Artritis idiopática juvenil de inicio sistémico, un reto diagnóstico: reporte de caso

Introduction: Juvenile idiopathic arthritis (JIA) is the leading cause of chronic arthritis in childhood; however, its diagnosis can be difficult. This article aims to describe the diagnostic process from a patient with systemic JIA. Case presentation: Male patient of 14 months of age, with 15 days of daily fever up to 40^oC; the fever was refractory to antipyretic management and was associated with irritability and hyporexia. He received antimicrobials on suspicion of hidden bacteremia. Five days later, polymorphic erythema was added, so it was considered Kawasaki disease, receiving gammaglobulin but without clinical response. After 24 days of evolution, fever and arthritis persisted; Magnetic resonance imaging revealed intraarticular effusion in both knees and left hip, with no evidence of osteomyelitis. In synovial fluid of the right knee an increase of polymorphonuclear cells was detected, reason why septic arthritis was considered, initiating vancomycin. He was sent to another hospital because of the persistence of the condition; it was confirmed the fever and the maculopapular, generalized, not pruritic exanthema, which predominated on the trunk. Up to 40 days of evolution, the diagnosis of systemic JIA was confirmed and treatment with systemic steroids was initiated. One week later, tocilizumab and methotrexate were added because the symptoms remained unchanged. With this treatment the remission of fever and exanthema was achieved, as well as improvement of the joint symptoms. Conclusion: JIA is a disease that shares clinical signs and symptoms with different diseases. In general, due to the non-specific nature of the clinical picture and the lack of laboratory or imaging studies to confirm it, the diagnosis in young children is made by exclusion.