Histopathology of the localized form of cutaneous leishmaniasis due to Leishmania (Leishmania) amazonensis

The microscopic changes found in the localized form of the human cutaneous leishmaniasis due to Leishmania (Leishmania) amazonensis are reported. In this form, less known than the diffuse one caused by the same species, the clinical manifestations are identical to those produced by other Leishmania species of the subgenus Viannia. There is, however, in the localized infection by L (L.) amazonensis, a peculiar feature, only recently discovered: about 50% of the affected individuals are Montenegro-negatives. The main histologic change observed in the skin sections was the presence of groups of macrophages with a large vacuole in the cytoplasm, containing many amastigotes. The microscopic picture is similar to that found in the diffuse form of the disease, the difference being only quantitative. When in large numbers, the macrophages suffers necrosis, which generally starts at the center of the groups. First, in this process, the membrane of the parasitized cells ruptures, and the amastigotes become free; later, both cells and parasites are destroyed. The picture can be seen either in Montenegro-negative or in Montenegro-positive patients. The macrophages with amastigotes may persist in tissues for as long as 6-7 months, while in the infections due to L (V.) braziliensis the parasites usually disappear in a few weeks.