Clinical, histopathological and metabolic responses following exercise in Arabian horses with a history of exertional rhabdomyolysis.
Authors: McKenzie E C, Eyrich L V, Payton M E, Valberg S J
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Exertional Rhabdomyolysis in Arabian Horses Exertional rhabdomyolysis (ER) occurs with notable frequency in Arabian endurance horses, yet its underlying cause remains unclear. McKenzie and colleagues examined 10 Arabian horses with a prior ER history and 9 unaffected controls, subjecting them to a standardised 47-minute field exercise test whilst measuring plasma metabolites, creatine kinase activity, muscle glycogen concentration and cardiac response, alongside histopathological examination of gluteal muscle biopsies. Despite horses with ER showing distinctive structural changes—including internalised nuclei within mature muscle fibres, cytoplasmic glycogen and desmin aggregates, and elevated myopathic scores—their metabolic responses to exercise were indistinguishable from controls, with no differences in plasma glucose, lactate, electrolytes or muscle glycogen availability. These findings suggest that whilst Arabian horses with ER history exhibit chronic myopathic changes consistent with a structural or inflammatory myopathy, the condition does not reflect a glycogen storage disorder or primary metabolic dysfunction. For practitioners managing ER-prone Arabians, this implies that conventional conditioning protocols and metabolic support may be insufficient, and investigation should focus on inflammatory, immunological or structural factors rather than glycogen availability or electrolyte metabolism alone.
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Practical Takeaways
- •ER in Arabians appears to involve structural muscle changes rather than metabolic dysfunction, suggesting current training and conditioning protocols may not fully address the underlying myopathic condition
- •Normal metabolic responses during exercise in ER-affected horses means monitoring standard blood parameters alone is insufficient for identifying at-risk animals; histopathologic evaluation may be necessary for definitive diagnosis
- •Practitioners should consider that chronic myopathy evident on muscle biopsy may represent a predisposing factor in ER-prone Arabians, with implications for individual training tolerance and exercise progression decisions
Key Findings
- •Arabian horses with prior exertional rhabdomyolysis showed histopathologic evidence of chronic myopathy including internalized nuclei, cytoplasmic glycogen aggregates, and elevated myopathic scores despite normal muscle glycogen concentrations
- •No horses displayed clinical signs of ER during the standardized exercise test, and plasma creatine kinase increased similarly in both ER and control horses
- •Metabolic exercise responses including heart rate, plasma glucose, lactate, and electrolyte concentrations did not differ between horses with ER history and control horses
- •Findings do not support a consistent metabolic myopathy or glycogen storage disorder as the primary cause of ER in Arabian horses