Atypical myopathy in Europe
Since the first cases in Belgium in autumn 2000 , the Faculty of Veterinary Medicine of Liège (FMV-ULg) is working on atypical myopathy. The definition of the clinical, pathological and epidemiological features of the disease was the first lines of work [1-3]. In 2004, the FMV-ULg has initiated an epidemiosurveillance network for atypical myopathy called AMAG (« Atypical Myopathy Alert Group » ; www.myopathieatypique.fr/en/) and supervised by Dr D. Votion. This network aims at linking scientists working on the disease. Atypical myopathy is a condition of environmental origin that kills 75% of horses within 72 hours. The network informs the equine sector of the emergence of cases so that owners of horses can take the appropriate preventive measures when clinical series are reported (usually in the fall and spring). More than a dozen European countries are now working in this network. Recently, a research group from the United States joined the network and has benefited from sera collected on European cases (more than 1000 cases have been reported to AMAG since the fall of 2006). In Belgium, the main partners are the equine clinic of the Faculty of veterinary Medicine of Liège (ULg-FMV), the Centre for Oxygen Research and Development (ULg), the European Equine Centre of Mont-le-Soie (ULg), the Department of Morphology and Pathology (FMV-ULg), the laboratory of biochemical Genetics (ULg), the laboratory of Pharmaceutical Chemistry (ULg) and the Faculty of veterinary Medicine of Ghent. Undoubtedly, veterinary practitioners are the central axis of this network and it is thanks to them that great strides have been possible in the prevention, management and treatment of cases [4-8].
From results of epidemiological studies performed on European cases [5-6] and by elucidating the pathophysiological mechanism , using several samples collected through the network, the assumption of a toxin from the environment and altering the energy metabolism has been hypothetised. Recently, Valberg and Colleagues  (see: http://onlinelibrary.wiley.com/doi/10.1111/j.2042-3306.2012.00684.x/pdf) showed that Seasonal Pasture Myopathy (SPM) in the US, which closely resembles atypical myopathy (AM) in Europe, was caused by a toxin (i.e. the toxic amino acid hypoglycin A) present in the seeds of box elder trees (Acer negundo). Once ingested, hypoglycin A is metabolized into a toxic compound (i.e. MCPA) that disrupt energetic metabolism leading to the biochemical derangements seen in both, SPM and AM.
Hypoglycin A may be contained in seeds of several trees of the genus Acer and thus could very well also be the cause of AM in Europe. In the past, botanical surveys of Belgium cases consistently reported the presence of Acer pseudoplatanus (maple tree; Aceraceae) in pastures , and moreover the contribution of trees (generally speaking) in the pathogenesis of the condition has been suggested in a recent descriptive study where trees were present at 98% of the pastures of 354 European cases .
Concerning the cause of AM in Europe, sera from European cases are being analyzed in collaboration with the University of Minnesota to search for MCPA conjugates in blood. We should know soon if AM is due to the same toxin than SPM in the US. Meanwhile, clues for diagnosis, prognosis, and preventive measures may be found in the latest studies performed on European cases [5-6].
We would like to insist on the importance of continuing reporting of European cases to the AMAG (Atypical Myopathy Alert Group; www.myopathieatypique.fr/en/). This European epidemiosurveillance system allows scientific groups that are working together on this disease to know where and when cases occur so that the data and samples that are needed for research can be collected.
So far (at the date of the 22nd October), we are not facing any outbreak (some anecdotal cases have been reported), but as you know this can change in the coming days or weeks.
The research continues since several questions remain unanswered such as:
- Why the condition is emerging while it would be due to a native plant?
- What are the factors that affect the toxicity?
- Are the Acer species the only trees causing the disease?
- How to prevent and treat the disease?
-… and many others.
Thank you for your help with the ongoing research.
1. Delguste et al., 2002. Myopathies atypiques chez les chevaux au pré: une série de cas en Belgique. Annales de Médecine Vétérinaire 2002; 146:231-243.
2. Cassart et al., 2007. Morphological alterations in oxidative muscles and mitochondrial structure associated with Equine Atypical Myopathy. Equine Veterinary Journal; http://hdl.handle.net/2268/2377
3. Votion et al., 2003. Diagnostic différentiel en cas de présomption de myopathie atypique des équidés : illustration au travers de cas référés à la Faculté de Médecine Vétérinaire de l’Université de Liège au cours du printemps 2003. Annales de Médecine Vétérinaire. http://hdl.handle.net/2268/62318
4. Votion et al., 2009. Atypical myopathy in grazing horses: A first exploratory data analysis. The Veterinary Journal. http://hdl.handle.net/2268/10009
5. van Galen et al., 2012a. European outbreaks of atypical myopathy in grazing equids (2006-2009) Part I: Spatiotemporal distribution, history and clinical features. Equine Veterinary Journal; DOI: 10.1111/j.2042-3306.2012.00556.x. http://orbi.ulg.ac.be/handle/2268/115748
6. van Galen et al., 2012b. European outbreaks of atypical myopathy in grazing equids (2006-2009) Part II: Determination of indicators for risk and prognostic factors. http://hdl.handle.net/2268/114433
7. van Galen & Votion, 2012a. Management of cases suffering from atypical myopathy:Interpretations of descriptive, epidemiological and pathophysiological findings. Part 1: First aid, cardiovascular, nutritional and digestive care. http://hdl.handle.net/2268/128066
8. Van Galen & Votion 2012b. Management of cases suffering from atypical myopathy:Interpretations of descriptive, epidemiological and pathophysiological findings. Part 2: Muscular, urinary, respiratory and hepatic care, and inflammatory/infectious status. http://hdl.handle.net/2268/128067
9. Westermann et al., 2008. Acquired multiple Acyl-CoA dehydrogenase deficiency in 10 horses with atypical myopathy. Neuromuscular Disorders. http://hdl.handle.net/2268/4440
10. Valberg et al., 2012. Seasonal Pasture Myopathy/atypical myopathy in North America associated with ingestion of Hypoglycin A within seeds of the box elder tree. Equine Veterinary Journal;
11. Votion et al., 2007. History and clinical features of atypical myopathy in horses in Belgium (2000-2005). Journal of veterinary internal Medicine. http://hdl.handle.net/2268/7594
All publications about atypical myopathy already archived on the bibliography website of the University of Liège (http://orbi.ulg.ac.be/) are available via http://orbi.ulg.ac.be/simple-search?query=atypical+myopathy.