Sural nerve biopsy findings in leprosy: a qualitative and quantitative light and electron microscope study in 4 treated cases of the lepromatous spectrum

Reports on biopsy findings in multifascicular nerves in lepromatous leprosy (LL) are rare and detailed morphometrical data are not available. In a case of early LL with normal electrodiagnostic findings in sural nerve, the present study revealed marked segmental de- and remyelination concomitant with the sequelae of considerable Wallerian degeneration of preferentially small myelinated fibers (MF) in spite of a normal number/nerve and density/mm2. Segmental de- and remyelination of several consecutive internodes in teased fibers suggests continuous bacterial spread via Schwann cells. In 2 more advanced LL-cases, nervous parenchyme was severely reduced, in a borderline lepromatous (BL) case obviously in part caused by cell infiltrates and granulomata. Distinct fascicle differences in MF-involvement were demonstrated by coefficients of variation of MF/mm2 and teased fiber preparations in LL, consistent with the hypothesis of initial focal spread of bacteria. Numbers and densities of endoneurial vessels were increased only in the later stages of LL. Enlargement of endoneurial area, due to different factors, was encountered except for the most severe LL-case with extensive endoneurial collagenization. Morphometric results were compared with those of other neuropathies. Intact and degenerating bacteria mostly in phagosomes of Schwann cells associated with unmyelinated axons and in macrophages were seen only in the early LL- and the BL-case. Sparse mononuclear cell infiltrates and small focal necrosis, present even in LL-cases, underline the complex pathogenesis of nerve fiber involvement.