Seasonal Pasture Myopathy

Thursday, December 5, 2019

Hypoglycin A Toxicosis - Equine (NY) – An adult miniature horse mare from northern New York presented for dullness, choke and dysphagia with marked elevation in muscle enzymes, and was diagnosed with seasonal pasture myopathy (SPM). SPM is caused by ingestion of the toxin hypoglycin A in the seeds of the box elder tree (Acer negundo). Hypoglycin A ingestion results in a lipid storage myopathy due to deficiency in skeletal muscle acyl-CoA dehydrogenase (MADD). The mare in this case had confirmed exposure to box elder seeds in her pasture. While dysphagia and choke are reported clinical sign of SPM, these cases more classically present with dramatic weakness and difficulty standing, progressing to difficulty breathing and ultimately recumbency. Muscle enzymes (CK and AST) are typically markedly elevated in SPM cases, with associated myoglobinuria. While there is no commercial assay for measuring hypoglycin A available in the United States, cases can be diagnosed based upon accumulation of abnormally high levels of acylcarnitines in the blood and organic acids in the urine.  SPM is fatal in the majority of cases. For additional photos of box elder and their seeds and further information on SPM, click here.