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Histiocytosis X
(Langerhans Histiocytosis)
Histiocytosis X clearly qualifies as a borderline lesion. It has the qualities of a neoplastic process, but some localized examples may spontaneously regress. It is characterized by
distinctive cytologic features with the nuclear changes being most characteristic; many of the nuclei are deeply grooved. In the skin the infiltrates often are best developed at the interface between the papillary
dermis and the reticular dermis. Some of the cells may infiltrate the epidermis. Lymphocytes, plasma cells, and neutrophils may be represented in the infiltrates, but eosinophils usually are distributed among the
histiocytes. In some examples, the histiocytes show some degree of nuclear atypia. Acute, chronic disseminated, and chronic localized variants are recognized; these variants are defined more on clinical staging than
histologic features. Clinico-pathologic variants include Letterer-Siwe disease, Hand-Schuller-Christian disease, and eosinophilic granuloma. The histiocytes of histiocytosis X share with Langerhans cells the
antigens S100 protein and CD1a. It would, however, be a mistake to attribute to Langerhans any portion of our understanding of histiocytosis X. If attribution is required, then Lichenstein should be cited.
Atypical Histiocytosis X
Atypical histiocytosis X is characterized by a significant degree of cytologic atypia. In addition, the lesions may behave in a locally aggressive fashion. They may involve regional
lymph nodes and soft tissue. The latter features are not unique to the category of atypical histiocytosis X, but a pathologist’s interpretation of clinical sequences is likely to be strongly colored if, on a
histologic section, an infiltrate shows cytologic atypia.
Itoh H, et al: Primary cutaneous Langerhans cell histiocytosis showing malignant phenotype in an elderly woman: report of a fatal case. J Cutan Pathol 2001; 28: 371-8.
Congenital Regressing Histiocytosis
Classic histiocytosis X is uncommon as a congenital disorder. On the other hand, there is a category of congenital histiocytic lesions in which the infiltrates share cytologic and
immunologic features with the cells of histiocytosis X; this variant is congenital regressing histiocytosis. The lesions tend to be prominently perivascular and may irregularly involve the reticular dermis. They may
extend to the dermal-epidermal interface and may show a central area of necrosis or degeneration.
Rosai-Dorfman Disease
(Sinus Histiocytosis with Massive Lymphadenopathy)
Sinus Histiocytosis with massive lymphadenopathy is a disorder characterized by infiltrates of inflammatory cells (including lymphocytes, plasma cells, and neutrophils) and by cords and clusters of distinctive
histiocytes. The histiocytes have an abundant amount of pale cytoplasm and plump, round nuclei with marginated chromatin. In addition, nucleoli are large and acidophilic. The distinctive histiocytes often contain
inflammatory cells, including neutrophils and lymphocytes, in their cytoplasm (emperipolesis). The lymphocytes in the cytoplasm of the histiocytes may be outlined by a clear halo. The infiltrates of histiocytes in
lymph nodes are predominantly sinusoidal in distribution. In nodal lesions of sinus histiocytosis with massive lymphadenopathy, the lymphadenopathy may be massive, hence the alternate designation. In addition to
lymph nodes, soft tissue, and skin, the infiltrates may involve the viscera.
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