Clinical and histopathological features in horses with neuroaxonal degeneration: 100 cases (2017‐2021)

Abstract Background Adult horses with proprioceptive ataxia and behavior changes that have histologic lesions consistent with neurodegenerative disease have been increasingly recognized. Hypothesis/Objectives Describe the history, clinical findings and histopathologic features of horses presented to a referral institution with neuroaxonal degeneration. Animals One hundred horses with a necropsy diagnosis of neuroaxonal degeneration compatible with neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM). Methods Retrospective study of horses presented to the University of Pennsylvania, New Bolton Center, between 2017 and 2021 with a necropsy diagnosis of eNAD/EDM. Results Affected horses had a median age of 8 years (range, 1‐22), and the majority were Warmbloods (72). Sixty‐eight horses had behavioral changes, and all 100 had proprioceptive ataxia (median grade, 2/5). Fifty‐seven horses had abnormal findings on cervical vertebral radiographs, and 14 had myelographic findings consistent with compressive myelopathy. No antemortem diagnostic test results were consistently associated with necropsy diagnosis of neurodegenerative disease. All 100 horses had degenerative lesions characteristic of eNAD in the brainstem gray matter, and 24 had concurrent degenerative features of EDM in the spinal cord white matter. Conclusions and Clinical Importance Clinical and histopathologic findings in this large group of horses with neurodegenerative disease were most consistent with eNAD/EDM, but with a different signalment and clinical presentation from earlier descriptions. The increasing occurrence of neurodegenerative disease in horses and the safety risk posed emphasize the importance of focused research in affected horses.