Mieloencefalopatia Degenerativa Equina: Características Clínicas e Histopatológicas e Diagnósticos Diferenciais

Resumo

Background: Equine degenerative myeloencephalopathy (EDM) is a neurodegenerative disease that appears to be associated with an early deficiency of vitamin E and suspected genetic inheritance. However, other causes such as scarce or low-quality pastures and intoxication by pyrethrins or pyrethroids have already been reported. Equine degenerative myeloencephalopathy has already been described in several breeds; there is no predisposition by sex, and foals up to two years of age are the most affected animals. The objective of this study is to report the case of an adult mare with EDM as well as clinical and histopathological features of the disease and the main differential diagnoses.

Case: A 10-year-old, 400-kg Quarter Horse (QH) mare presented with nonspecific neurological signs such as proprioception deficit and progressive asymmetric ataxia of the hindlimbs with a three-month evolution. The hypothesis of traumatic injury was firstly considered; nonetheless, after being subjected to a stressful condition, there was worsening of the ataxia and the ability to stand by itself. A condition of Equine Protozoal Myeloencephalitis (EPM) was hypothesized and therapy with anticoccidial was initiated and maintained for 30 days. Due to the lack of clinical improvement, the owner opted for euthanasia. Necropsy was performed and central nervous system samples were collected. Macroscopically, there were no medullary alterations, whereas microscopy showed areas of axon degeneration and spongiosis involving the white matter and gray matter in the cervicothoracic segments and in the brainstem, specifically in the tectospinal, reticulospinal, anterior spinocerebellar, and dorsal spinocerebellar tracts and gracile and cuneiform fasciculi, confirming the diagnosis of EDM.

Discussion: This is the first reported case of EDM in Brazil, there being only one report of its variant in a mule. In the case, manifestations appeared at 10 years of age and the presented ataxia was asymmetrical with pivoting on the left limb, contrary to that reported in the literature. However, histopathological examination revealed a difference in the lesion pattern, with the left side being slightly more affected. Among the causes mentioned for the development of the disease, the hereditary or breed factor in this case cannot be ruled out. In an American study, horses diagnosed with EDM (38/265) were 2.95 times more likely to be a Quarter Horses. Given this assumption, EDM should be considered as a differential diagnosis in QH of all ages that present with proprioceptive ataxia of medullary origin.