Non-Langerhans cell histiocytosis with isolated CNS involvement: an unusual variant of Erdheim-Chester disease.

Benign histiocytic proliferations are identified by their component cells and classified as either Langerhans cell histiocytosis or non-Langerhans cell histiocytosis. We report a 58-year-old Caucasian woman who presented with diabetes insipidus and was found to harbor a large suprasellar mass. Histopathological analysis was consistent with non-LCH. The differential diagnoses included juvenile xanthogranuloma, adult-onset xanthogranuloma, xanthoma disseminatum, Rosai-Dorfman disease, and Erdheim-Chester disease. Immunohistochemical examination demonstrated a proliferation of large lipid-laden histiocytic cells which were positive for CD68, negative for S100 protein, and showed only faint, background staining for CD1a. We present a case of an autopsy-confirmed non-Langerhans cell histiocytosis limited to the central nervous system and evaluated with both immunohistochemical and ultrastructural studies. Based on the multifocality, anatomic distribution, and immunostaining features, a diagnosis of Erdheim-Chester disease was made. This is only the second reported case of Erdheim-Chester disease with intracranial involvement but absence of extracerebral manifestations. Given the overlapping clinicopathologic, radiographic, and immunohistochemical profiles, differentiating between these rare histiocytic disorders can often present a significant diagnostic challenge. A systematic approach using all available clinical, laboratory, radiographic, histologic, immunohistochemical and ultrastructural data is essential for proper discrimination between the numerous histiocytoses.