When juvenile idiopathic arthritis is not inflammatory: a case-based review of camptodactyly–arthropathy–coxa vara–pericarditis syndrome in early childhood

Juvenile idiopathic arthritis (JIA) is the most common cause of chronic arthritis in childhood; however, not all early-onset arthropathies are inflammatory. We report the case of a 4-year-old girl initially diagnosed with oligoarticular JIA and treated with methotrexate and subsequently with a tumor necrosis factor inhibitor, without significant clinical improvement and despite persistently normal inflammatory markers. Clinical reassessment raised suspicion of a non-inflammatory arthropathy, supported by characteristic radiographic findings, including metaphyseal flaring of the distal femora and proximal tibiae. Genetic evaluation identified compound heterozygous pathogenic and likely pathogenic variants in the PRG4 gene, confirming the diagnosis of camptodactyly–arthropathy–coxa vara–pericarditis (CACP) syndrome (OMIM #208250). This case highlights common diagnostic pitfalls in pediatric practice and emphasizes the importance of considering genetic, non-inflammatory causes of chronic arthropathy when clinical, laboratory, and therapeutic features are atypical for JIA. Early recognition of CACP syndrome prevents unnecessary immunosuppression and allows appropriate multidisciplinary management.