S3620 Extranodal Rosai-Dorfman Disease With Pancreatic Involvement

Introduction: Rosai-Dorfman disease (RDD) is a rare histiocytic disorder typically presenting with cervical lymphadenopathy. Extranodal involvement occurs in 40% of cases, with pancreatic involvement being extremely rare. The etiology remains unclear, though immune dysfunction and viral infections have been suggested as triggers. We present a case of extranodal RDD with pancreatic involvement discovered during anemia workup, confirmed through characteristic histopathological findings of emperipolesis and S100-positive histiocytes. Case Description/Methods: A 66-year-old woman presented initially with alternating bowel habits and microcytic anemia. Due to persistent microcytosis, a computed tomography was performed in October 2020, revealing an infiltrative soft tissue mass in the pancreatic tail with splenic vein narrowing, right inguinal lymphadenopathy, and symmetric paraspinal masses suggestive of extramedullary hematopoiesis. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) of the pancreatic mass showed macrophages with emperipolesis, suspicious for extranodal RDD. The patient was referred to hematology for further evaluation. Laboratory evaluation revealed iron 37 mcg/dL (50-175), iron binding capacity 228 mcg/mL (250-450), hemoglobin 12.4 gm/dL, MCV 70 fL, absolute lymphocytes 0.72 × 10(3)/mcL, ESR 38 mm/hr, CRP 19.5 mg/L, positive ANA (1:640), elevated anti-dsDNA, positive SSA/SSB and Smith antibodies. PET-computed tomography showed FDG-avid disease in the pancreatic tail/splenic hilum, lymph nodes, and paraspinal regions. Left cervical node excision demonstrated S100-positive histiocytes with emperipolesis, confirming RDD. Following diagnosis, given the absence of symptoms and clinical stability, a conservative management approach was chosen. The patient has remained clinically stable since diagnosis with continued observation. Discussion: Pancreatic involvement is an exceedingly rare manifestation of RDD, with only a handful of cases reported in the literature. The diagnosis was established through the characteristic finding of emperipolesis in combination with S100-positive histiocytes, demonstrating the importance of adequate tissue sampling and immunohistochemical analysis. Our case illustrates the multisystem nature of RDD and value of systematic evaluation in rare disorders.