Equine atypical myopathy caused by hypoglycin A intoxication associated with ingestion of sycamore maple tree seeds.
Authors: Żuraw A, Dietert K, Kühnel S, Sander J, Klopfleisch R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Equine Atypical Myopathy and Sycamore Maple Seed Toxicity Equine atypical myopathy (EAM) — characterised by progressive muscle stiffness, recumbency and often fatal rhabdomyolysis — has long been suspected to result from ingestion of sycamore maple (*Acer pseudoplatanus*) seeds, which contain the toxic amino acid hypoglycin A (HGA). Through detailed necropsy, histopathological examination and advanced metabolite profiling via liquid chromatography-tandem mass spectrometry, Żuraw and colleagues documented a fatal case in a 2.5-year-old mare with confirmed seed ingestion, revealing severe acute muscle degeneration with pathognomonic lipid accumulation in skeletal muscle fibres alongside elevated serum and urinary acyl carnitines and acyl glycines — all metabolic markers consistent with acquired multiple acyl-CoA dehydrogenase deficiency. The findings provide compelling mechanistic evidence that HGA disrupts the β-oxidation pathway in muscle tissue, explaining the clinical presentation and tissue damage characteristic of EAM. For practitioners, this reinforces the critical importance of removing sycamore maple trees from paddocks and hay storage areas during autumn seed-fall periods, particularly in autumn-grazed pastures where horses have greatest exposure risk, and suggests that affected animals presenting with stiffness and myoglobinuria warrant urgent investigation for seed ingestion history and supportive care optimisation.
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Practical Takeaways
- •Identify and remove sycamore maple (Acer pseudoplatanus) trees from pastures where horses graze, particularly during seed fall season
- •Recognize progressive muscle stiffness, weakness, and recumbency in pastured horses as potential signs of EAM from maple seed ingestion; provide immediate veterinary evaluation
- •Educate horse owners that seeds falling from sycamore maples are toxic to horses even in small quantities; provide supplemental hay during high-risk periods rather than relying on pasture grazing near these trees
Key Findings
- •A 2.5-year-old mare with sycamore maple seed ingestion developed progressive muscle stiffness, recumbency, and fatal myopathy
- •Necropsy revealed severe rhabdomyolysis with extensive fat droplet accumulation in skeletal muscle cells of intercostal, deltoid, and trapezius muscles
- •Post-mortem metabolite analysis detected hypoglycin A metabolites and elevated acyl carnitines and acyl glycines in serum and urine
- •Findings support hypoglycin A from Acer pseudoplatanus seeds as causative agent of EAM via acquired multiple acyl-CoA dehydrogenase deficiency