Persistence of Mycobacterium leprae in the peripheral nerve as compared to the skin of multidrug-treated leprosy patients.

Skin and nerve biopsies obtained from 18 multibacillary (MB) and 16 paucibacillary (PB) cases of leprosy who had been fully treated by the WHO regimen were assessed for bacterial load using different staining techniques. In addition skin and nerve homogenates of 10 MB cases were tested for 'persistor' Mycobacterium leprae using immunosuppressed mice. While significant amounts of integral bacilli and BCG cross-reactive antigen of M. leprae were detected both in skin and nerve tissues of all the MB cases (100%), 56% of skin and 62% of nerve biopsies of PB cases also showed the presence of BCG cross-reactive antigen. Detection of 'persistor' M. leprae in 2/10 skin biopsies (20%) and 3/10 nerve biopsies (30%) of MB cases was thought to be unexpectedly high after 2 years of MDT.