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Motor neuron disease (Brittany Spaniel)
Synonym(s): Spinal muscular atrophy in Brittany Spaniel, Hereditary canine spinal muscular atrophy, HCSMA
Introduction
- Cause: dominantly inherited lower motor neurone disease.
- Three clinical pictures, accelerated, intermediate and chronic.
- Homozygotes show the accelerated disease, heterozygotes the intermediate or chronic phenotypes.
- Signs: begin before the puppy reaches maturity and progress.
- Progressive weakness with muscle atrophy.
- Treatment: none.
- Prognosis: accelerated and intermediate forms progress until the puppy is unable to walk.
Presenting signs
Early onset or accelerated disease
- Onset between 6-8 weeks of age.
- Progressive onset weakness.
- Slow head tremor.
- Weakness of muscles of mastication and tongue.
- Feeding difficult.
- Become tetraparetic or tetraplegic.
- Unable to lift their heads by 3-4 months old
- Affected puppies thinner than litter mates (30% weight loss due to muscle atrophy).
- Gag reflex depressed.
Intermediate disease
- Onset of clinical signs before puppy reaches maturity.
- Family history of the disease in one or more parent.
- Unable to walk by 2-3 years of age.
- Intercostal muscle involvement may reduce respiratory distress.
Chronic disease
- Late onset mild clinical signs.
- Weakness, muscle atrophy at 1-2 years of age.
- Slowly progressive.
- Thin.
- Survive for 7 years or more with minimal motor involvement.
Age predisposition
- Onset at 6-12 weeks old (accelerated disease).
- Onset at 6 months-3 years (intermediate disease).
- Onset at 1-2 years (chronic disease).
Breed/Species predisposition
- Brittany Spaniel Brittany.
Cost considerations
- Moderate expenses incurred for diagnostic work-up.
Special risks
- Aspiration pneumonia Lung: aspiration pneumonia; decubital ulcers from recumbency.
Pathogenesis
Etiology
- Inherited by an autosomal dominant trait.
- Dogs that are homozygous for the trait develop clinical signs between 6 and 8 weeks of age and rapidly progress (accelerated disease) with death ensuing by 4 to 5 months of age.
- Heterozygotes for the trait are divided into intermediate and chronic forms phenotypically.
Pathophysiology
- Premature degeneration of the cell bodies of motor neurones.
- Impaired slow-axonal transport of cytoskeletal proteins, neurofilament proteins and tubulin → build up of material in axons → axonal swelling.
- Altered levels of choline acetyltransferase activity.
- Possible alteration in spinal cord glutamate activity.
- Premature degeneration and death of neuronal cell populations in the spinal cord and brain stem → interruption of nerve impulses to skeletal muscle → decreased or absent reflexes, muscle tone, and voluntary movement → progressive muscle atrophy (seen as prominent thinness and loss of bodyweight).
- Although there are some indicators of oxidative stress (changes in vitamin E and serum copper levels), these are more likely to be an effect of the disease than a cause.
Timecourse
- Accelerated disease has a course of about 2 months.
- Intermediate disease has a course of 1-2.5 years.
- Chronic disease has a protracted course of several years.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Olby N (2004) Motor neuron disease: inherited and acquired. Vet Clin Small Anim 34 (6), 1403-1418 PubMed.
- Green S L, Bouley D M, Pinter M J et al (2001) Canine motor neuron disease: clinicopahtological features and selected indicators of oxidative stress. J Vet Intern Med 15 (2), 112-119 PubMed.
- Braund K G (1996) Degenerative causes of neuropathies in dogs and cats. Vet Med 91 (8), 722-739 VetMedResource.
- Sack G H et al (1996) Canine genetic linkage study using heterologous DNA probes. J Hered 87 (1), 15-20 PubMed.
- Cork L C et al (1990) Hereditary canine spinal muscle atrophy - canine motor neurone disease. Can J Vet Res 54 (1), 77-82 PubMed.
- Cork L C et al (1982) Pathology of motor neurons in accelerated hereditary canine spinal muscular atrophy. Lab Invest 46 (1), 89-99 PubMed.
- Lorenz M D et al (1979) Hereditary spinal muscular atrophy in Brittany Spaniels - clinical manifestations. JAVMA 175 (8), 833-839 PubMed.