A blood test has the potential to prevent prolonging the deaths of horses suffering from equine atypical myopathy, according to European researchers.
Testing the blood of horses for levels of metabolic byproducts known as acylcarnitines can provide a good indication of a horse’s chances of survival, they say.
The findings of University of Liege researcher François Boemer and his colleagues have been described in the peer-reviewed open-access journal PLOS ONE.
“We developed a scoring system to predict survival in atypical myopathy cases based on early blood sampling,” they reported.
“The scoring system proposed in this study may help clinicians with management decisions including euthanasia.”
Equine atypical myopathy, or sycamore poisoning, is caused by hypoglycin A intoxication resulting from horses eating the seeds or seedlings of certain Acer tree species, principally Acer pseudoplatanus (the sycamore maple) in Europe.
The body metabolizes the hypoglycin A, creating a characteristic blood acylcarnitine profile.
Affected horses develop acute rhabdomyolysis – muscle breakdown – that mainly affects the postural and respiratory muscles, and heart. Signs include depression, stiffness, muscle tremors, a reluctance to move, weakness, difficulty breathing and colic. Horses may have red or brown urine, a fast or irregular heart beat, and may collapse.
It has a high fatality rate, with about three-quarters of affected horses dying. The average survival time is less than two days.
Although the cause has been uncovered, no antidote currently exists.
Although supportive treatment significantly increases an animal’s chances of survival, the outcome is currently difficult to predict on initial assessment of a case.
“Medical treatment is warranted in selected cases where owners are motivated, but owners may first wish to know their horses’ chances of survival and of return to normal sport capacity,” the study team wrote.
The authors noted that current knowledge concerning prediction of survival mostly came from a major study performed at a time when the cause was unknown.
The researchers hypothesized that, although survivors and non-survivors were clinically almost similar on presentation, the outcome may be predicted early in the course of disease based on serum concentrations of acylcarnitines.
These concentrations, they said, indicated the severity of dysfunction of mitochondrial β-oxidation.
Blood samples collected from cases by the principal investigator between autumn 2006 and spring 2015 were used in the study. Serum concentrations of acylcarnitines were determined by tandem mass spectrometry.
During the study period, 51 horses were confirmed by blood analysis to have atypical myopathy. From these, 40 died or were euthanized and 11 survived.
From the results the researchers were able to develop a statistical model to accurately predict the risk of death of diseased animals, based on concentrations of three acylcarnitines (C2-Carnitine, C10:2-Carnitine and C18-Carnitine).
“The calculation of the prognosis of survival makes it possible to distinguish the horses that will survive from those that will die despite severe signs of acute rhabdomyolysis in both groups.”
Research showed that the longer a horse survived with the disease, the greater the likelihood of a positive outcome.
“The striking finding of this study is the ability to specify a prognosis based on early blood testing, at the start of the clinical examination by the practitioner or even at a sub-clinical state as shown by one horse that was sampled three hours before clinical signs became apparent.”
The horse subsequently died, which would have been predicted based on its serum levels of the three acylcarnitines. Indeed, based on the blood test, its survival chances were estimated at only 0.3%.
To date, no therapy is effective to cure atypical myopathy and care is essentially supportive, the study team noted. “Many animals die during the course of intoxication and euthanasia often appears as the ultimate veterinary’s expedient. However, some intoxicated horses survive despite a dramatic initial clinical picture.
“In this context, survival prognosis could be of critical interest to prevent euthanasia. Indeed, intensive care may be focused on animals with good survival expectancy while individuals with high death probability could be sacrificed more ‘pragmatically’ when there are signs of suffering that cannot be suppressed.”
Prognosis of survival may also be useful when testing new therapies, in order to evaluate their effectiveness.
Boemer was joined in the Belgium-based study by University of Liege colleagues Johann Detilleux, Christophe Cello and Hélène Amory; Christel Marcillaud-Pitel, from Réseau d’EpidémioSurveillance en Pathologie Equine; and Eric Richard, from the University of Normandy in France.
Boemer F, Detilleux J, Cello C, Amory H, Marcillaud-Pitel C, Richard E, et al. (2017) Acylcarnitines profile best predicts survival in horses with atypical myopathy. PLoS ONE 12(8): e0182761. https://doi.org/10.1371/journal.pone.0182761