ISSN 2398-2977      

CNS: myeloencephalopathy - degenerative

pequis

Synonym(s): EDM


Introduction

  • Inherited progressive neurodegenerative disorder of the central nervous system (CNS).
  • Cause: etiology unknown; genetic familial predisposition triggered by environmental factors such as vitamin E deficiency.
  • Signs: symmetric tetraparesis and ataxia in foals and young horses.
  • Diagnosis: clinical signs and elimination of other neurogenic and neuromuscular syndromes. Post-mortem histopathology changes.
  • Treatment: none available. Supplementation of vitamin E may stabilize clinical signs but is not curative.
  • Prognosis: slowly progressive condition which may stabilize as animal matures.

Pathogenesis

Etiology

  • Equine neuroaxonal dystrophy (eNAD) which causes specific damage to neurons in the brainstem and spinal cord is the underlying basis for EDM.
  • EDM and eNAD are not distinguishable clinically but EDM is the more advanced form.
  • Many breeds are affected but an increased incidence in closely related horses is highly suggestive of a genetic basis to the disease. An autosomal dominant mode of inheritance with incomplete penetrance has been identified. An actual mutation has not been identified yet but research is ongoing.
  • An environmental trigger is required in animals that are genetically predisposed to initiate disease. Research has shown this is dietary vitamin E deficiency. Vitamin E Vitamin E is a biological antioxidant which is essential for normal neurological function by decreasing oxidative stress and free radical damage. The deficiency must occur during specific developmental stages of the animal to cause clinical signs.
  • Other risk factors suggested in earlier reports included prior use of insecticides and exposure to wood preservatives both of which contain antioxidants, although this has not been confirmed in later studies.

Predisposing factors

Specific

  • Access to dirt lots, use of heated pelleted feed and sunbaked forages with low vitamin E contents.
  • Lack of access to fresh green grass.
  • Familial tendency.

Pathophysiology

  • Progressive diffuse spinal cord disease → tetraparesis and ataxia.
  • Diffuse degenerative disease of the caudal brainstem and spinal cord that affects proprioceptive relay nuclei as well as dorsal and ventral spinocerebellar tracts.
  • The histologic lesions in eNAD are confined to the cuneate and gracile nuclei of the caudal medulla oblongata, while in EDM, the lesions are more widespread and include demyelination within the ascending tracts of the spinal cord. Immunohistochemical calretinin staining has defined afferent proprioceptive tracts as the primary tracts damaged in eNAD/EDM horses, and isolated soma within the dorsal root ganglia as the source of dystrophic axons.

Timecourse

  • Once signs of EDM appear the disease is usually slowly progressive, although some cases may stabilize with maturity.
  • No significant improvement/remission is seen with age.

Epidemiology

  • The disease may occur in individuals or may affect a group of animals at the same time (usually related).

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.
  • Finno C J et al (2017) Pigment retinopathy in warmblood horses with equine degenerative myeloencephalopathy and equine motor neuron disease. Vet Ophthalmol 20 (4), 304–309 PubMed.
  • Finno C J et al (2016) Concurrent equine degenerative myeloencephalopathy and equine motor neuron disease in three young horses. J Vet Intern Med 30 (4), 1344–1350 PubMed.
  • Finno C J et al (2016) Evidence of the primary afferent tracts undergoing neurodegeneration in horses with equine degenerative myeloencephalopathy based on calretinin immunohistochemical localization. Vet Pathol 53 (1), 77–86 PubMed.
  • Finno C J et al (2015) Blood and cerebrospinal fluid α-tocopherol and selenium concentrations in neonatal foals with neuroaxonal dystrophy. J Vet Intern Med 29 (6), 1667–1675 PubMed.
  • Finno C J et al (2013) Pedigree analysis and exclusion of alpha-tocopherol transfer protein (TTPA) as a candidate gene for neuroaxonal dystrophy in the American Quarter Horse. J Vet Intern Med 27 (1), 177–185 PubMed.
  • Wong D M et al (2012) Evidence of oxidative injury of the spinal cord in 2 horses with equine degenerative myeloencephalopathy. Vet Pathol 49 (6), 1049–1053 PubMed
  • Aleman M et al (2011) Evaluation of epidemiological, clinical, and pathological features of neuroaxonal dystrophy in Quarter Horses. JAVMA 239 (6), 823–833 PubMed.
  • Nayler R J (2010) Equine degenerative myeloencephalopathy in a horse in the UK. Vet Rec 167 (10), 380-382 PubMed.
  • Higgins J K et al (2008) Assessment of vitamin E concentrations in serum and cerebrospinal fluid of horses following oral administration of vitamin E. Am J Vet Res 69 (6), 785–790 PubMed.
  • Gandini G et al (2004) Equine degenerative myeloencephalopathy in five quarter horses: clinical and neuropathological findings. Equine Vet J 36 (1), 83–85 PubMed.

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