subgroups suitable for clinical and research evaluation. However, prior studies have shown that psoriatic JIA (psJIA) may be a heterogeneous entity. Recent findings PsJIA is composed of two subgroups, differentiated by age at onset. Older children with psJIA have features of spondyloarthritis, including relative male preponderance, increased risk of axial involvement, and enthesitis. Extrapolating from studies on adults with psoriatic arthritis, the mechanism of older-onset PsJIA appears to involve autoinflammatory dysregulation centered at the synovial-entheseal complex; there may also be a role for gut inflammation in a subset of patients. In contrast, patients with early-onset PsJIA bear similarities to early-onset oligoarticular and polyarticular JIA patients, including female preponderance, antinuclear antibody (ANA) positivity, and certain human leukocyte antigen types, suggesting a possible role for traditional autoimmune mechanisms. Both groups, however, share a high frequency of dactylitis. Summary This review demonstrates that PsJIA is a heterogeneous entity, with different clinical, genetic, and possibly pathophysiological features. Future studies are needed to explore the mechanisms of arthritis in both subgroups, particularly in the early-onset children.