Advanced Practice Rheum: Still's Disease and Fever Save

Know-it-now:

• Still’s disease required diagnostic triad is non-negotiable: 1) quotidian daily spiking fevers (>39°C), 2) an evanescent salmon-pink rash, and 3) markedly elevated inflammatory markers (CRP or ESR).
• Formal diagnostic criteria must be applied (see StillsNow.com).
• The current clinical phenotype (systemic vs. articular disease) determines therapy.
• Macrophage Activation Syndrome (MAS) is the primary life-threatening complication.
• First line therapy in active systemic Still’s disease is either an IL-1 or IL-6 inhibitor. 

Still's disease - a recently unified term, encompassing both systemic juvenile idiopathic arthritis and adult-onset Still's disease - is a systemic autoinflammatory disorder primarily affecting children but occurring in adults up to age 35. Diagnosis after age 50 should be viewed with suspect. The condition is defined by a classic triad of quotidian spiking fevers (>39°C), an evanescent salmon-pink maculopapular rash on the trunk and extremities, and polyarthritis, accompanied by markedly elevated inflammatory markers, leukocytosis with left shift, and universal seronegativity. Diagnosis is clinical and criteria-based — using the Yamaguchi, Cush, or EULAR criteria (see StillsNow.com). Clinicians should resist diagnostic reliance on hyperferritinemia alone, as ferritin >10,000 is seen in only 10–20% of patients and is nonspecific.  A critical clinical distinction must be made between the systemic inflammatory phenotype and the articular phenotype, the latter of which can evolve into a severe erosive polyarthritis requiring RA-level management. The most feared complication is macrophage activation syndrome (MAS), which carries a 20–40% mortality risk. It is heralded by a clinical turn for the worse, soaring LFTs, ferritin >10,000, and a paradoxical shift from leukocytosis to cytopenias. Treatment follows ACR and EULAR 2023 guidelines, emphasizing early initiation of IL-1 or IL-6 inhibitors alongside corticosteroids. MAS can be aggressively treated with emapalumab, calcineurin inhibitors, or JAK inhibitors. Still’s disease complicated by MAS or lung disease warrants referral to specialized centers or experienced pediatric rheumatologists.