Oligoarticular arthritis, meaning synovitis involving four or fewer joints, is the most common subtype of JIA and accounts for approximately half of all cases Oligoarticular arthritis occurs more often in young girls, typically causing swelling, pain, and limitation of movement in one or more large joints ANAs are detectable in the sera of many of these children, and their presence at any titer correlates with a higher risk for developing iridocyclitis Polyarticular arthritis (both RF-positive and RF-negative) occurs more commonly in girls It is characterized by the insidious onset of symmetric synovitis in five or more joints with associated morning stiffness and disability Both large and small joints ( Fig 101.6 ) may be involved The presence of RF and/or anti-CCP antibodies corresponds to an increased risk of severe, erosive arthritis, much like adult rheumatoid arthritis RF positivity is also associated with the development of vasculitic complications and subcutaneous nodules Cervical spine involvement occurs in approximately 30% to 50% of patients with polyarticular JIA, resulting in neck pain, stiffness, and torticollis Unlike oligoarticular JIA, in which ocular involvement is the cause of the most significant morbidity, polyarticular disease may result in severe musculoskeletal disability Thus, involvement of the temporomandibular joint may result in restricted ability to open the mouth, involvement of the hips may permanently affect ambulation, and small joint arthritis of the hands may compromise manual dexterity The least common subtype of JIA is systemic JIA formerly known as Still disease, which is conceptualized as an autoinflammatory, rather than autoimmune condition, and is distinguished by its systemic features This subtype occurs most often in boys younger than years of age, although it has been reported even in adults Clinically, these children often present with unremitting fevers; they may have high spiking temperatures (39° to 41°C) for several weeks or months, classically in a twice daily pattern Although the child often feels stiff and does not move normally, arthritis may not be a prominent feature at the onset of the disease Diagnosis, therefore, generally involves excluding infectious and malignant conditions that cause fever and systemic inflammation, especially sepsis, leukemia, and neuroblastoma A characteristic salmonpink evanescent maculopapular rash ( Fig 101.7 ), diffuse lymphadenopathy, and hepatosplenomegaly (HSM) may also be present in the early stages, offering clues to the diagnosis Arthralgias and myalgias are common, and pericarditis and other serositis occur most typically in this subtype of JIA With time, systemic features of the disease become less prominent, and polyarticular arthritis becomes the major focus of management Systemic JIA is associated with considerable morbidity, including the potentially life-threatening complication of MAS which is discussed in greater detail below