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Systemic Juvenile Idiopathic Arthritis

Systemic Juvenile Idiopathic Arthritis: Pathogenesis and clinical findings Genetic predisposition (eg. HLA-DRB1*11; IL1, IL6, IL10 & MIF polymorphism, others) Unknown environmental trigger (eg. infection, medications, other environmental stimuli) Systemic Juvenile Idiopathic Arthritis (sJIA) A subtype of JIA occurring in children < 16 y.o. that presents with at least 2 weeks of fever (quotidian for ≥3 consecutive days) along with other symptoms (eg. arthritis, evanescent rash, generalized lymphadenopathy, hepatomegaly, splenomegaly, serositis) Author: Eryn Bugbee Reviewers: Taylor Krawec Annie Pham Michelle J. Chen Emily J. Doucette Danielle Nelson* * MD at time of publication Idiopathic innate immune cell activation (eg. via Toll-like receptor (TLR) signaling) Splenomegaly TLR signaling induces innate immune cell activation & proliferation Leukocytosis (>15,000/mm3) with neutrophilia Positive feedback on inflammatory cascade Activated innate immune cells ↑ inflammatory cytokine production Secondary activation & proliferation of lymphocytes Lymphadenopathy ↑ Interleukin-18 ↑ Interleukin-1β ↑ Interleukin-6 ↑ Ferritin production & secretion by macrophages & hepatocytes ↑ Synthesis & activation of proinflammatory S100 proteins in epithelial cells & keratinocytes ↑ Synovial inflammation & hyperplasia Megakaryocyte stimulation in bone marrow ↑ Prostaglandin synthesis in CNS Enzymatic degradation of bone/cartilage ↑↑ Ferritin Evanescent (<24hrs) erythematous rash (hallmark feature) Arthritis in ≥ 1 joint(s) ↑ C-reactive protein & ferritin Thrombocytosis Quotidian fever (reaches ≥39˚C daily & returns to ≤37˚C between fever peaks) Possible environmental trigger (eg. EBV, CMV, influenza) Genetic predisposition (eg. mutations affecting cytolytic functioning to NK cells & CD8+ T cells, others) Sustained pro-inflammatory state & overproduction of cytokines (cytokine storm) Macrophage activation syndrome (characterized by sustained fever & laboratory findings consistent with hyperinflammatory state (eg. hyperferritinemia, coagulopathy, pancytopenia, hepatic dysfunction)) Mechanism Sign/Symptom/Lab Finding Complications Published Nov 2, 2025 on www.thecalgaryguide.com Hepatocyte stimulation in liver Acute phase protein production Hepatomegaly Legend: Pathophysiology