Atypical histiocytic proliferation with features of histiocytic sarcoma

Abstract

Case report We present a case of an 83-year-old man with axillary lymphadenopathy and PET positive bone-destructive lesions in the sternum and iliac crest. Histology of the lymph node showed a histiocytic proliferation with near-complete effacement of the normal nodal architecture. There was focal spindling of cells with marked nuclear pleomorphism and occasional mitotic figures including abnormal forms. Erythrophagocytosis was apparent. The cells showed strong staining for CD163 and CD4, had patchy staining with S100, and were negative for CD1a, CD20, CD3, CD21, CD23, CD30 and CD45, as well as MPO, HMB45, and AE1/3. Ki-67 stained 1–2% of cells. The bone lesions showed similar features. Discussion The histological differential diagnosis for this histio-cytic proliferation includes Rosai–Dorfman disease (RDD, also known as sinus histiocytosis with massive lymphadenopathy), a rare benign condition with nodal and extranodal involvement, and histiocytic sarcoma (HS), a rare haematopoietic neoplasm. While a proliferation of histiocytes showing emperipolesis is characteristic of RDD, the marked pleomorphism, architectural effacement, relative absence of sinusoidal involvement, and minor S100 staining are unusual for RDD. A diagnosis of atypical histiocytic proliferation was rendered with features favouring HS. This case is presented to raise awareness of these challenging histiocytic lesions and to include HS and RDD in the differential diagnosis of concurrent lymphadenopathy and lytic bone lesions. We present a case of an 83-year-old man with axillary lymphadenopathy and PET positive bone-destructive lesions in the sternum and iliac crest. Histology of the lymph node showed a histiocytic proliferation with near-complete effacement of the normal nodal architecture. There was focal spindling of cells with marked nuclear pleomorphism and occasional mitotic figures including abnormal forms. Erythrophagocytosis was apparent. The cells showed strong staining for CD163 and CD4, had patchy staining with S100, and were negative for CD1a, CD20, CD3, CD21, CD23, CD30 and CD45, as well as MPO, HMB45, and AE1/3. Ki-67 stained 1–2% of cells. The bone lesions showed similar features. The histological differential diagnosis for this histio-cytic proliferation includes Rosai–Dorfman disease (RDD, also known as sinus histiocytosis with massive lymphadenopathy), a rare benign condition with nodal and extranodal involvement, and histiocytic sarcoma (HS), a rare haematopoietic neoplasm. While a proliferation of histiocytes showing emperipolesis is characteristic of RDD, the marked pleomorphism, architectural effacement, relative absence of sinusoidal involvement, and minor S100 staining are unusual for RDD. A diagnosis of atypical histiocytic proliferation was rendered with features favouring HS. This case is presented to raise awareness of these challenging histiocytic lesions and to include HS and RDD in the differential diagnosis of concurrent lymphadenopathy and lytic bone lesions.