Renaut bodies in the hind limb nerves of cattle with downer cow syndrome

Abstract

Renaut bodies are loosely textured, whorled, cell-sparse structures that are located in the sub-perineurial area of peripheral nerves. Renaut bodies have been previously recognized in human beings and some animal species. Pathogenesis of the structures is not fully understood. In the present study, peripheral nerves of four adult Holstein-Friesian dairy cows affected with the downer cow syndrome were investigated histopathologically. The animals were culled 3 days (one case), 12 days (one case), or 11 days (two cases) after the onset of clinical signs indicative of motor dysfunction, such as hind limb paralysis, inability to rise, and recumbency. Histopathological lesions which had important clinical implications were recognized in the thigh muscles that presented extensive degeneration (necrosis) of muscle fibers in all four cases. In two cases, the sciatic nerve showed Wallerian degeneration of myelinated nerve fibers, while in two other cases, multiple Renaut bodies instead of these degenerative changes were found in the sub-perineurial area of almost all nerve bundles in either the left femoral nerve or left sciatic nerve. Renaut bodies were composed of loosely and circumferentially arranged collagen fibers and fibrocytes, giving rise to an appearance of circular or onion-like swirls. Pathogenesis of the Renaut bodies remained undetermined. There was no convincing histopathological evidence to suggest that such unique intraneural structures were implicated in the development of the cows’ clinical deficits.