Atypical myopathy

Atypical myopathy is a pasture-associated syndrome characterised by the sudden onset of acute rhabdomyolysis apart from any exercise. This frequently fatal acquired condition is intimately linked with the environment. Atypical myopathy occurs primarily in autumn in Europe and Midwestern United States (Finno et al. 2006) (van Galen et al. 2011a) but outbreaks have also been reported in spring (Votion et al 2003; van Galen et al. 2011a). Atypical myopathy appears to be specific to horses and to the author’s knowledge no other grazing livestock has been confirmed for the disease. In recent years, atypical myopathy has been recognized as an emergent disease (Votion and Serteyn 2008; van Galen et al. 2010).

Lately, major advances have been made in the understanding of the pathophysiology of the condition (Cassart et al. 2007; van der Kolk et al. 2010) and causative hypothesis (Unger-Torroledo et al. 2010). The metabolic defect occurring in atypical myopathy affected horses is a multiple acyl-CoA dehydrogenase deficiency (MADD), which affects mitochondrial fatty acid energy metabolism but not the use of carbohydrates for energy supply (van Galen et al. 2008; Westermann et al. 2008). The development of atypical myopathy is probably multifactorial but the condition has been associated with Clostridium sordellii lethal toxin (Unger-Torroledo et al. 2010). However, no specific treatment of the condition exists and the most effective way of controlling the disease is prevention that includes specific management practices at the horse and pasture levels. This review summarises the latest knowledge about atypical myopathy and provides practical information to prevent the disease.