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  Discussion on Updated Article and seasonal pasture myopathy in horses
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Moderator:
DrO

Posted on Friday, Oct 13, 2006 - 8:33 am:

Here is a interesting study that suggests there are unknown causes of tying up on summer pasture here in the Americas and Europe. While updating the information the article on Rhabdomyolysis (tying up) and PSSM got a huge remake. Hope it makes what is a bit of a confusing mixture of interrelated diseases easier to understand, diagnose, and treat. Everytime I rewrite this article I get the urge to pull out the PSSM and EPSM topics and place them in a separate article but there continues to be strong inter-relationships between these diseases and other causes of tying up and the treatment of acute tying up episodes that keeps them together. We have updated the section on treating acute tying up episodes and expanded the section on feeding the EPSM and PSSM effected diseases.
DrO

J Am Vet Med Assoc. 2006 Oct 1;229(7):1134-41.
Seasonal pasture myopathy in horses in the midwestern United States: 14 cases (1998-2005).

Finno CJ, Valberg SJ, Wunschmann A, Murphy MJ.
Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108, USA.

OBJECTIVE: To determine clinical signs, diagnostic findings, tissue tremetone concentrations, and clinical outcome or postmortem findings in horses evaluated for acute severe nonexertional rhabdomyolysis initially attributed to white snakeroot toxicosis. DESIGN: Retrospective case series. ANIMALS: 14 horses. PROCEDURES: Records of the University of Minnesota Veterinary Medical Center or Diagnostic Laboratory were searched from 1998 to 2005. Inclusion criteria included serum creatine kinase (CK) activity > 45,000 U/L, severe nonexertional myonecrosis of proximal postural muscles at necropsy, or signs of weakness without palpably firm muscles on physical examination. Vitamin E and selenium concentrations were measured in 6 horses; tremetone concentration was measured in 7. RESULTS: Clinical signs occurred during unfavorable weather conditions. Clinical signs of generalized weakness (n = 11 horses), muscle fasciculations (10), lethargy (6), and prolonged recumbency (4) were common. Serum CK activity ranged from 46,487 to 959,499 U/L (reference range, 82 to 449 U/L), and aspartate transaminase activity was > 1,500 U/L (reference range, 162 to 316 U/L). Two horses survived with aggressive antioxidant and fluid treatment. Postmortem examination revealed acute severe myonecrosis with lipid accumulation primarily in neck, proximal forelimb and hind limb, intercostal, and diaphragm muscles. Histopathologic signs of myocardial necrosis were detected in 7 horses. Vitamin E and selenium concentrations were within reference limits. Tremetone was not detected in liver or urine samples. CONCLUSIONS AND CLINICAL RELEVANCE: Cases of rhabdomyolysis have been attributed to white snakeroot toxicosis; however, tremetone was not detected in any horses. Similarities exist between cases of seasonal pasture myopathy and cases of atypical myopathy in Europe.
Member:
Scooter

Posted on Saturday, Oct 14, 2006 - 12:15 pm:

Thanks for this article Dr.O., I find it very interesting. Could you ans. one question, what does this mean in laymans terms? Thanks

Postmortem examination revealed acute severe myonecrosis with lipid accumulation primarily in neck, proximal forelimb and hind limb, intercostal, and diaphragm muscles.

Also was this all caused by white snakeroot?
Moderator:
DrO

Posted on Monday, Oct 16, 2006 - 6:37 am:

It means there was massive muscle necrosis and they could not find evidence that white snake root was the cause.
DrO
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