The lesions sometimes spread up the lymphatic vessels of the arms or legs or extend locally and involve mucous membranes. Often, the infection metastasizes to the nasal or oral mucosa after an intervening period of months to years. Metastatic lesions can erode the nasal septum or the hard palate or soft palate. Some patients may die of malnutrition or bacterial infection. Diffuse cutaneous leishmaniasis occurs in parts of Ethiopia, Venezuela, Brazil, and the Dominican Republic.
Leishmanial organisms abound in the lesions.
Patients with this form of leishmaniasis have a deficiency of cell-mediated immunity, which is similar to the defective immunity that occurs in patients with lepromatous leprosy. Alternatively, the diagnosis can be made by culturing amastigotes on NNN medium inoculated with lesion material. Use of DNA probes based on parasite kinetoplast DNA has allowed detection of organisms that might be missed on histologic section or culturing. Moreover, this technique serves as a rapid method for speciating L. mexicana and L. viannia . In contrast to L. tropica and L. mexicana amastigotes, which can be readily cultured and are abundant in lesions, L. viannia amastigotes are difficult to culture and are sparse in lesions, especially those of mucocutaneous leishmaniasis.