Diagnosing Oligoarticular Juvenile Idiopathic Arthritis in a Two-Year-Old: A Case Report.

Juvenile idiopathic arthritis (JIA) is a rare heterogeneous group of autoimmune disorders presenting in children and is characterized by persistent joint inflammation without a known cause. Here, we present the clinical course of a two-year-old girl who developed acute right knee swelling without preceding trauma. Laboratory findings, joint aspiration, imaging, and clinical diagnosis initially suggested reactive arthritis; however, the persistence of symptoms and the emergence of a second affected joint led to the diagnosis of oligoarticular JIA. Laboratory analysis revealed a markedly elevated antinuclear antibody (ANA) titer with a homogeneous pattern, supporting the diagnosis. The patient was treated with intra-articular corticosteroid injections after a multidisciplinary evaluation. This case underscores the importance of considering JIA in young children with persistent monoarthritis, highlighting its evolving presentation, and initiating early rheumatologic involvement to guide diagnosis, manage complications such as uveitis, and tailor treatment strategies.