Comparison of plasma cell type of Castleman's disease and IgG4-related sclerosing disease: a histopathological and immunohistochemical study.

OBJECTIVES Castleman's disease (CD) is a group of rare atypical lymphoproliferative disorders classified as hyaline vascular (HV) and plasma cell (PC) types. CD may be closely mimicked by IgG4-related sclerosing disease (IgG4-SD) involving the lymph nodes. We retrospectively analyzed findings in patients with CD to elucidate the relationship between CD and IgG4-SD. METHODS Clinicopathological and immunophenotypical characteristics, including IgG+ and IgG4 expression by plasma cells, were analyzed in 87 consecutive patients diagnosed with CD from 1999 to 2010 at two major Korean hospitals. RESULTS The numbers of IgG+ (p < 0.001) and IgG4+ (p < 0.001) cells and the IgG4:IgG ratio (p = 0.003) were significantly higher in the PC than in the HV group. The mean IgG4+:IgG+ plasma cell ratio in the PC group was 25.1%, with 10 patients having a ratio >40%, the threshold IgG4:IgG ratio in patients with IgG4-SD. CONCLUSIONS Patients with the PC form of CD and IgG4-related lymphadenopathy share some features, including the pattern of plasma cell distribution and high-level infiltration of IgG4+ cells. Some patients thought to have the PC form of CD could be reclassified as showing IgG4-related lymphadenopathy.