Previously known as Still's disease this form of childhood arthropathy carries the most adverse prognosis, with a significant mortality (up to10% in studies prior to aggressive immunomodulatory therapies) (12). The adult version of this disease still carries the label of "adult Still's disease," despite the changes in terminology in the pediatric form. It is unusual for patients to present over the age of 35 years. The latter is similar in presentation, drug responsiveness, and increased amyloidosis risk, but much rarer than the juvenile form affecting 0.16 per 100,000 (13).
Adult and pediatric disease are characterized by a daily spiking fever and an evanescent, non-fixed, macular erythematous rash that is most pronounced at the height of fever and arthritis. If arthritis is not present (as may be the case in early disease), the diagnosis may still be made in the presence of organ involvement, such as serositis (pericarditis or pleurisy), generalized lymphadenopathy, splenomegaly, or hepatomegaly. These features, coupled with a neutrophilia (greater than 13 x 109/L in 75% or more of patients) and elevated acute-phase reactants, may suggest infection, particularly if the arthropathy is not evident at disease onset with systemic features. Specific diseases in addition also require consideration and exclusion (Table 2).
The mean duration of active disease is five years, although a minority of juvenile patients have persistent disease into adult life. This is in contrast
Table 2 Differential Diagnoses Requiring Exclusion in Systemic Onset JIA Infection
Malignancy (particularly neuroblastoma and leukemia) Neonatal onset multisystem inflammatory diseases
FAPA syndrome (fever, aphthous ulceration, pharyngitis, and adenopathy) Hyper IgD syndrome
Periodic syndromes (familial Mediterranean fever, TRAPS, etc.) Kawasaki disease Drug hypersensitivity to adult-onset Still's disease where only 25% to 5% of patients achieve remission in their disease course (14,15). In some patients the systemic features, including the fever and malaise, respond well to nonsteroidal antiinflammatory drugs. In most patients, particularly those with persistent polyarticular arthritis and severe systemic features (such as serositis), cor-ticosteroids and disease modifying drugs may be necessary. The established practice has become the early use of low-dose methotrexate (0.3-0.5 mg/kg/ week, orally or ideally, subcutaneously) administered weekly, since most other disease modifying antirheumatic drugs (gold, sulphasalazine, etc.) have not been shown to be of proven benefit. In the past, AA amyloidosis was relatively common (7-11%) (16) in this subtype but is decreasing in frequency probably due to improved therapies, especially when commenced early. The use of chlorambucil has dramatically improved the outcome of amyloidosis, but in view of its potential toxicity, particularly neoplasia in the longer term, anti-TNF therapy is becoming the preferred therapeutic option (17,18). The systemic onset subset of JIA appears to be the least responsive subset to treatment with etanercept; systemic features, rather than joint inflammation appear to be particularly unresponsive. In systemic JIA there also appears to be a progressive loss of efficacy of etanercept with long term use (17).
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