Chronic idiopathic myopathy in Icelandic horses: A case series.
Authors: Hansen Sanni, Hopster-Iversen Charlotte, Berg Lise, Fjeldborg Julie, Massey Claire, Piercy Richard J, Carstensen Helena
Journal: Equine veterinary journal
Summary
# Editorial Summary: Chronic Idiopathic Myopathy in Icelandic Horses Poor performance and multi-limb lameness in Icelandic horses have lacked a clear aetiological explanation, despite exertional myopathies being recognised causes of reduced athletic function in other equine populations. Hansen and colleagues investigated 17 Icelandic horses with performance issues by measuring resting and post-exercise serum creatine kinase (CK) activity and examining semimembranosus muscle biopsies to identify histopathological changes. Twelve horses (71%) showed non-specific muscle degeneration and regeneration consistent with myopathy, and these affected horses demonstrated significantly elevated post-exercise CK activity (median 1637 U/L versus 234 U/L in normal horses, p = 0.02), though clinical signs such as tachypnoea, fatigue and reluctance to perform tölt or canter were not uniformly predictive of myopathy status. The findings suggest a breed-specific myopathy distinct from other recognised equine exertional disorders; practitioners should now consider myopathy investigation in Icelandic horses presenting with decreased performance, multi-limb lameness, or abnormal serum CK responses to work, using post-exercise CK measurement as a useful screening tool to guide further diagnostic muscle biopsy when indicated.
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Practical Takeaways
- •In Icelandic horses presenting with poor performance and/or multi-limb lameness, consider underlying myopathy and measure resting and post-exercise serum CK activity as a screening tool
- •Muscle biopsy of the semimembranosus may be warranted when CK elevation is documented, as clinical signs alone cannot distinguish affected from unaffected horses
- •Exercise intolerance and gait abnormalities in this breed warrant investigation beyond lameness diagnostics, as a breed-specific myopathy appears to be emerging
Key Findings
- •12 of 17 Icelandic horses (71%) demonstrated non-specific histological features of muscle degeneration and regeneration consistent with myopathy
- •Horses with myopathy had significantly higher post-exercise CK activity (median 1637 U/L) compared to normal muscle group (median 234 U/L, p=0.02)
- •Clinical phenotypic traits including tachypnoea, fatigue, stumbling and reluctance to tölt or canter were present in both affected and unaffected horses
- •A novel myopathy in Icelandic horses is suggested, distinct from previously characterized equine exertional myopathies