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EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2022) 34 (7) 340 doi: 10.1111/eve.13579_1
Case Report
Unilateral degenerative joint disease of a cervical articular process joint between the fourth and fifth cervical vertebrae causing asymmetrical ataxia in a young horse
J. Bailey†,*, I. M. Bowen†, B. Anghileri‡, K. Baiker† and F. M. D. Henson†
†School of Veterinary Medicine and Science, University of Nottingham, Nottingham; and ‡Oakham Veterinary Hospital, Oakham, UK *Corresponding author email:
james.bailey@
nottingham.ac.uk
Keywords: horse; ataxia; evoked potentials; computed tomography; myelography; arthropathy
Summary A 5-year-old unbroken Irish Draught horse was examined to further investigate a gait abnormality. The horse had been in the owner’s possession for 4 months with its clinical signs being consistent during this time. The horse was found to have quadrilateral ataxia with the right pelvic and thoracic limbs displaying more severe clinical signs (grade 3/5) than the left (grade 2/5). There were no other abnormalities found during a clinical examination and lameness evaluation. Magnetic motor evoked potentials (MMEPs) were used to
provide an objective measurement of motor tract patency. This involved transcortical magnetic stimulation with a hand- held electromagnetic coil and simultaneous monitoring of electrical activity of the extensor carpi radialis (ECR) and tibialis cranialis (TC) muscles. Conduction times to the left ECR and TC muscles were within established cut-offs, but the latencies acquired to the right ECR and TC muscles were
markedly increased, highly suggestive of cervical spinal cord disease affecting the right-hand side. Laterolateral radiographs were acquired to ensure that
the horse did not have pathology, which would contraindicate general anaesthesia. The horse was anaesthetised, and a computed tomographic (CT) myelogram was obtained. The CT images identified multiple markers of degenerative joint disease associated with the right articular process joint between the fourth and fifth cervical vertebrae (Fig 1). The dye column closely associated with this joint demonstrated spinal cord compression and highlighted an accumulation of soft tissue within the spinal canal. Due to the chronicity, poor prognosis and the horse’s intended use, the horse was subjected to euthanasia and a post-mortem examination completed. Grossly, the spinal cord at the level of the lesion was found to have multiple engorged blood vessels on its surface.
The joint surfaces were examined and found to have fibrillated, fissured cartilage. Formalin-fixed sections of the spinal cord were further evaluated. At the level of the compressive lesion, there were degenerative changes in all white matter tracts (left and right dorsolateral and ventral funiculi). Cranial to the lesion, there were degenerative changes in ascending tracts, and caudal to the lesion, there were degenerative changes in descending tracts confirming the significance of the compressive lesion.
Key points
• Palpation, baited stretches and radiography have a poor diagnostic acuity for cervical disease.
Fig 1: Above: Multiplanar reconstructed contrast-enhanced CT image in the transverse plane at the level of the articular process joints of C4/C5 (right is to the right) showing osteophytes at the axial (white arrow) and abaxial (white arrowhead) aspects of the joint. There are multiple soft tissue densities sitting within the spinal canal (black arrowhead). There is also an appreciable increase in subchondral bone density of both right articular processes compared with the opposite side. Below: Reconstructed CT image in the dorsal plane at the level of the articular process joint (right is to the bottom). The large axial osteophyte is clearly visible here (white arrowhead).
• Magnetic motor evoked potentials show good agreement with the unilateral compression and the more severe pathological features of disease. However, this case highlights that normal MMEPs do not preclude mild pathological changes as seen on the left side of this horse.
• Although MMEPs indicated the unilateral nature of disease, CT myelography was essential to document the articular joint pathology causing the compression and should be considered as the gold standard imaging modality for the investigation of spinal ataxia in the horse.
© 2021 EVJ Ltd
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