ABSTRACT To describe the ultrastructural characteristics of axon cytoskeleton alterations occurring during axonopathies of unknown aetiology (AUE), and necrotizing angeitis (NA), which are partly unknown. We have analyzed by transmission electron microscopy nerve biopsies from 8 and 6 cases of AUE and NA, respectively, in which previous studies by optic microscopy had shown decreased fibre immunostaining for neurofilament (NF), contrasting with increased labelling for α tubulin. Morphometry was performed in fibres devoid of obvious degeneration signs. NF and microtubule (µT) density, as well as minimal inter-NF distance were measured in 10 myelinated fibres per class of diameter, and compared to controls (without neurologic involvement). In most cases of AUE and NA a severe decrease in NF density was observed, it associated with an increase in µT density in AUE only. Variability of cytoskeleton alterations could be extreme, i.e. NF decreased by 5-fold in some cases, or NF density could be nearly normal. In AUE µT increased by 5 to 10-fold, whereas they decreased in NA in one case excepted. These results confirm those of immunostaining for NF in AUE and in NA, and demonstrate that decreased NF immunostaining corresponds to a decrease in NF density in residual fibres and could not be ascribed simply to fibre loss. Abnormal NF synthesis (AUE), or increased degradation (NA), could account for this pattern. Since this study was performed on apparently non-degenerating fibres, it highlights also an unsuspected extent of axonal damage in these neuropathies.
View Full Article
|