A 2-year-old Caucasian girl has had left knee swelling for 2 months (Figure 172-1). On physical examination, she has a warm left knee with limited range of motion and an effusion. Her left leg is longer than her right, and she walks with an antalgic gait. She has no other systemic signs and symptoms. Her antinuclear antigen (ANA) test is positive (1:160, speckled pattern) and her erythrocyte sedimentation rate is normal. She is diagnosed with oligoarticular juvenile idiopathic arthritis (oligoJIA). After initially taking nonsteroidal antiinflammatory medication around the clock, she is given an intra-articular steroid injection to treat her synovitis followed by physical therapy. Six weeks later, her knee exhibits full range of motion and is free of swelling. Six months later, she is found to have anterior uveitis (Figure 172-2) on routine screening slit lamp ophthalmology exam. Her uveitis is treated with ocular steroid drops, but her eye disease remains active, and requires the disease modifying antirheumatic drug, methotrexate.
Juvenile Idiopathic Arthritis (JIA), the most common chronic rheumatologic disease of childhood,1 is defined by arthritis lasting greater than 6 weeks clinically beginning in a child before their 16th birthday after infection or other systemic etiologies have been ruled out. JIA is divided into 7 phenotypic subtypes which include: oligoarticular (persistent, extended), polyarticular (rheumatoid factor [RF] positive), polyarticular (RF negative), systemic onset, psoriatic, enthesitis related, and undifferentiated.2
JIA occurs worldwide.
The prevalence is ~1 per 1,000 children, and the incidence is ~12 new cases per 100,000 children.3
JIA appears to occur more commonly in children of Northern European ancestry.
A striking age of onset peak in the oligoarticular type is noted between 1 to 2 years of age, in contrast to polyarticular JIA, which has a biphasic clinical onset with one peak between 1 to 3 years of age and another late in school age and into adolescence. Systemic onset JIA is more common in toddler-aged children, but otherwise onset is rather equally distributed amongst ages.
In general, girls are affected more often than boys, but gender distribution varies with disease subtypes. The most common subtype, oligoJIA, occurs most commonly in toddler-aged girls (F: M, 3:1) and accounts for close to half of JIA diagnoses.
Anterior nongranulomatous uveitis occurs in ~15 percent of ANA-positive patients with either the oligoJIA or RF-negative polyarticular subtype (Figure 172-2).
The etiology of JIA is related to both genetic and environment factors.
Synovitis describes synovial hypertrophy and a proliferation of inflammatory pannus (abnormal fibrovascular tissue). The presence of synovitis is diagnostic in children with JIA. Pannus is composed partially of T and B-lymphocytes as well as macrophages and is accompanied by angiogenesis (Figure 172-3).
Contiguous cartilage and bone may be invaded and damaged.
Cytokines released primarily by proinflammatory macrophages precipitate pannus formation and cartilage/osseus damage.
Genetic factors, aberrant immune responses, and putative environmental triggers play roles in JIA pathogenesis.
Associations of HLA class I and II alleles with JIA are well established, further suggesting the involvement of T cells and antigen presentation in the pathogenesis of JIA.
Hormonal influences may affect pathogenesis given the predominance of females with both oligoJIA and RF-positive polyJIA.
