A case of non-selective phagocytosis of hemosiderin and melanin of dermal histiocytes in stasis dermatitis

Abstract

A case study was undertaken to determine whether or not the same dermal histiocytes could phagocytose both melanin and hemosiderin simultaneously. A biopsy specimen was taken from a pigmented lesion of the lower leg of a 57-year-old woman with stasis dermatitis. The specimen was processed for histology, conventional transmission electron microscopy and electron-probe X-ray microanalysis. Histologically, numerous histiocytes with their cytoplasm packed with either Prussian blue-positive granules or Fontana-Masson-positive granules were distributed almost equally in the dermis. Electron microscopically, the dermis had many histiocytes with their cytoplasm containing solitary or compound electron-dense substances. The electron-dense substances were classified into three types according to their degree of electron density. By electron-probe X-ray microanalysis, these electron-dense substances were classified into iron-containing and non-iron-containing substances. Both substances were seen in the cytoplasm of the same histiocytes and even in the same compound electron-dense substance. The former were siderosomes and the latter were probably melanosomes. These results show that the same dermal histiocytes probably phagocytose non-selectively both hemosiderin and melanin granules.