Pathophys:(J Rheum 1990;21[suppl 21]:1)
Incidence = 1.4/10 000 children/yr; prevalence = 1/1000 children in US
Sx/Si:
Polyarticular type (45%): onset at later age, occasionally rheumatoid factor positive; arthritis in 
5 joints; no systemic sx or si
Pauciarticular type (30%); arthritis in <4 joints; often ANA positive; iridocyclitis leads to blindness often even when arthritis is inactive; eye disease often asx (Clin Exp Rheum 1990;8:499)
Systemic type (25%): intermittent fever <39.4°C (103°F), no arthritis; Still’s disease variant: diurnal fevers, salmon-colored reticular rash, high ESR, pleuropericarditis, but rare or late arthritis
20% still impaired at 10 yr
Growth impairment (Clin Orthop 1990;259:46)
r/o, if age appropriate (Rheum Rev 1991;1:13): juvenile ankylosing spondylitis with positive HLA B27 (Bull Rheum Dis 1987;37[1]:1); child abuse; neoplasms; infections (viral, endocarditis, Lyme disease); granulomatous disorders (Crohn’s, sarcoid); connective tissue diseases like PAN, SS, giant cell arteritis, rheumatic fever, and SLE
Lab:
No good diagnostic test
Hem:Anemia and leukocytosis
Serol:ANA often positive in pauciarticular type. HLA studies 90% positive for B27, cf Reiter’s and ankylosing spondylitis (juvenile type only)
Rx:
(Clin Orthop 1990;259:60)
Physical therapy (Rheum Dis Clin N Am 1991;17:1001)
NSAIDs like ibuprofen; intra-articular steroids; these are enough in 50-60%, esp the pauciarticular type
Methotrexate up to 1 mg/kg/wk, usually 0.5 mg/kg/wk up to 25 mg, better than leflunomide (Nejm 2005;352:1655)
Tumor necrosis factor antagonists (Disease Modifying Antirheumatic Drugs (DMARD)) like adalimumab (Humira) IgG1 recombinant monoclonal antibody to TNF; 20-40 mg IM q2weeks based on weight. OK to continue aminosalicylates, corticosteroids, and/or immunomodulatory agents.