When it's not juvenile idiopathic arthritis: unmasking monogenic mimickers in children monogenic mimickers of chronic arthritis.

Chronic arthritis in children is widely associated with juvenile idiopathic arthritis (JIA); however, several rare monogenic disorders may mimic its clinical presentation. Misdiagnosis can result in unnecessary immunosuppressive treatment and delay appropriate care. This study aimed to share our experience with monogenic disorders presenting as chronic arthritis and highlight their distinguishing clinical and imaging features. This retrospective cohort study included patients initially suspected of having JIA who were later diagnosed with a monogenic disorder. Clinical, laboratory, imaging, and genetic data were also collected and evaluated. Among the 25 patients, the most frequent diagnoses were progressive pseudorheumatoid dysplasia (PPRD; n = 12) and camptodactyly arthropathy-coxa vara-pericarditis (CACP) syndrome (n = 8). Other diagnoses included mucolipidosis type III gamma, primary hypertrophic osteoarthropathy (PHO), and multicentric carpotarsal osteolysis (MCTO). While all PPRD and CACP patients had biallelic pathogenic variants in CCN6 and PRG4, respectively, PHO and MCTO were associated with monoallelic mutations. Common misdiagnoses included polyarticular JIA, leading to the inappropriate use of methotrexate or biologic agents.

conclusionSeveral monogenic disorders can mimic JIA in pediatric patients, leading to diagnostic challenges. Clinical features, such as camptodactyly, skeletal deformities, digital clubbing, median nerve neuropathy, and poor response to treatment should prompt further evaluation, including genetic testing. Increased awareness and early recognition of these conditions are crucial to avoid unnecessary immunosuppression and improve patient outcomes. WHAT IS KNOWN: • Several rare monogenic disorders can clinically mimic JIA and misdiagnosis of these monogenic mimickers may lead to inappropriate immunosuppressive treatment and delayed appropriate care. WHAT IS NEW: • This study presents a real-world single-center data that systematically characterizes five distinct monogenic disorders mimicking JIA. • Findings emphasize the importance of early suspicion, especially in cases with symmetrical interphalangeal involvement (PPRD), camptodactyly with hip deformity (CACP), or osteolysis with renal/facial anomalies (MCTO), to avoid unnecessary immunosuppression.