Electromicroscopic study of histoid leprosy with special reference to its histogenesis

Biopsies from 2 patients clinically diagnosed and confirmed by histopathological studies as histoid leprosy were examined using and electronmicroscope. The cells that form the nodule are found to contain far more solid bacilli and much less electron transparent substance than those in lepromatous lesions. They have the characteristics of both macrophages and fibroblasts. It is reasonable to conclude that they are histiocytes produced by local multiplication in response to stimulation by rapidly proliferating M. leprae rather than from accumulation of blood monocytes at the site of inflammation as lepromatous lesions.