Cytologic features and frequency of plasmacytoid dendritic cells in the lymph nodes of patients with histiocytic necrotizing lymphadenitis (Kikuchi-Fujimoto disease).

Histiocytic necrotizing lymphadenitis (HNL), also known as Kikuchi-Fujimoto disease, is a benign and self-limiting disease. It is histologically characterized by nodal lesions that show the infiltration of histiocytes, lymphoid cells, myeloid dendritic cells (mDCs), and plasmacytoid dendritic cells (pDCs), along with either apoptotic or karyorrhexic nuclear debris. pDCs have been proposed to be lymphoid early-committed immature DCs which are positive for CD123, CD303, CD68, and HLA-DR but negative for fascin, a mature DC marker, as well as CD13 and CD33,which are mDC markers. In the present study, we analyzed the cytomorphologic features and frequency of pDCs in the lymph nodes of HNL patients. Because the cytologic apprearance of pDCs with Papanicolau staining was quite similar to that of large lymphocytes, immunocytochemistry against CD123 was necessary for the distinction of pDCs. Counting the number of CD123-positive pDCs in the HNL lymph nodes revealed that pDCs more frequently infiltrated the lymph nodes in the setting of HNL than in either reactive lymphadenitis or T and B cell lymphoma. In addition, interestingly, the numberof pDCs did not depend on the age of the HNL lesion, thus suggesting that pDCs are excellent indicators for the cytologic diagnosis of HNL.