Ten years of dapsone in lepromatous leprosy: clinical, bacteriological and histological assessment and the finding of viable leprosy bacilli

Abstract

Twelve lepromatous patients who had completed 10 to 12.5 yr continuous chemotherapy, principally or entirely with dapsone, were assessed clinically, bacteriologically and histologically. In all 12 the disease showed full clinical response to therapy, although 3 patients remained smear positive, and 2 of these still suffered from mild erythema nodosum leprosum. However, by mouse footpad inoculation it was shown that 7 of the 12 patients still harboured viable Myco. leprae. Thus bacterial multiplication was obtained in mice inoculated with 10 of 37 tissue suspensions prepared from extensor skin (4), striated muscle (3), peripheral nerve (2) and smooth muscle (1), although the numbers of positive footpads in each group of mice were small, in keeping with the minute numbers of leprosy bacilli of variable viability inoculated. No bacterial enhancement was obtained in thymectomised irradiated mice, and 3 of 6 strains died out on passage; these findings recalling the difficulties encountered by McCune et al. in culturing Mycobacterium tuberculosis in vitro from tuberculous mice subjected to effective chemotherapy. Three of these strains of Mycobacterium leprae (2 from skin and 1 from nerve) from separate patients, were shown to be fully sensitive to dapsone. The importance of these findings is discussed, especially with regard to clinical relapse of leprosy after premature stopping of treatment and to the total duration of dapsone therapy required in lepromatous leprosy.