Juvenile idiopathic arthritis (JIA) is a broad spectrum of disease defined by the presence of arthritis of unknown etiology, lasting more than six weeks duration, and occurring in children less than 16 years of age. JIA encompasses several disease categories, each with distinct clinical manifestations, laboratory findings, genetic backgrounds, and pathogenesis. JIA is classified into seven subtypes by the International League of Associations for Rheumatology: systemic, oligoarticular,

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... lar with and without rheumatoid factor, enthesitis-related arthritis, psoriatic arthritis, and undifferentiated arthritis. Diagnosis of the precise subtype is an important requirement for management and research. JIA is a common chronic rheumatic disease in children and is an important cause of acute and chronic disability. Arthritis or arthritis-like symptoms may be present in many other conditions. Therefore, it is important to consider differential diagnoses for JIA that include infections, other connective tissue diseases, and malignancies. Leukemia and septic arthritis are the most important diseases that can be mistaken for JIA. The aim of this review is to provide a summary of the subtypes and differential diagnoses of JIA. (J Rheum Dis 2017;24:131-137)