Post-kala-azar dermal leishmaniasis: a light and electron microscopic study of 18 cases.

Post-kala-azar dermal leishmaniasis (PKDL) is caused by the protozoan parasite, Leishmania donovani, and is seen in patients with history of having been treated earlier for the visceral disease form, kala-azar, caused by the same organism. The findings from 18 patients with PKDL are described in this study. The skin manifestations ranged from hypopigmented macules to infiltrated plaques and nodules. Histopathologic examination revealed a cellular infiltrate of lymphocytes, plasma cells, and macrophages. The macrophages were scattered amidst the infiltrate without any localization. In hypopigmented lesions, the infiltrate was confined to the perivascular region in the superficial dermis and was composed mainly of lymphocytes and few plasma cells. In the nodular lesions, the infiltrate occupied the entire thickness of the dermis. Leishman-Donovan bodies were scarce and identified in 16 cases after a prolonged search of Weigert's iron hematoxylin-stained sections. In 2 cases, Leishman-Donovan bodies were not demonstrable. Electronmicroscopic study revealed parasitized macrophages which showed no structural evidence of activation despite the active cellular response around them. The fine structure of the parasites in the histiocytes was also well maintained. This unusual tropical dermatosis is a unique example of change in organotropism of a parasite associated with a change in the host response.