Psoriatic arthritis spectrum in children: a multicentre observational study.

OBJECTIVES: The aim of this study is to describe characteristics of children with the International League of Associations for Rheumatology (ILAR)-defined juvenile idiopathic arthritis (JPsA) and to assess whether more sensitive and specific criteria for defining JPsA can be identified. METHODS: A retrospective observational multicentre study was conducted including patients with a diagnosis of JPsA according to ILAR criteria. In this population, we identified clusters using as variables the clinical criteria of JPsA according to ILAR and the CASPAR clinical criteria. In addition, we defined as undifferentiated arthritis patients that met the ERA criteria, as defined by ILAR, and presented psoriatic features such as psoriasis or a history of psoriasis or psoriatic arthritis in a first-degree relative. RESULTS: 73 patients were enrolled. Three clinical clusters were found using unsupervised principal component analysis for the patients. Cluster 1 differed significantly for older patients and psoriasis. In contrast, Cluster 2 was mainly characterised by dactylitis and Cluster 3 was defined by family history of psoriasis and a significant prevalence of dactylitis. We also showed a statistically significant presence of familiarity for psoriatic arthritis in Cluster 2. The significance for all parameters evaluated did not change even when we included the patients with undifferentiated arthritis, except for MTX treatment, which was significantly more common in Cluster 2 (p=0.02), and tenosynovitis, also in Cluster 2 (p=0.05). Moreover, we evaluated our cohort by the Vancouver criteria. Combining the ILAR, CASPAR, and Vancouver criteria only two patients remain undifferentiated. CONCLUSIONS: Our study showed three clinical clusters with diverse demographic and clinical characteristics, indicating JPsA heterogeneity. The findings highlight the need to look beyond ILAR criteria for clinical variables, including family history of psoriatic arthritis. The ILAR, CASPAR, and Vancouver criteria improve the diagnosis of paediatric psoriatic spectrum arthritis. This complex disease population needs larger cohorts and clinical data, especially on axial involvement, to better categorisation and treatment.