The Equine Movement Disorder "Shivers" Is Associated With Selective Cerebellar Purkinje Cell Axonal Degeneration.
Authors: Valberg S J, Lewis S S, Shivers J L, Barnes N E, Konczak J, Draper A C E, Armién A G
Journal: Veterinary pathology
Summary
# Editorial Summary: Shivers and Cerebellar Pathology Shivers has long presented a diagnostic puzzle in equine practice—horses exhibit characteristic difficulty backing, hyperflexed limb postures, and tremoring specifically during rearward movement, yet conventional neurological examination often appears normal. Valberg and colleagues conducted detailed neuropathological analysis of the entire sensorimotor system in affected horses and controls, employing immunohistochemical labelling and electron microscopy to identify cellular and ultrastructural lesions throughout the central and peripheral nervous systems. The critical finding was an 80-fold increase in degenerating axonal spheroids within Purkinje cell terminals in the deep cerebellar nuclei of shivers horses—specifically those positive for calbindin and glutamic acid decarboxylase—alongside unusual myelin decompaction structures not seen in controls, whilst peripheral nerves and muscles remained entirely normal. This represents the first definitive neuropathological locus for shivers, localising the disease to cerebellar output pathways, which explains the context-specific nature of clinical signs: the cerebellum's role in coordinating and modulating movement becomes particularly critical during complex tasks like backing. For practitioners, this discovery opens potential avenues for earlier diagnosis through cerebrospinal fluid biomarkers or advanced imaging, whilst highlighting that shivers is a primary neurological disease rather than a peripheral or musculoskeletal problem, which should inform both management strategies and realistic expectations regarding progression.
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Practical Takeaways
- •Shivers is a primary central nervous system disorder affecting cerebellar control of movement, not a muscular or peripheral nerve problem, which should guide diagnostic and management approaches
- •The selective cerebellar pathology explains why forward movement is typically normal while backward movement is severely affected—this pattern should alert practitioners to consider cerebellar dysfunction when evaluating movement disorders
- •Currently no cure is available; management should focus on adapting work and training to accommodate the progressive nature of cerebellar degeneration rather than expecting resolution with conventional treatments
Key Findings
- •Shivers is characterized by selective cerebellar Purkinje cell axonal degeneration in the deep cerebellar nuclei, not peripheral nerve or muscle pathology
- •Calretinin-negative, calbindin-positive, and glutamic acid decarboxylase-positive axonal spheroids were increased 80-fold in Purkinje cell axons of affected horses compared to controls
- •Ultrastructural analysis revealed unusual myelin decompaction and lamellar membranous structures in presumed Purkinje cell axons of shivers horses but not controls
- •The pathologic findings explain the clinical presentation of backward movement difficulty, hyperflexed postures, and hind limb tremors as context-specific cerebellar hypermetria and myoclonus