Canine degenerative myelopathy
Canine degenerative myelopathy (DM) is an adult onset, progressive neurodegenerative disease of the spinal cord. Most dogs are at least 8 years old before the onset of clinical signs. The initial signs of degenerative myelopathy typically include asymmetric general proprioceptive ataxia and spastic paresis in the pelvic limbs. At this stage, segmental spinal reflexes are indicative of upper motor neuron loss. The disease duration can exceed 3 years, however, its progression is relentless, and dog owners usually elect euthanasia within a year of diagnosis when their dogs become paraplegic. When euthanasia is delayed, weakness can ascend to the thoracic limbs with the emergence of lower motor neuron signs such as flaccid tetraplegia, widespread muscle atrophy, dysphagia, and inability to bark.
Because a variety of common acquired compressive spinal cord diseases can mimic the early signs of degenerative myelopathy by compromising upper motor neuron pathways, a definitive diagnosis of degenerative myelopathy can only be made postmortem by the histopathologic observation of axonal and myelin degeneration along with astrogliosis in spinal cord funiculi. This disease occurs in all dog breeds, but some breeds including the Pembroke Welsh corgi, Boxer, Rhodesian ridgeback, Chesapeake Bay retriever and German shepherd dogs are particularly susceptible, with 30 – 90% homozygous affected dogs, mostly differing relative to geographic positions.