From Castleman disease histopathological features to idiopathic multicentric Castleman disease: a multiparametric approach to exclude potential iMCD histopathological mimickers.

Aims: International consensus diagnostic criteria for idiopathic multicentric Castleman disease (iMCD) includes lymph node Castleman disease (CD) histopathological features as major criteria. Our aim was to apply those criteria in a series of 42 cases with CD to find differences among unicentric CD, iMCD, HHV-8+multicentric CD (HHV-8+MCD) and POEMS/plasma cell neoplasia (PCN)-associated CD.

Methods: Available clinical and laboratory criteria were collected. Histopathological features (germinal centre hyperplasia/regression, plasmacytosis, hypervascularity and follicular dendritic cell (FDC) prominence) were graded and immunohistochemistry with antibodies against CD20, CD3, CD138, HHV-8, Ig isotype (IgG, IgG4, IgA, IgM, IgD), kappa, lambda was performed in all cases.

Results: Fourteen cases had hyaline-vascular type unicentric CD, 15 were HHV-8+MCD, 7 cases PCN/POEMS-associated CD and 5 cases were iMCD. One case was consistent with systemic lupus erythematosus (SLE) lymphadenopathy. Differences in grading of the CD-associated histopathological features showed that FDC proliferation was prominent in unicentric CD, hypervascularity was increased in HHV-8 positive MCD and germinal centre hyperplasia was restricted to iMCD cases and SLE. Monotypic plasma cells were readily identifiable in the lymph node biopsies in 43% of PCN/POEMS-associated CD. All three cases had lambda light chain restriction with IgA (two cases) and IgG (one case) isotypes.

Conclusions: HHV-8+ MCD and PCN/POEMS-related CD are the major mimickers of iMCD in lymph node biopsies. Grading of the five histopathological features for CD might be useful to, in conjunction with complete ancillary testing, suggest for specific disease entities.