ISSN 2398-2977      

Neurology: shivering

pequis

Synonym(s): Shivers


Introduction

  • A progressive chronic neuromuscular syndrome recognized for centuries.
  • Frequently seen in draft horses and warmbloods, including their crosses, characterized by a progressive inability to back up.
  • Cause: unknown but specific cerebellar pathology has been reported.
  • Signs: on forced backing, horse shows an unusual shivering or quivering of the pelvic limbs and the tail; the forelimbs may also be affected.
  • Diagnosis: history and clinical signs; lack of other neurological signs.
  • Treatment: none.
  • Prognosis: in the short-term athletic ability may be unaffected but as the condition is progressive it may eventually lead to euthanasia Euthanasia.

Pathogenesis

Etiology

  • Still obscure but research has revealed that the brains of horses with this condition are damaged in a specific area of the cerebellum. These cerebellar pathways are involved in the control of slow, learned movements such as backing or lifting a hindleg. They do not have any control over faster, natural forward gaits, which is why Shiverers can perform athletically.
  • In addition, the muscles show a significant change in fast twitch type 2x muscle fiber type similar to those horses in intensive training. Normally a horse acquires these fibers through training but, in horses with shivers, they lack cerebellar control of these fibers and they therefore become constantly active.
  • It has been shown that Shivering is characterized by abnormally elevated muscle recruitment, particularly in the biceps femoris and vastus lateralis muscles of the hindlimb during backward walking and this is associated with a selective Purkinje cell distal axonal degeneration.
  • Condition may be inherited:
    • Affected horses should not be bred from.
    • At present no specific genetic pattern has been identified.
  • It was thought initially that this condition might be related to horses having polysaccharide storage myopathy Muscle: myopathy - overview but this has recently been disproved.

Predisposing factors

General

  • Certain breeds.
  • Height of horse.
  • Geldings.

Pathophysiology

  • In one study, when compared to controls, calretinin-negative, calbindin-positive, and glutamic acid decarboxylase-positive spheroids were increased 80-fold in Purkinje cell axons within the deep cerebellar nuclei of horses with shivers.
  • Unusual lamellar or membranous structures resembling marked myelin decompaction were present between myelin sheaths of presumed Purkinje cell axons in the deep cerebellar nuclei of shivers but not control horses.
  • The immunohistochemical and ultrastructural characteristics of the lesions combined with their functional neuroanatomic distribution indicate that shivers is characterized by end-terminal neuroaxonal degeneration in the deep cerebellar nuclei, which results in context-specific hypermetria and myoclonus.

Timecourse

  • Clinical signs first apparent before 7 years of age.
  • Progressive in majority of cases.

Epidemiology

  • Young, male, greater than >17hh high, Warmblood/Draft breeds most predisposed.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Seino K K et al (2019) Three-dimensional kinematic motion analysis of Shivers in horses: a pilot study. J Equine Vet Sci 79, 13-22 PubMed.
  • Aman J E et al (2018) Abnormal locomotor muscle recruitment activity is present in horses with shivering and Purkinje cell distal axonopathy. Equine Vet J 50, 636–643 PubMed.
  • Draper A C et al (2015) Epidemiology of shivering (shivers) in horses. Equine Vet J 47 (2), 182-187 PubMed.
  • Draper A C et al (2015) Posture and movement characteristics of forward and backward walking in horses with shivering and acquired bilateral stringhalt. Equine Vet J 47, 175-181 PubMed.
  • Valberg S J et al (2015) The equine movement disorder 'Shivers' is associated with selective cerebellar Purkinje cell axonal degeneration. Vet Pathol 52 (6), 1087-1098 PubMed.

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