A case of histiocytic necrotizing lymphadenitis with bone marrow and skin involvement.

We report a case of histiocytic necrotizing lymphadenitis (HNL) with bone marrow extension in a 29-year-old male in which many large mononuclear cells infiltrated the bone marrow and mimicked malignant lymphoma. A lymph node biopsy confirmed the diagnosis of HNL. Immunohistologically, the infiltrating cells in the bone marrow were positive for lysozyme, LeuM1, Kp-1 and T-cell markers. The cells did not show haemophagocytosis. A skin biopsy from an accompanying facial skin rash revealed a proliferation of large cells similar to those observed in affected foci of the lymph node in subcutaneous tissue. The infiltrating cells were mainly lysozyme and Kp-1-positive histiocytes, some with phagocytosis of nuclear debris but none characteristic of haemophagocytosis. Transformed T-cells were also infiltrating.