Evidence of the Primary Afferent Tracts Undergoing Neurodegeneration in Horses With Equine Degenerative Myeloencephalopathy Based on Calretinin Immunohistochemical Localization.
Authors: Finno C J, Valberg S J, Shivers J, D'Almeida E, Armién A G
Journal: Veterinary pathology
Summary
# Editorial Summary: Neurodegeneration in Equine Degenerative Myeloencephalopathy Equine degenerative myeloencephalopathy (EDM) remains challenging to diagnose because its clinical presentation—symmetric proprioceptive ataxia in young horses—mimics cervical vertebral compressive myelopathy, and the underlying neuropathological changes can be subtle on routine histology. Finno and colleagues used calretinin immunohistochemistry to map sensory nerve tracts in healthy horses and compare them with tissue from EDM-affected animals, examining dorsal root ganglia, spinal cord nuclei, and key proprioceptive pathways including the spinocuneocerebellar and dorsal column-medial lemniscal tracts. Calretinin successfully labelled primary sensory axons and their cell bodies in dorsal root ganglia; in EDM cases, calretinin-positive axonal spheroids (markers of degeneration) accumulated within the cuneate nuclei and thoracic nuclei, whilst the neurons themselves remained unlabelled, indicating that degeneration originates in the sensory neurone soma rather than as a primary motor or central problem. This work provides equine veterinarians and researchers with a reliable histochemical technique to definitively identify and trace affected sensory pathways at necropsy, potentially improving EDM diagnosis and clarifying its pathomechanics as a primary sensory neuronopathy—knowledge that may eventually inform prevention and management strategies for this poorly understood condition.
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Practical Takeaways
- •EDM may be underdiagnosed because clinical signs overlap with cervical vertebral compressive myelopathy; calretinin staining can aid pathological differentiation of these conditions
- •Calretinin immunohistochemistry is now a validated diagnostic tool for confirming primary afferent tract degeneration in suspected EDM cases
- •Understanding that EDM involves sensory axonal degeneration rather than motor neuron disease may inform future treatment approaches and prognosis counseling
Key Findings
- •Calretinin immunohistochemistry successfully traced primary afferent axons in spinocuneocerebellar, dorsal column-medial lemniscal, and dorsospinocerebellar tracts in healthy horses
- •Calretinin-immunoreactive spheroids were present in EDM-affected horses within nuclei cuneatus medialis, cuneatus lateralis, and thoracicus
- •Dorsal root ganglia cell bodies are the likely source of degenerated axons observed in EDM-affected horses
- •Calretinin IHC provides a diagnostic method to identify axonal spheroids and differentiate EDM from other causes of ataxia