What is the expected disease progression and prognosis for a dog diagnosed with degenerative myelopathy?

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Degenerative myelopathy (DM) follows a predictable rostral progression from pelvic limb ataxia to flaccid tetraplegia and ultimately respiratory failure, with most dogs euthanized within 6–12 months of clinical onset. The disease begins with asymmetric general proprioceptive ataxia and upper motor neuron paraparesis of the pelvic limbs, advances to paraplegia, then flaccid tetraplegia, and terminates in respiratory dysfunction and brainstem signs.16 The median survival from clinical onset is approximately 19 months in Pembroke Welsh Corgis, with a reported range of 10–37 months in that breed.2 Without intensive rehabilitation, most dogs are euthanized 6–12 months after clinical signs begin.9 Dogs receiving daily intensive rehabilitation have demonstrated a mean survival of approximately 438 days, compared to 274 days with a standard rehabilitation protocol — a meaningful difference in a disease with no disease-modifying therapy.9 Urinary incontinence and respiratory impairment develop in most dogs as the disease advances, and respiratory impairment is the predominant cause of natural death in dogs that are not euthanized.10 Brainstem dysfunction — including signs consistent with cranial nerve involvement — appears in a smaller proportion of dogs at the terminal stage.10 If dogs are not euthanized during early stages and the disease is allowed to progress, respiratory muscle paralysis and death occur approximately 3 years after disease onset.6 Concurrent intervertebral disc protrusion (IVDP) does not appear to meaningfully alter disease trajectory. Dogs with the SOD1 mutation and concurrent IVDP show similar time to euthanasia and time to non-ambulatory status compared to those without IVDP.11 No medical therapy alters disease progression. Epsilon-aminocaproic acid, N-acetylcysteine, and supplementation with Vitamins C and E have been investigated and found to provide no benefit.1 Physical rehabilitation is the only intervention shown to slow progression and prolong