Progressive axonopathy

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Progressive axonopathy (Boxer neuropathy) is an autosomal-recessive genetic sensory neurological disease of Boxers characterized by a gradual loss of sensation to the limbs.

This condition, which is hereditary, is thought to be due to degenerative changes within sensory nerves of teh central and peripheral nervous system caused by aberrations in intra-axonal protein transport.

Clinically affected pups show progressively worsening clinical signs of ataxia and hypermetria from one to two months of age[1]. Distal limb muscles show varying, but usually minor, degrees of neurogenic atrophy[2] starting with reduced patella reflexes.

Proprioceptive function, muscle tone and tendon reflexes are usually diminished or absent[3] and neurological signs tend to progress slowly until the dogs are 12 - 18 months of age then tend to stabilize. The dog may lose sensation in the feet, may take very extended steps and have decreased strength in the legs. The condition progresses to the front legs and the dogs develop head bobbing and flickering of the eyes[4].

Diagnosis can be difficult and routine blood tests, radiographs, CT or MRI imaging may be required to differentiate other causes of neurological disease. Electromyographic studies and muscle biopsies are usually required to assist a diagnosis.

Histologically, this disease appears as increased neurofilaments (mainly actin and myelin-associated glycoprotein[5]) within the nerve roots of lumbar ventral roots, spinal cord and central nervous system[6]. As the disease progresses, progressively more fibres demonstrate short internodes of irregular length and thin myelin sheaths suggesting extensive remyelination and remodelling of the sheath[7].

A differential diagnosis would include other causes of polyneuropathy such as polyradiculoneuritis as well as Toxoplasma spp and Neospora spp infections and tick paralysis.

There is no known treatment for this condition and because of the hereditary nature of this condition, affected dogs should not be used for breeding. Most affected dogs remain clinically stable for years and ambulatory and may be acceptable pets.

References

  1. Griffiths IR et al (1986) Progressive axonopathy: an inherited neuropathy of boxer dogs. 3. The peripheral axon lesion with special reference to the nerve roots. J Neurocytol 15(1):109-120
  2. Griffiths IR et al (1985) Progressive axonopathy: an inherited neuropathy of boxer dogs. 2. The nature and distribution of the pathological changes. Neuropathol Appl Neurobiol 11(6):431-446
  3. Vetstream
  4. LIDA
  5. Griffiths IR et al (1989) The distribution of MAG in association with the axonal lesions of canine progressive axonopathy. J Neurocytol 18(3):353-358
  6. Griffiths IR et al (1989) Progressive axonopathy: an inherited neuropathy of boxer dogs. An immunocytochemical study of the axonal cytoskeleton. Neuropathol Appl Neurobiol 15(1):63-74
  7. Griffiths IR et al (1987) Progressive axonopathy: an inherited neuropathy of boxer dogs. 4. Myelin sheath and Schwann cell changes in the nerve roots. J Neurocytol 16(2):145-153