Presumptive motor neuron degeneration in an adult cat.

An 8-year-old neutered male Bengal cat was referred because of a 1-year history of progressive and relapsing generalized muscle weakness and muscle atrophy. Before referral, the cat was treated with immunosuppressive doses of oral prednisolone, intermittently for 6 mo, and had responded well when the immunosuppressive dose was maintained. Generalized paresis, diffuse muscle atrophy, and diminished spinal reflexes were present in all limbs, consistent with a generalized lower motor neuron disease. Histopathologic evaluation of muscle biopsies confirmed a pattern of muscle fiber atrophy consistent with chronic and severe denervation. No specific abnormalities were identified in the nerve biopsy or within intramuscular nerve branches. A presumptive antemortem diagnosis of an adult-onset motor neuron degeneration resembling amyotrophic lateral sclerosis (ALS) or spinal muscle atrophy was suspected. However, given the response to immunosuppressive doses of corticosteroids, an autoimmune process or other degenerative process could not be definitively excluded. Key clinical message: In this case, an adult cat had a chronic, progressive history of lower motor neuron weakness and absent spinal reflexes; biopsies revealed a neurogenic pattern of muscle fiber atrophy and histologically normal peripheral nerve and intramuscular nerve branches. Although reports of motor neuron disease are rare in the veterinary literature, this case report highlights the importance of muscle and nerve biopsies that lead to a presumptive diagnosis of motor neuron degeneration.