The Equine Movement Disorder "Shivers" Is Associated With Selective Cerebellar Purkinje Cell Axonal Degeneration

Area of Science:

• Veterinary Neurology
• Equine Pathology
• Neuroscience

Background:

• Shivers is a progressive equine movement disorder with unknown causes.
• Clinical signs include hind limb tremors, hyperflexed postures, and difficulty moving backward.
• The underlying neurophysiologic, pathologic, and neuroanatomic mechanisms remain unidentified.

Purpose of the Study:

• To conduct a detailed neuroanatomic and neuropathologic analysis of the sensorimotor system in horses with shivers.
• To identify the neuroanatomic locus and pathological mechanisms of equine shivers.
• To elucidate the etiology of this equine movement disorder.

Main Methods:

• Comparative neuroanatomic and neuropathologic analysis of shivers and control horses.
• Examination of skeletal muscles and peripheral nerves.
• Immunohistochemical and ultrastructural analysis of central nervous system tissues, focusing on the deep cerebellar nuclei.

Main Results:

• No abnormalities were found in hind limb, forelimb muscles, or peripheral nerves.
• Increased (80-fold) calretinin-negative, calbindin-positive, and GAD-positive axonal spheroids in Purkinje cell axons of the deep cerebellar nuclei in shivers horses.
• Presence of unusual lamellar/membranous structures resembling myelin decompaction in the deep cerebellar nuclei of shivers horses.

Conclusions:

• Shivers is characterized by end-terminal neuroaxonal degeneration in the deep cerebellar nuclei.
• This degeneration leads to context-specific hypermetria and myoclonus in affected horses.
• Provides the first identification of the neuroanatomic and neuropathologic basis of equine shivers.