Post-mortem morphological alterations of human peripheral nerve

Post-mortem morphological modifications in median nerve samples collected at different times after death were studied in subjects with known circumstances and times of death. Histological analyses were performed by light and electron microscopy on single fiber and on transversal sections. Results of morphological observations evidenced the progressive disappearance of myelin over time according to a process similar to Wallerian degeneration occurring in vivo. Electron microscope analysis of transversal sections evidenced four steps through which post-mortal myelin degradation proceeded, from the initial structure modification (after 12 h from death) to the complete collapse and the simultaneous appearance of dropsy bumps toward the axon (after 48 h from death). The post-mortal demyelinization process can reasonably be thought to have a multifocal origin. Post-mortem alterations of nerve fibers do not evolve simultaneously and in a uniform manner in all the fibers of the same nerve, where different factors come into play, particularly fiber gauge.