++
++
Non-Langerhans cell histiocytosis (NLCH), or class II histiocytosis, represents a broad group of different disorders characterized by the proliferation of histiocytes other than Langerhans cell (LC) (Table 148-1).
++
++
In some textbooks, these diseases are gathered under the term: macrophage/dermal dendritic cell disorders. In 2001, Zelger et al suggested a unifying approach to understand this disease group. They identified different types of macrophages in the prototype lesion, juvenile xanthogranuloma, and then used this morphology to subcategorize the diseases.
++
Clinicopathologic overlap makes it difficult to place some patients exactly into one defined entity, indicating a close relationship between these disorders. While many of these disorders may feature foamy cells, affected patients are normolipemic. In all instances, the etiology and pathogenesis are unknown.1
++
Most of these cells share the same immunophenotypes, but the resulting disorders differ in clinical presentation and course. Although all NLCH disorders are considered reactive with no clinical evidence of malignancy, some forms, as with class I histiocytosis (Langerhans cell histiocytosis or LCH), can be invasive and therefore they are not necessarily biologically benign. Patients have been described who have developed both LCH and an NLCH, particularly, juvenile xanthogranuloma (JXG).
++
These cases seem to demonstrate a relationship between LCH and NLCH.2 According to some authors the dendritic cell is the presumed cell of origin of both LCH and NLCH, leading to the shared categorization of these diseases as dendritic cell-related disorders and separated from macrophage-related proliferations such as sinus histiocytosis ...