DISTAL SENSORIMOTOR POLYNEUROPATHY IN MATURE ROTTWEILER DOGS

A polyneuropathy recognized in mature Rottweiler dogs is characterized by paraparesis that progresses to tetraparesis, spinal hyporeflexia a nd hypotonia, and appendicular muscle atrophy. Although signs may appe ar acutely, the course tends to be gradually progressive (up to 12 mon ths or longer in some dogs) and may be relapsing. Nerve and muscle bio psies were examined from eight affected Rottweilers (six male and two female) between ages 1.5 and 4 years. Pronounced neurogenic atrophy wa s present in skeletal muscle samples. Changes in sensory and motor per ipheral nerves included loss of myelinated nerve fibers, axonal necros is, and variable numbers of fibers with inappropriately thin myelin sh eaths. Ultrastructural findings included myelinated fibers showing mye linoaxonal necrosis, demyelinated fibers often associated with macroph age infiltration, many axons with myelinlike membranous profiles, incr eased endoneurial collagen, occasional axonal atrophy, and numerous Bu ngner bands. Lesions in unmyelinated fibers included increased numbers of Schwann cell profiles and loss of axons in Schwann cell subunits. Morphologic and morphometric studies indicated preferential loss of me dium (5.5-8 mu m) and large (8.5-12.5 mu m) fibers, which was more sev ere in distal parts of nerves than in more proximal regions and nerve roots. The cause was not determined; however, histopathologic studies suggest this condition is a dying-back distal sensorimotor polyneuropa thy that has morphologic and morphometric similarities to hereditary m otor and sensory neuropathy (HMSN) type II in humans.