Length-dependent degeneration of fibers in Portuguese amyloid polyneuropathy: a clinicopathologic study.

We investigated two patients with Portuguese amyloid polyneuropathy to learn more about the role played by amyloid in this condition. In sural nerves, axonal loss predominated in unmyelinated axons. Different abnormalities of single fibers near amyloid deposits included distortion of the myelin sheath, segmental demyelination, and wallerian degeneration. Electronmicroscopic studies showed degenerative changes of endoneurial cells in contact with fibrils of amyloid. Therefore, amyloid plays an important role in the length-dependent degeneration of fibers of this condition. Why unmyelinated fibers are so heavily affected remains unclear.