A New Castleman Disease Subtype

Idiopathic plasmacytic lymphadenopathy (IPL) is a rare benign inflammatory disease categorized by proliferation of polyclonal plasma cells in the lymph nodes, causing large amounts of antibody production. Idiopathic multicentric Castleman disease (iMCD) is a unique disease subtype that is unrelated to the unicentric and the HHV-8-associated forms. Historically, iMCD has been classified into two groups: iMCD-TAFRO (thrombocytopenia, anasarca, fever, reticulin fibrosis, and organomegaly) and iMCD-NOS (not otherwise specified).

The jury is still out on whether the aforementioned IPL should belong to the iMCD-NOS group. But a recent paper tackled the topic by examining specimens of the iMCD-NOS group, finding evidence to suggest that IPL should possibly be considered a separate disease subgroup in iMCD (1).

Historically, IPL has been associated with iMCD-NOS because they share similar clinical pathologies. To test the validity of this consensus, the team analyzed lymph node specimens from patients who both qualified for iMCD and were negative for KSHV/HHV8 infection.

The majority of the specimens (34) were classified under the IPL group, with a total of eight others being categorized as the non-IPL group. Histological analysis demonstrated unique pathological characteristics in the IPL group; namely, greater plasmacytosis and hyperplastic germinal centers compared with the non-IPL specimens. Conversely, the vascularity of the non-IPL group was higher than that of the IPL group. Clinically, the IPL group showed notable thrombocytosis and elevated serum IgG levels compared with non-IPL specimens, whereas pleural effusion and ascites were less common in the IPL counterparts. 

The IPL group was also seen to respond better to the anti-IL-6 receptor antibody, whereas the non-IPL specimens needed more intensive medical treatment. According to the researchers, these findings justify IPL forming a unique subgroup of iMCD-NOS, and further molecular analysis is required to find subtype-specific biomarkers to improve patient outcomes.