A 6-year-old boy presents with 6 weeks of daily fever spiking to 40°C (quotidian pattern, normalizing between spikes), salmon-pink evanescent truncal rash appearing with fever, arthritis of both knees and wrists, and hepatosplenomegaly. Ferritin is 12,000 ng/mL. The diagnosis is systemic JIA (sJIA). The pathological cytokine most elevated in sJIA (differentiating it from other JIA subtypes) that serves as a therapeutic target is:

• A IL-6 (targeted by tocilizumab) ✓
• B TNF-alpha (targeted by etanercept)
• C IL-17A (targeted by secukinumab)
• D IL-12/23 (targeted by ustekinumab)

Explanation

Systemic JIA (sJIA) is driven by autoinflammatory mechanisms with massive IL-6 and IL-1 production from activated macrophages. Extremely elevated ferritin (>10,000 ng/mL) is a cardinal feature, partly driven by IL-6-mediated ferroportin suppression. Tocilizumab (anti-IL-6 receptor monoclonal antibody) and canakinumab (anti-IL-1 beta) are the approved biologic agents for sJIA. IL-6 drives the acute-phase response (fever, ferritin, CRP elevation) and joint destruction in sJIA. TNF-alpha blockers (etanercept) are less effective for sJIA. Macrophage activation syndrome (MAS) is the most feared complication, managed with high-dose steroids and anakinra/ciclosporin.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.