Histopathological assessment of intrinsic laryngeal musculature in horses with dynamic laryngeal collapse.
Authors: Fjordbakk C T, Revold T, Goodwin D, Piercy R J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Laryngeal Muscle Pathology in Dynamic Laryngeal Collapse Dynamic laryngeal collapse (DLC) associated with excessive poll flexion has long puzzled practitioners, with neuromuscular dysfunction suggested as a potential mechanism; however, Fjordbakk and colleagues' 2015 histopathological investigation challenges this assumption by examining whether the intrinsic laryngeal muscles in affected horses show evidence of denervation or paresis. Five DLC-affected horses and eight controls underwent detailed muscle analysis using immunofluorescence microscopy to assess fibre type proportions, fibre diameter and fibre type grouping patterns in the dorsal cricoarytenoid, lateral cricoarytenoid and cricothyroid muscles. Contrary to expectations of neurogenic atrophy, no statistically significant differences emerged in fibre size, fibre type proportions or bilateral symmetrical grouping changes between DLC cases and controls, although objective analysis did reveal scattered asymmetrical fibre clustering—findings inconsistent with a primary neuromuscular aetiology. The implications for practice are substantial: if DLC cannot be attributed to muscle denervation or intrinsic weakness, the underlying cause likely involves biomechanical factors (excessive poll flexion mechanics, cervical stability, structural conformational issues) or alternative systemic mechanisms, potentially redirecting diagnostic and therapeutic approaches away from neuromuscular assessment and towards postural, anatomical and functional evaluation during ridden work.
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Practical Takeaways
- •DLC in horses with poll flexion is unlikely caused by intrinsic laryngeal muscle weakness or denervation; practitioners should consider non-neuromuscular causes such as mechanical or conformational factors
- •The symmetry and distribution of muscle changes typical of neurogenic disease were absent, indicating that poor laryngeal function in affected horses cannot be attributed to muscle degeneration alone
- •Further investigation into alternative mechanisms of DLC pathogenesis (mechanical, structural, or biomechanical) is warranted to guide treatment approaches
Key Findings
- •No statistically significant differences in fibre type proportions, fibre size, or subjective fibre type grouping between DLC-affected horses (n=5) and unaffected controls (n=8)
- •Objective assessment revealed inconsistent fibre type grouping differences between groups that were not symmetrically distributed, inconsistent with neuromuscular pathology
- •Histopathological findings do not support a neuromuscular component in the pathogenesis of DLC, suggesting alternative aetiologies should be investigated