Juvenile idiopathic arthritis (JIA) is a clinically heterogeneous group of arthritides that are characterized by onset before 16 years of age and defined in part as lasting ≥6 weeks.1 Significantly, the etiology of JIA is unknown, making it a diagnosis of exclusion.2
The most common autoimmune condition of childhood, JIA has a prevalence of 3.8 to 400 affected children for every 100,000 people.3,4 As the leading cause of musculoskeletal disability in children,5 and comprising 7 categories of disease, JIA must be managed with appropriate initial and ongoing intervention.
The amalgam of care that a JIA patient requires—medical, social, physical, psychological—calls for a primary care physician’s expert ability to collaborate and coordinate with medical specialists and subspecialists, including rheumatology, ophthalmology, social work, physical and occupational therapy, and psychology. The goal? As this article describes, the goal is to provide prompt diagnosis, suitable and effective intervention, and continuity of care. (JIA is a lifelong disease, in many cases.)
How JIA is classifiedfor diagnosis and treatment
JIA comprises 7 categories, or classes.6 The scheme devised by the International League of Associations for Rheumatology (ILAR), now widely accepted, classifies JIA on the basis of clinical and biochemical markers that aid detection and treatment of the disorder, as well as research. (See “How efforts to classify JIA have caused confusion.”7-10) The ILAR classes (TABLE11) are:
- enthesitis-related arthritis (ERA)
- extended oligo-articular JIA (eoJIA), which involves ≤4 joints
- juvenile psoriatic arthritis (jPsA)
- rheumatoid factor (RF)-positive polyarticular JIA (RF+ pJIA)
- RF-negative polyarticular JIA (RF– pJIA)
- systemic-onset JIA (sJIA)
- undifferentiated JIA, which, generally, involves ≥4 joints.
How efforts to classiy JIA have caused confusion7-10
Various classifications of juvenile arthritis have been proposed and used over the past 3 decades. First was the American College of Rheumatology’s 1972 criteria for juvenile rheumatoid arthritis7; next came the European League against Rheumatism (EULAR) criteria for juvenile chronic arthritis, developed in 1977.8 Being contemporaneous, the 2 classifications led to a complicated, dichotomous definition of JIA among clinicians and researchers.
As a result of this disarray, the 1997 Durban, South Africa, meeting of the Pediatric Standing Committee of the International League of Associations for Rheumatology (ILAR)9 proposed that juvenile idiopathic arthritis be adopted as the umbrella term for the misunderstood terms juvenile rheumatoid arthritis and juvenile chronic arthritis. The intent of including “idiopathic” in the term was to acknowledge that the cause of these diseases was (and is still) unknown.
The novel classification proposed by the Pediatric Standing Committee was followed, in 2001, by an ILAR task force meeting in Edmonton, Alberta, Canada, on the classification of childhood arthritis. The outcome was a recommendation to add exclusion and inclusion criteria, to make all classes of JIA mutually exclusive.10 Most recently, as discussed in the body of this article, updated ILAR guidelines on JIA classification emphasize 1) heterogeneity among the 7 disease subtypes and 2) the fact that overlapping and exclusive features exist from class to class.
Updated guidelines regarding the 7 ILAR classes of JIA emphasize heterogeneity among disease subtypes, with overlapping and exclusive features noted from class to class.11
Extended oligo-articular JIA (27%-56%), pJIA (13%-35%), sJIA (4%-17%), and ERA,(3%-11%) are the most common JIA subtypes,12 with age of onset and sex predilection differing according to JIA class.11 The disease occurs more often in girls than in boys,11 and the predisposition is higher among Whites and Asians. The incidence of JIA (all classes taken together, for every 100,000 people) is: in Japan, 10 to 15 cases13; in Turkey, 64 cases14; in Norway, 65 cases15; and in the United States and Canada, taken together, 10 to 15 cases.16
What causes JIA?
The etiology of JIA remains unclear. It is known that the disease involves inflammation of the synovium and destruction of hard and soft tissues in joints.17 It has been postulated, therefore, that a combination of genetic, environmental, and immunogenic mechanisms might be responsible for JIA.
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