Electron Microscopic Study of Centripetal Demyelination of Cutaneous Nerves Following Skin Granuloma

The "traumatic degeneration" of peripheral nerves has been described by Ram6n y Cajal (16) as representing the alteration of both myelin sheath and axon in the central stump of a damaged nerve, in contrast to Wallerian degeneration in the distal part of the same nerve. Distal nerve degeneration and subsequent regeneration after mechanical injuries of peripheral nerve bundles have been well-documented by electron microcroscopy (2, 3 . 5 . 9 . 10, 11 .12. 15.17. 18.19). However, little information on the ultrastructure of traumatic degeneration in myelinated peripheral nerves is available at present (7). Our previous electron microscopic studies demonstrated that Wallerian degeneration occurs in cutaneous nerves as a result of either mechanical injury of the skin, or granulomatous lesions in the dermis (13, 14). Our interest is now focused on the centripetal changes of cutaneous nerves under the same experimental conditions. Events observed in the proximal part of nerves, which are located far from the skin lesions, represent a peculiar demyelination. In leprosy skin lesions, inB.ltration of macrophages, their derivatives (lepra cells and epithelioid cells) and leukocytes may cause alteration of cutaneous nerves, possibly as a result of the locally increased mechanical pressure. However, the direct invasion of leprosy bacilli or the manifestation of delayed hypersensitivity in mesenchymal cells of nerve bundles may also provoke cutaneous nerve changes. These possibilities make it difficult to understand the causative mechanisms involved in ultrastructural alterations of these nerves in various types of leprosy skin lesions (6).