Polyneuropathy in Greyhound show dogs.

Most consistent findings in affected dogs (A, C, E, G, H, I) compared to healthy controls (B, D, F). (Scale bar: 100 µm in C and D; 125 µm in E and F; 10 µm in G and H; 17 µm in I). (A, B) General appearance: Affected dogs during ambulatory stages present with abnormal posture characterized by narrow limb positioning and mildly kyphotic backline (arrow). (C, D) Light microscopic nerve findings: At advanced disease stages mixed nerves show a drop out of large myelinated A(alpha) fibres, including motor fibres and Ia/b afferents. Remaining fibres frequently present with axonal atrophy and subsequent myelin sheath adjustment (frame). Multiple myelin ovoids indicate Wallerian like degeneration (black arrowheads). Hypomyelinated profiles are occasionally seen (white arrowhead). (E, F) Teased nerve fibres: Nerve of affected dogs show multifocal paranodal demyelination (red arrowhead), frequently associated with axonal swelling (asterisk). Numerous fibres with and without other abnormalities are affected by myelin sheath segmentation (red arrows), consistent with early stage I of Wallerian degeneration. Compare to normal myelinated nerve fibres with discernible Ranvier's nodes (RN) and stereotypic internodal segments (STIN). (G) Electron microscopy: Swollen axons (Ax) show an accumulation of dysmorphic organella, electron dense granules, and lamellated bodies (asterisk). In spite of increased axon diameters the myelin sheath (MS) most often is disproportionately thin. (H) Electron microscopy: Actual fibre degeneration occasionally starts with axoplasmic disintegration (Ax) and macrophageal (Mac) myelin stripping from the abaxonal Schwann cell cytoplasm extending along the major dense lines (yellow arrowhead). (I) Electron microscopy: Fibres with shrunken axons (Ax) show adaxonal myelin sheath protrusion, dyscompaction of the inner myelin layers (yellow arrow), and accumulation of dysmorphic mitochondria and curvilinear bodies (red arrow).