Predicting Atypical Myopathy Survival

Hypoglycin A intake leads to atypical myopathy, but some horses can have very large quantities of the toxin in their systems and survive, while others can have very little and die, Votion said.

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By now we know that the maple sycamore tree (Acer pseudoplatanus) is the plant responsible for atypical myopathy (similar to seasonal pasture myopathy) in horses. But the same Belgian team who made that discovery is now revealing ways to test the prognosis of affected horses—and they’re finding that it has nothing to do with how much toxin the horse ingests.

“The intake of hypoglycin A in the fruits of these trees leads to atypical myopathy, but some horses can have very large quantities of the toxin in their systems and survive, whereas others can have very little and die,” said Dominique-Marie Votion, DVM, PhD, of University of Liege in Belgium. “So knowing the levels of hypoglycin A in the horse’s bloodstream alone does little good for predicting its chances of recovery.”

Votion presented her most recent work on atypical myopathy (AM) during the 2015 French Equine Research Day held March 12 in Paris.

A better prognostic tool is looking at acylcarnitines in the horse’s blood, Votion said. Acylcarnitines are essentially backlogged fat metabolites. When a horse ingests hypoglycin A, it metabolizes into a toxin that upsets the animal’s energetic metabolism—hence, the presence of the excess acylcarnitines.

Votion’s team recently validated the methodology for analyzing hypoglycin A in blood samples. They investigated samples from 18 horses admitted to the Liege Veterinary Hospital in the fall 2013 for atypical myopathy (five of which survived) and five horses admitted for exercise-induced myopathy, or exertional rhabdomyolysis—also called tying-up. They found no hypoglycin A in the exercise-induced myopathy group, nor in healthy control horses that had no access to sycamore seeds. They did find the substance in the atypical myopathy horses, but no relationship between levels and survival, Votion said. The researchers also found hypoglycin A in some healthy pasture companions of AM-affected horses, she added.

A complete biochemical profiling of energetic metabolism showed distinct differences between horses with atypical myopathy that survived and those that died, she said. Of the 34 parameters tested in the profiling, an average of 23 were outside normal limits in the survivors, while an average of 31 were outside normal limits in those that did not survive. Most telling of all were the parameters that were within normal range for the survivors but several times greater in the horses that died, Votion said.

“These parameters are really the only reliable prognostic tool that we have found so far,” Votion said. “Even behavioral signs are unreliable, as we have seen horses with relatively healthy attitudes, standing and eating comfortably for a day or two, which then dramatically deteriorate and die within hours. These horses had nonsurvival biochemical profiles from the initial diagnosis.”

But there’s a downside. Currently the biochemical profiling takes several days of laboratory testing to complete, by which time most of the horses that succumb to the disease would have already died, she said. New research should focus on developing faster biochemical profiling to help owners and caretakers make informed decisions about treatment soon after diagnosis, she said.

Meanwhile, Votion’s research group has also validated the methodology for analyzing hypoglycin A in plant extract. They looked at hypogyclin A levels in various aspects of the identified tree species, including the levels in the seeds/fruits at different periods of maturity. While more research is necessary in this area, they were able to conclude that the substance is present not only in the seeds but also in young plants (seedlings) of these species.

“Currently, there is an ongoing AM outbreak in Europe that resulted from the ingestion of these seedlings,” Votion added.

This research was funded by the Institut Français du Cheval et de l'Équitation and the University of Liège.

J.A. Habyarimana, F. Boemer, H. Amory, E. Baise, J. Carlier, P. de Tullio, C. Douny, G. Gault, P. Gustin, T. Franck, M. Frederich, C. Marcillaud-Pitel, E. Richard, F. Patarin, M. Weber, D.-M. Votion. Les nouveaux outils de diagnostic et de pronostic de la myopathie atypique. In proceedings : 41ème journée de la recherche équine, mars 2015, Paris, France, 70-74. 

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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