Overview
Castleman disease (CD) describes a group of at least 4 disorders that share a spectrum of characteristic histopathological features but have a wide range of etiologies, presentations, treatments, and outcomes. CD was first described in the 1950s by Benjamin Castleman as localized mediastinal lymph node enlargement characterized by increased numbers of lymphoid follicles with germinal center involution and marked capillary proliferation, including follicular and interfollicular endothelial hyperplasia.1 In 1969, Flendrig described the plasma cell (PC), the hyalinized, and the “intermediate” (or mixed) histopathological variants.2,3 Further descriptions over the years provided insight into clinicopathologic associations.3,4 By the mid-1980s, CD was divided into unicentric CD (UCD), which involved a single enlarged lymph node or region of lymph nodes, and multicentric CD (MCD), which involved multiple lymph node stations.5,6 Investigators also noted an association between HIV and MCD.7,8 Co-occurrence with and overlap between the PC neoplasm polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, skin changes (POEMS) syndrome (also known as Takatsuki or Crow-Fukase) and MCD was also noted in the 1980s and 1990s; later, the monoclonal PCs causing POEMS were proposed to be causing the MCD in these cases. Human herpes virus-8 (HHV8) was identified as the etiological driver of all HIV+ and some HIV− MCD cases in the 1990s. In the 2010s, Takai et al recognized a severe form of HHV8− or idiopathic MCD (iMCD) in which patients had a homogeneous constellation of abnormal laboratory tests and clinical features that he called thrombocytopenia, ascites, reticulin fibrosis, renal dysfunction, organomegaly (TAFRO) syndrome.9,10 Recently, the Castleman Disease Collaborative Network (CDCN) proposed a classification system retaining the UCD vs MCD nomenclature, but further dividing MCD by etiological driver (HHV8-associated MCD [HHV8-MCD]; POEMS-associated MCD [POEMS-MCD]; iMCD) and within iMCD by phenotype, iMCD-TAFRO, and iMCD–not otherwise specified