First-Line Treatment for Polyarticular Juvenile Idiopathic Arthritis
Methotrexate (MTX) is the first-line disease-modifying antirheumatic drug (DMARD) for this 10-year-old with polyarticular juvenile idiopathic arthritis (JIA), positive rheumatoid factor, fever, and small joint stiffness. 1
Rationale for Methotrexate as First-Line Therapy
The 2019 ACR/Arthritis Foundation guidelines for juvenile idiopathic arthritis strongly recommend methotrexate over leflunomide or sulfasalazine as the initial DMARD for children with polyarticular JIA. 1
This patient has poor prognostic factors including positive rheumatoid factor (RF 100, normal <58), which places them at higher risk for joint damage and mandates aggressive disease-modifying therapy from diagnosis. 1
Methotrexate should be initiated at 10 mg/m² weekly for polyarticular-course JIA, with subcutaneous administration conditionally recommended over oral methotrexate to optimize absorption and reduce gastrointestinal side effects. 1, 2
Therapeutic response typically begins within 3-6 weeks, with continued improvement for another 12 weeks or more; the maximal dose should be maintained for at least 3 months before assessing efficacy. 2
Role of NSAIDs and Corticosteroids
NSAIDs are conditionally recommended only as adjunct therapy, not as monotherapy, because they provide symptomatic relief without disease modification or prevention of joint damage. 1
Corticosteroids alone do not prevent radiographic progression and are not disease-modifying therapy. 3
Bridging therapy with a limited course of oral glucocorticoid (<3 months) during initiation of methotrexate is conditionally recommended in patients with high or moderate disease activity, particularly when there is limited mobility or significant symptoms. 1
However, chronic low-dose glucocorticoid therapy is strongly recommended against in children with JIA due to growth suppression, osteoporosis, and other long-term toxicities. 1
Treatment Targets and Monitoring
The treatment goal is clinical inactive disease or remission, assessed using the clinical Juvenile Disease Activity Score based on 10 joints (cJADAS-10). 1
Disease activity should be monitored every 1-3 months, with therapy adjusted if there is no improvement by 3 months or the target is not reached by 6 months. 3
If methotrexate monotherapy fails after an adequate trial (3-6 months at optimal dose), escalation to biologic DMARDs (TNF inhibitors, tocilizumab, or abatacept) in combination with methotrexate is recommended for patients with poor prognostic factors. 1
Critical Pitfalls to Avoid
Delaying DMARD initiation leads to irreversible joint damage—treatment must begin immediately upon diagnosis. 3, 4
Using NSAIDs or corticosteroids alone provides only symptomatic relief without disease modification, allowing unchecked progression of joint destruction. 3, 5
Undertreating patients with poor prognostic factors (such as positive RF and polyarticular disease) by relying on NSAIDs or low-dose corticosteroids alone will result in worse long-term outcomes. 3
Subcutaneous methotrexate should be considered early if oral administration is poorly tolerated or ineffective, as children receiving 20-30 mg/m²/week may have better absorption with parenteral administration. 1