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JIA is a term that encompasses all forms of arthritis that begin before the age of 16 years, persist for more than 6 weeks, and have no identifiable cause. It is the most common chronic rheumatic disease in childhood. The International League of Associations for Rheumatology (ILAR) classification system includes seven disease categories based on the features present in the first 6 months of illness (Table 110-5).15–18 The underlying cause of JIA remains unclear but it appears to be a multifactorial immunopathogenic process in genetically susceptible individuals.15
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Arthritis is the common feature in all types of JIA that results in pain, loss of function and morning stiffness. Joint distribution and systemic symptoms vary based on the type of JIA.
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Polyarticular disease involves five or more joints. It is further categorized as rheumatoid factor-positive (RF[+]) or rheumatoid factor-negative (RF[−]) with RF[−] polyarthritis having at least three distinct subsets. RF[+] polyarthritis includes the presence of IgM rheumatoid factor on at least two occasions, at least 3 months apart. RF[+] polyarthritis is the same as adult RF[+] polyarthritis and is mainly seen in adolescent female patients. At presentation, small joints of the hands and feet tend to be affected; if large joints are affected, it is usually in association with small joint disease. Many patients have involvement of the axial skeleton including the cervical spine; severe cases can result in atlantoaxial instability. Some patients have involvement of the cricoarytenoid joint, where it can result in hoarseness of the voice. The temporomandibular joint may also be affected. Boutonniere deformities (proximal interphalangeal joint flexion and distal interphalangeal joint hyperextension) and swan-neck deformities (proximal interphalangeal joint hyperextension and distal interphalangeal joint flexion) are common. Extra-articular manifestations include rheumatoid nodules in approximately 30% of patients and, much less frequently, aortic regurgitation.
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RF[−] polyarthritis has a biphasic age of onset with an early peak between 2 and 4 years and a late peak between 6 and 12 years. Subsets include an early onset asymmetric arthritis that is associated with positive anti-nuclear antibodies (ANA), an increased risk of iridocyclitis, and a strong HLA association; a polyarthritis that presents in school-age children with symmetric large and small joint disease, an increased ESR, and a negative ANA; and a “dry synovitis” that is characterized by negligible joint swelling with significant joint stiffness, flexion contractures, and a normal or minimally elevated ESR.
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In RF[+] and RF[−] polyarthritis, affected joints are swollen and warm, with minimal or no erythema. Although there is discomfort on range of motion, joint pain is generally not severe. Systemic involvement in polyarticular disease includes fever, irritability, and occasional hepatomegaly. In severe cases, significant growth disturbances can occur. RF[+] polyarticular disease is characterized by progressive, diffuse joint involvement with early radiographic changes, especially in the hands and feet. RF[−] polyarticular disease has a variable outcome depending on its subtype.
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Oligoarticular arthritis involves four or fewer joints during the first 6 months of disease. In the ILAR criteria, patients are excluded from this category if they have psoriasis, a family history of psoriasis and HLA B27-associated illness in a first-degree relative, a positive RF test or if the disease occurs in a male patient older than 6 years. Knees are most commonly affected followed by the ankles, wrists, and elbows. Acute phase reactants may be normal or moderately increased; infrequently ESR is very high. Patients with oligoarticular arthritis are frequently ANA positive (70%–80%), may develop an asymptomatic iridocyclitis (30%), and have a strong association with some HLA alleles.15 Systemic manifestations of disease are generally mild. Patients may have persistent oligoarthritis in which the disease remains confined to four or fewer joints, or they may develop an extended oligoarthritis in which more than four joints become involved after the first 6 months. Risk factors for the development of extended oligoarthritis include ankle, wrist, or hand involvement, symmetric arthritis, arthritis of two to four joints and an elevated ANA titer and ESR.16
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Systemic onset disease occurs throughout childhood. Diagnosis of systemic arthritis requires the presence of arthritis accompanied or preceded by at least 2 weeks of quotidian fever plus typical evanescent rash (discrete, circumcised, salmon-colored, 2- to 10-mm macules on the trunk and proximal extremities that typically coincide with fever), hepatomegaly, splenomegaly, generalized lymphadenopathy, or serositis. The onset of joint disease may be significantly delayed, which can obscure the diagnosis of JIA. Patients may be ill-appearing and have myalgias and abdominal pain during episodes of fever. Laboratory findings include leukocytosis with a preponderance of neutrophils, elevated liver enzymes, microcytic anemia, thrombocytosis, and very high ESR and CRP concentrations. The ANA titer is rarely positive.15 In approximately 50% of cases, systemic-onset JIA is associated with a relapsing-remitting course in which arthritis accompanies episodes of fever and remits when systemic features are controlled. In the other 50% of patients, it is associated with an unremitting, debilitating arthritis with few systemic symptoms. Other complications include the development of pericarditis, which in some cases can result in a clinically significant pericardial effusion, myocarditis, or pleuritis. Very infrequently, patients develop amyloidosis.
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A rare but life-threatening complication of systemic JIA is macrophage activation syndrome. This is characterized by the sudden onset of sustained fever, pancytopenia, hepatosplenomegaly, liver insufficiency, coagulopathy, and neurologic symptoms. Pancytopenia, prolonged prothrombin and PTTs, elevated fibrin split products, hypertriglyceridemia, hyponatremia, and increased ferritin concentrations are present. The ESR is often low.
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The differential diagnosis of JIA includes ARF, SLE, bacterial arthritis, reactive arthritis, and neoplastic diseases, especially leukemia. In the ED, the workup of suspected JIA includes a complete blood count, renal function studies, and a rapid streptococcal screening. Tests for ANAs and rheumatoid factors are indicated even though results are not immediately available. If a pyogenic arthritis is suspected, analysis of joint fluid is indicated. Patients with systemic-onset disease with evidence of myocarditis or pericarditis require an electrocardiogram and echocardiogram. Consultation with a pediatric rheumatologist is recommended and hospitalization (especially with systemic onset disease) may be necessary.
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Although JIA tends to be a chronic illness, there has been great improvement in functional outcome over the past decade. Indicators of poor outcome include greater severity or extension of arthritis at onset, symmetrical disease, early wrist or hip involvement, presence of RF, persistent active disease, and early radiographic changes.19
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The treatment of JIA consists of physical and occupational therapy to maintain and improve range of motion, muscle strength, and skills for daily activities. Splints may be used to prevent contractures. Aggressive treatment with NSAIDs is the initial treatment for most patients with JIA. For pauciarticular disease, intra-articular steroids may be used. For cases that do not respond to NSAIDs, glucocorticoids, cytotoxic drugs, or biological medications may be effective.20,21 Sulfasalazine is effective in patients with extended oligoarticular JIA and juvenile spondyloarthropathies. Pericarditis or myocarditis may respond to therapy with prednisone.20,21 Macrophage activation syndrome is treated with high-dose steroids and cyclosporin.