Equis ISSN 2398-2977

Toxicity: nigropallidal encephalomalacia

Synonym(s): Yellow Star Thistle Poisoning Russian Knapweed Poisoning

Introduction

  • Cause: prolonged ingestion of Yellow Star Thistle or Russian Knapweed.
  • Incidence: usually not eaten unless poor access to forage, eg drought conditions, poor pastures or present in hay; Western USA especially in summer/autumn.
  • Signs: sudden onset of difficulty in eating and drinking with loss of weight; fixed facial expression, hypertonicity of facial muscles, moderate depression and occasional gait deficits.
  • Diagnosis: characteristic pathologic changes in brain.
  • Treatment: none known; mild cases may adapt.
  • Prognosis: guarded to hopeless.
  • Prevention: avoid exposure to toxic plants; provide adequate alternative sources of forage.

Pathogenesis

Predisposing factors

General
  • Geographical location: Western USA.
  • Season: summer and autumn.
  • Younger animals.

Specific

  • Grazing poor fields with minimal forage.

Pathophysiology

  • Ingestion of Yellow Star Thistle and/or Russian Knapweed.
  • Usually not eaten by horses except in drought conditions/poor forage/summer and autumn months/hay.
  • Unknown pathogenesis.
  • Prolonged and continuous ingestion of significant quantities of weed over weeks/months.
  • The exact pathophysiology is unknown.
  • Postulated that the plants may contain a specifically toxic substance or lack some nutritional component necessary for normal health.
  • Several sesquiterpene lactones and polyacetylenes have been isolated of unknown significance.

Timecourse

  • Prolonged and continuous ingestion over weeks/months.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Young S et al (1970)Nigropallidal encephalomalacia in horses caused by ingestion of weeds of the genus Centaurea.JAVMA157, 1602 PubMed.


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