Some histological aspects of amyloid polyneuropathy

Two sporadic cases of amyloid polyneuropathy with clinical features corresponding to the Portuguese type of this disease were studied. Histological examination of sural nerve demonstrated a marked loss of myelinated and unmyelinated fibres in the case 1 due to axonal degeneration, high content of fibers with segmental demyelination and the occurrence of several enlarged axons filled with the 10 nm filaments (so-called giant axons). In the case 2 there was total loss of unmyelinated axons and myelinated fibers were nearly completely lacking. In the development of changes in the myelinated fibers their direct compression by amyloid deposits seems to play an important role. It leads to the appearance of both axonal degeneration and segmental demyelination. The latter seems to be due to local compression and it may involved many fibers. In the light of observations reported by other authors the mechanism of changes developing in unmuelinated fibers is explained by the presence of changes in the cells of posterior root ganglia, however the question whether some abnormalities seen in unmyelinated axons could not be related to the pressure exerted by amyloid deposits directly to these fibers, remains open.