Fellow, Large Animal Neurology New Bolton Center, University of Pennsylvania School of Veterinary Medicine West Chester, Pennsylvania, United States
Background – Equine degenerative myeloencephalopathy/equine neuroaxonal dystrophy (EDM/eNAD) is a common postmortem neurologic diagnosis in North American horses. Though temporal deficiency of antioxidant vitamin E is implicated in the etiology, EDM/eNAD remains a diagnosis of exclusion. A vitamin E-responsive myopathy (VEM) is diagnosed by mitochondrial alterations in highly oxidative type 1 muscle fibers in the sacrocaudalis dorsalis medialis (SCDM) muscle.
Hypothesis/Objectives –We hypothesize that mitochondrial alterations in the SCDM may be a proxy for oxidative damage to the central nervous system (CNS). The objective was to determine what percentage of horses with EDM/eNAD exhibit typical VEM histopathology. We also compared percentages of horses with EDM/eNAD exhibiting low serum vitamin E concentrations and increased serum and CSF phosphorylated neurofilament-heavy (pNF-H) concentrations.
Animals – 38 client-owned horses evaluated between 2021-2022
Methods – Cohort study. Incisional formalin-fixed SCDM biopsies were obtained from horses with postmortem-confirmed EDM/eNAD and histopathology evaluated for mitochondrial alterations using succinate dehydrogenase A stains. Serum [vitamin E] was determined with high-performance liquid chromatography and [pNF-H] determined using sandwich ELISA.
Results – 15/38 horses (39%) with EDM/eNAD at postmortem exhibited comorbid VEM histopathology in SCDM biopsies. 3/21 (14%) exhibited increased serum [pNF-H], and 13/21 (62%) exhibited increased CSF [pNF-H]. 6/31 (19%) had low serum [vitamin E].
Conclusions and clinical importance – SCDM mitochondrial alterations were identified in >1/3 of horses with EDM/eNAD and can be used to increase suspicion of EDM/eNAD antemortem. Future investigation into the frequency of VEM in horses with other neurologic conditions could enable estimation of specificity.
