#00064872

A 7-month old male with a history of biliary atresia, status post Kasai procedure, presented with worsening abdominal distension. Laboratory data showed anemia, thrombocytopenia, hypoalbuminemia, hypergammaglobulinemia, and elevated IL-6, CRP, and ESR. Imaging showed extensive abdominal and retroperitoneal lymphadenopathy. Excisional biopsy demonstrated an enlarged lymph node with numerous small, widely spaced follicles with regressed germinal centers, occasionally pierced by vessels (Panel A & B). Interfollicular areas showed prominent vascularity (Panel B), increased CD138+ plasma cells (Panel C), and frequent small-sized TdT+ CD99+ T-cells (Panel D) lacking overt cytologic atypia. Flow cytometry identified a discrete population of immature T-cells expressing dim CD45 (panel E), CD34 (Panel F), CD10 (Panel F), TDT (Panel G), CD1a, CD2, cytoplasmic CD3 (Panel G), CD5, and CD7, and lacking surface CD3, CD4, CD8, and surface TCR. TCR beta polymerase chain reaction studies were negative for clonal rearrangement. A LANA immunostain was negative. The clinicopathologic findings were consistent with idiopathic multicentric Castleman disease (iMCD), HHV-8 negative, with a modest proliferation of immature T-cells.

iMCD is a rare entity characterized by widespread lymphadenopathy, systemic inflammatory symptoms, and multi-organ dysfunction. iMCD is extremely uncommon in children, and whether its underlying pathophysiology differs from that observed in adults remains uncertain. Clinically indolent T-lymphoblastic proliferations (iT-LBP) can be seen in Castleman disease and may occasionally show features that mimic T-cell malignancies. However, iT-LBPs lack significant morphologic atypia, aberrant antigen expression, and monoclonality, and do not involve the bone marrow or mediastinum.