Unilateral degenerative joint disease of a cervical articular process joint between the fourth and fifth cervical vertebrae causing asymmetrical ataxia in a young horse
Authors: Bailey J., Bowen I. M., Anghileri B., Baiker K., Henson F. M. D.
Journal: Equine Veterinary Education
Summary
# Editorial Summary A 5-year-old horse presenting with asymmetrical ataxia and paresis underwent comprehensive neurological investigation combining clinical examination, magnetic motor evoked potentials (which demonstrated abnormal conduction times to the right thoracic and pelvic limbs), radiography, and contrast-enhanced CT imaging. The CT scan revealed unilateral degenerative joint disease of the right articular process joint between C4 and C5 with dorsolateral spinal canal impingement, explaining the asymmetrical cervical myelopathy localised on neurological testing. Post-mortem examination and histopathological analysis revealed an important finding: the unilateral right-sided compression had induced bilateral degenerative changes within ascending and descending spinal tracts, indicating that this lesion possessed a dynamic component despite appearing structurally static on imaging. This case demonstrates that unilateral cervical articular process joint disease can cause severe neurological dysfunction and highlights how spinal cord pathology may be more complex than static compression alone would suggest. For practitioners, this case underscores the diagnostic value of combining advanced imaging with electrophysiological testing in cervical myelopathy cases and emphasises that even unilateral structural lesions warrant careful prognostication due to potential for progressive cord degeneration.
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Practical Takeaways
- •Asymmetrical ataxia with abnormal neurological findings warrants cervical spine investigation; standard radiographs may miss articular process pathology—consider CT or MRI for definitive diagnosis
- •Unilateral cervical joint disease can produce bilateral spinal cord changes through dynamic compression mechanisms during movement, affecting prognosis and performance potential
- •Magnetic motor evoked potentials are a useful diagnostic tool to confirm cervical myelopathy when clinical localization suggests spinal cord involvement
Key Findings
- •Unilateral right-sided degenerative joint disease of C4-C5 articular process caused asymmetrical ataxia with abnormal motor conduction times to ipsilateral thoracic and pelvic limbs
- •Contrast-enhanced CT revealed dorsolateral spinal canal impingement from enlarged articular process joint that was not visible on radiographs
- •Post-mortem histology showed bilateral degenerative changes in ascending and descending spinal cord tracts despite unilateral compression, indicating dynamic rather than static lesion behavior
- •Magnetic motor evoked potentials successfully localized cervical spinal myelopathy before advanced imaging confirmation