Pediatric Idiopathic Multicentric Castleman Disease Is Often Severe But Responsive to Siltuximab.

BACKGROUND: Idiopathic multicentric Castleman disease (iMCD) is a potentially fatal immunologic disorder marked by widespread lymphadenopathy and inflammation. Siltuximab, an interleukin-6 (IL-6) inhibitor, is the only FDA-approved treatment for adult patients with iMCD. Limited data exist on pediatric iMCD or its responsiveness to siltuximab. We hypothesize that pediatric iMCD patients will present and respond similarly to adult patients. PROCEDURE: We queried ACCELERATE, the largest global iMCD registry with expert-confirmed diagnoses. We analyzed two iMCD cohorts: pediatric patients (18 years of age or younger at symptom onset) and adults. We assessed both disease severity, using a modified CHA (C-reactive protein [CRP], hemoglobin, albumin) score, and response to treatment. A response was defined as normalization in greater than 50% of abnormal clinical parameters and was considered durable if no new regimens were started within 1 year of initiating the index regimen. RESULTS: Pediatric iMCD patients (N = 30) had higher CHA scores at diagnosis (1.67 vs. 1.31, p = 0.024) than adult iMCD cases (N = 96), indicating greater disease severity and higher CRP. Pediatric and adult iMCD patients had similar responses to siltuximab ± CS (12/14, 86% vs. 35/48, 73%, p = 0.48) as well as other treatments. CONCLUSIONS: In the largest pediatric iMCD analysis to date, we found more severe disease and similar responses to siltuximab in children compared to adults.