Equine degenerative myeloencephalopathy

EDM is a neurologic disease of young horses characterized by the insidious development of symmetric ataxia. Decreased or absent cutaneous trunci reflex or slap test responses are considered clinical signs that increase the index of suspicion for this disease. In addition, concurrent predisposing factors, such as familial history, inadequate access to green pasture, and possible exposure to wood preservatives or insecticides, provide further supporting evidence for a clinical diagnosis. Vitamin E deficiency and a hereditary predisposition currently are considered the most significant factors in the pathogenesis of this disease. Histopathologically the lesions of EDM are those of neuraxonal dystrophy, characterized by prominent axonal and dendritic swelling, mild glial proliferation, and neuronal depletion and atrophy with lipofuscin-like pigment accumulation. Animals predisposed to EDM or with a clinical diagnosis of EDM should receive oral alpha-tocopherol acetate supplementation. Improvement in clinical signs may be seen following long-term treatment, but in general, the prognosis for complete recovery is poor.