SummaryIdiopathic multicentric Castleman disease (iMCD) is subclassified into iMCD‐thrombocytopenia, anasarca, reticulin fibrosis, renal dysfunction, organomegaly (TAFRO) and iMCD‐not otherwise specified (NOS) according to the Castleman Disease Collaborative Network (CDCN) consensus criteria. With a deeper understanding of iMCD, a group of patients with iMCD‐NOS characterised by polyclonal hypergammaglobulinaemia, plasmacytic/mixed‐type lymph node histopathology and thrombocytosis has attracted attention. This group of patients has been previously described as having idiopathic plasmacytic lymphadenopathy (IPL). Whether these patients should be excluded from the current classification system lacks sufficient evidence. This retrospective analysis of 228 patients with iMCD‐NOS identified 103 (45.2%) patients with iMCD‐IPL. The clinical features and outcomes of patients with iMCD‐IPL and iMCD‐NOS without IPL were compared. Patients with iMCD‐IPL showed a significantly higher inflammatory state but longer overall survival. No significant difference in overall survival was observed between severe and non‐severe patients in the iMCD‐IPL group according to the CDCN severity classification. Compared with lymphoma‐like treatments, multiple myeloma‐like and IL‐6‐blocking treatment approaches in the iMCD‐IPL group resulted in significantly higher response rates and longer time to the next treatment. These findings highlight the particularities of iMCD‐IPL and suggest that it should be considered a new subtype of iMCD‐NOS.