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Juvenile idiopathic arthritis (JIA) refers to a group of disorders that are a major cause of chronic arthritis in children. It is the most common chronic rheumatic disease of childhood and can be a significant cause of both short-term and long-term disability. In the United States, approximately 294,000 children younger than 18 years have arthritis or other rheumatic conditions.

JIA is relatively common compared to other chronic diseases of childhood. There are as many children with juvenile-onset diabetes as there are those with juvenile-onset arthritis, and there are 10 times as many children with arthritis as there are children affected with muscular dystrophy.

Essentials of Diagnosis

  • Six weeks or more of persistent joint swelling, and the exclusion of other causes of arthritis in childhood.
  • There is no specific laboratory test that either confirms or excludes JIA.
  • The type of JIA is determined by the age of the child at onset of symptoms; the number and type of joints involved; the presence of extra-articular symptoms, such as rash, fever, and iritis; and the course of the illness during the first 6 months after the diagnosis is confirmed.
  • Significant complications, including macrophage activation syndrome (MAS), contractures, growth retardation, and visual loss, can be avoided by prompt diagnosis and treatment.

According to the International League Against Rheumatism, the types of JIA can be classified as oligoarticular, polyarticular (including seropositive and seronegative), systemic onset (SOJIA), psoriatic, enthesitis-related, and undifferentiated. The different subtypes of JIA are mainly determined by the pattern of joint involvement at the onset of the illness.

The subtypes of JIA are identified and classified based on the following factors: age at onset, number of joints involved initially, rheumatoid factor status, and associated extra-articular symptoms (Table 20–1). Identification of the correct subtype helps guide appropriate therapy and determine prognosis.

Table 20–1. Comparing the Features of the Subgroups of Juvenile Idiopathic Arthritis.

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