Acquired Neuropathies Figure 4. Alterations of nodal and paranodal proteins in chronic acquired neuropathies. Immunolocalization of paranodin (Pnd, green), voltage-gated Na+ channels (Nav, red) in longitudinal sections of superficial peroneal nerves (A–I). In blue is shown nuclear staining with topro-8 (E, I) and neurofilaments (Nf, F). B, D, and H are higher magnifications of A, C, and G, respectively. A, B. In a control nerve paranodin and Nav are correctly localized in the paranodal (arrows) and nodal (asterisks) regions, respectively. C, D. In CIDP (Patient 1), paranodin immunoreactivity extends to the internodal regions (double arrows). Nav immunoreactivity remains concentrated in some fibers (asterisk), while it has a diffuse, punctuate pattern along other fibers (arrow). E. Another CIDP case (Patient 6) with paranodin immunostaining (double arrows) extending in the internode. Nodal regions are indicated (asterisks). F. In CIAP (Patient 14), in some fibers the paranodal staining appears irregular (arrow). Neurofilaments are in blue. G, H. In CIAP patient 20, paranodin immunoreactivity is irregular in some nerve fibers with an asymmetrical localization (arrow), whereas the nodal expression of Nav appears normal (asterisk). A diffuse Nav-like immunoreactivity can be detected along some axons (arrowhead). I. In another CIAP Patient 13, an interrupted paranodal region (arrow) is visible at high magnification, followed by the normal paranodin staining along the mesaxon. Scale bar: A, C, E, F, G, 40 mm; B, D, H, 20 mm; I, 1.7 mm. doi:10.1371/journal.pone.0014533.g004 demyelination, hypomyelinated fibers, and onion bulbs [28,29]. These lesions are variably observed and depend when the biopsy is performed in the course of the disease. CIAPs are characterized by variable axonal loss, features of axonal regeneration (regeneration clusters) and no or very few demyelinating lesions [30]. However, the difference between CIDP and CIAP may be difficult to establish [30,31]. In the present study we investigated the existence of alterations of nodes of Ranvier in biopsies from patients with chronic acquired neuropathies since these regions are critical for the function of myelinated fibers and the site of early myelin changes in demyelination [32]. We then examined whether some of these alterations might help for the diagnosis. Although electron microscopy of transverse sections of periph- eral nerves is a classical approach that can contribute to the diagnosis of peripheral neuropathies, longitudinal sections are rarely, if ever, used. Nodes of Ranvier that are not easily investigated in transverse sections have not been characterized in these conditions. Here we specifically investigated the ultrastruc- PLoS ONE | www.plosone.org 5 January 2011 | Volume 6 | Issue 1 | e14533