Motor Neuron Disease
Spontaneous motor neuron diseases are uncommon in domestic animals. Where they have been subject to study, these disorders invariably demonstrate a familial pattern, occurring in specific breeds of animals such as Brittany Spaniel dogs, Rottweilers and Bouvier des Flandres. Signs are evident in the first year of life and often by a few months of age.
The disease is also called hereditary canine spinal muscular atrophy (HCSMA) and is characterized by degeneration of motor neurons (nerve cells) in the spinal cord and brain stem. The mechanism of the disorder is not known, but recent studies suggest that it may be a form of abnormal programmed cell death. The disease shows striking clinical and pathological features in common with human motor neuron disease.
The first signs usually present as weakness of limbs, and in most cases the disease progresses quickly to global weakness. The congenital form of the disease is characterized by regurgitation, diminished growth, protruding tongue, inability to hold head, unwillingness to move, and weakness in all four limbs. Walking more than a few feet causes a marked increase in respiratory difficulties.
There have been identified several forms of the diseses. In the accelerated form, the disease appears in the preweaning period. Between 6 and 8 weeks, affected puppies, which are usually thinner and less active than their siblings, develop weakness and often show fine, slow tremor of the head. Weakness of the muscles of the tongue and jaw makes feeding difficult. Respiration is shallow.
In the intermediate form, the onset of the clinical signs is more subtle than in accelerated form of the disease. The first signs of the disease usually appear in the first year of live as waddling, rolling gait due to hindleg weakness. Because dogs depend on the respiration to regulate their body temperature, physical activity in HCSMA-affected dogs can be sometimes accompanied by dangerously high body temperature. By 2 to 3 years, most dogs are unable to walk.
In the chronic form, dogs with this form are thinner than normal during most of their lives, although marked changes in gait or other motor functions are not readily observed.
The course of illness depends on a particular variant of the disease, but the illness is often fatal, usually as a result of the involvement of the muscles of respiration and swallowing. In dogs, the disease is considered to be autosomal dominant. There is no cure for HCSMA.
Adapted from
1. Hussni O Mohammed1 , Thomas J Divers2 , Brian A Summers4 and Alexander de Lahunta. Vitamin E deficiency and risk of equine motor neuron disease. Acta Veterinaria Scandinavica 2007, 49:17
2. L C Cork, D L Price, J W Griffin, and G H Sack, Jr. Hereditary canine spinal muscular atrophy: canine motor neuron disease. Can J Vet Res. 1990 January; 54(1): 77–82.
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