Histochemistry of B663 pigmentation: ceroid-like pigmentation in macrophages.

Histochemical studies were made of pigmented cutaneous lesions from three cases of lepromatous leprosy treated with B663 to determine the nature and histogenesis of the brown pigmentation which develops as a side effect of the drug. One case of DDS-treated leprosy and four cases of untreated leprosy were also investigated histochemically as controls. The brown pigmentation of the skin is due to deposition of a ceroid-like substance in the macrophages, which is a yellowish-brown, acid-fast lipid pigment. It is insoluble in fat solvents and accepts lipid dyes even after lipid extraction by fat solvents. The macrophages in the B663-treated leprosy contain more neutral fat and less phospholipid than the untreated lepromatous leprosy tissues. Ceroid in the macrophages probably originated from unsaturated fatty acids of the leprosy bacilli through oxidation or their binding with the drug. Crystals of the drug were not found in the macrophages in this series, even on the tissues embedded in carbowax or frozen sections.