Indeterminate cell histiocytosis: a rare histiocytic disorder.

A 64-year-old woman, otherwise healthy, presented with multiple reddish-brown, slightly yellowish papules on the face and neck, which had developed 3 years earlier. The lesions were painless and nonpruritic and varied in diameter from 1 to 5 mm. Histological and immunohistochemical examination of cutaneous biopsies revealed a diffuse dermal infiltrate composed mainly of histiocytes which expressed both Langerhans cell as well as monocytic/macrophages cell marker characteristics. Electron microscopic studies revealed no Birbeck granules within the cytoplasm of the neoplastic cells, leading to a diagnosis of indeterminate cell histiocytosis. Indeterminate cell histiocytosis is a very rare disease characterized by the proliferation of indeterminate histiocytes which morphologically and immunophenotypically resemble Langerhans cells but lack Birbeck granules.