A histological classification of cutaneous leishmaniasis and its geographical expression

Abstract

A histological comparison has been made of four geographically distinct groups of cutaneous leishmaniasis comprising in all 147 patients. The main finding concerned the relationship between the host tolerance of the parasite, the lysis of macrophages and the damage to connective tissue. It was found (Ridley et al., 1980) that in the Brazilian group, in which parasites were almost undetectable, there was maximal damage to connective tissues. In the central American group, in which amastigotes were apparent in restricted numbers, there was moderate damage to connective tissues apparently associated with lysis of single parasitized macrophages and the liberation of extracellular amastigotes. In the two Old World groups amastigotes were most numerous, macrophage necrosis occurred not singly but in a localized mass, there was no dispersal of extracellular parasites and connective tissue damage was minimal (apart from a few exceptional cases). It was thought that these basic interconnected trends were associated with the toxicity and immunogenicity of the local strains of Leishmania. A five-group histological classification developed for the Brazilian group was applied tentatively to the other three groups of patients, the groups being prefixed to denote that the inflammatory response was cellular (C), fibrinoid (F) or mixed (M). This extended classification served, in conjunction with the parasite index, to encode some of the main characteristics of the global variants of cutaneous leishmaniasis. But although its application pointed to some parallels between the variant forms of the disease the classification needs further clinical evaluation and development.