ABSTRACT
<p><b>OBJECTIVE</b>To study the diagnosis and differential diagnosis of histiocytic necrotizing lymphadenitis (Kikuchi disease, KD).</p><p><b>METHODS</b>Histologic analysis and immunohistochemical study (EnVision method) was carried out in 46 cases of KD, 5 cases of nonspecific lymphadenitis (NLD), 5 cases of non-Hodgkin's lymphoma (NHL), 5 cases of Hodgkin's lymphoma (HD), 5 cases of cat-scratch disease (CSD) and 5 cases of tuberculous lymphadenitis (TBL). Electron microscopy was also performed in 6 cases of KD and 2 cases of NHL.</p><p><b>RESULTS</b>Three histologic (proliferative, necrotizing and xanthomatous) patterns were noted in KD. In any of these patterns, there were some basic histologic findings: a wedge-shaped pale area at the edge of the lymph node or paracortical nodules associated with an increase in apoptotic cells or karyorrhectic debris, crescentic histiocytes, proliferative mononuclear histiocytes and absence of or very scanty neutrophils. Immunohistochemical study demonstrated focal occurrence of histiocytes expressing both CD68 and MPO. Electron microscopy confirmed the presence of apoptotic bodies, proliferative mononuclear histiocytes, crescentic histiocytes and dispersed T cells in the lesional areas.</p><p><b>CONCLUSIONS</b>In general, there should not be much difficulty in differentiating KD from other types of lymphadenopathy. Sometimes, problems arise mainly because of the diversity of KD histology. Correct diagnosis can be made if one pays attention to the described characteristic morphology, peculiar immunophenotype of the histiocytes and possibly ultrastructural features.</p>