A 4-year-old girl has had fever every day for 4 weeks, a salmon-colored evanescent rash appearing during fever spikes, lymphadenopathy, hepatosplenomegaly, and painful swollen knees and wrists. Ferritin is 12,000 ng/mL. RF is negative, ANA is negative. Which JIA subtype does this represent, and what is the significance of the ferritin level?
- A Polyarticular RF-negative JIA; markedly elevated ferritin indicates active systemic inflammation without specific diagnostic significance
- B Oligoarticular JIA with uveitis; ferritin elevation reflects anemia of chronic disease
- C Systemic JIA (sJIA); ferritin >10,000 ng/mL raises strong concern for macrophage activation syndrome (MAS), a life-threatening complication ✓
- D Enthesitis-related arthritis; ferritin elevation reflects acute phase response to entheseal inflammation
Explanation
Systemic JIA (sJIA, previously Still's disease) is characterized by: quotidian (daily) fever spikes, salmon-colored evanescent rash, lymphadenopathy, hepatosplenomegaly, and arthritis (>6 weeks). Ferritin >10,000 ng/mL (5x upper limit of normal) is a key diagnostic criterion for Macrophage Activation Syndrome (MAS)—the most feared and potentially fatal complication of sJIA—characterized by uncontrolled immune activation, cytopenias, coagulopathy, and multi-organ failure. In sJIA with markedly elevated ferritin, MAS must be urgently excluded. RF-negative polyarticular JIA does not have systemic features; oligoarticular JIA presents with ≤4 joints; ERA affects HLA-B27 positive older boys with enthesitis.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.