Equine rhabdomyolysis.
Authors: Quist E M, Dougherty J J, Chaffin M K, Porter B F
Journal: Veterinary pathology
Summary
# Editorial Summary: Equine Rhabdomyolysis This case report examines a 1.5-year-old Quarter Horse presenting with acute muscular deterioration secondary to severe bilateral guttural pouch empyema caused by *Streptococcus equi* subsp. *equi*, highlighting the diagnostic challenge of distinguishing between primary myopathic conditions and secondary rhabdomyolysis triggered by systemic infection. Clinical presentation included chronic nasal discharge, elevated white cell counts, progressive lethargy and myalgia that rapidly progressed to recumbency; post-mortem examination revealed extensive bilateral muscle pallor across all major muscle groups consistent with severe myonecrosis. PCR confirmation of *S. equi* infection in the purulent guttural pouch exudate supported an immune-mediated mechanism of muscle damage rather than direct toxaemia or septicaemia. The case underscores that equine myopathies remain poorly characterised conditions with overlapping clinical presentations, and that practitioners must consider secondary myopathy arising from chronic bacterial infections alongside primary myodegenerative and metabolic differentials when evaluating horses with acute muscular pain and weakness. Understanding these complex aetiological relationships is essential for improving diagnostic accuracy and informing prognosis in cases of rhabdomyolysis.
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Practical Takeaways
- •Acute muscular pain and weakness with recumbency in young horses warrants urgent investigation of systemic infections such as guttural pouch empyema, as secondary immune-mediated rhabdomyolysis can develop rapidly
- •Streptococcus equi infection should be considered in differential diagnosis of equine myopathy, particularly when concurrent upper respiratory signs are present
- •Rhabdomyolysis has multiple poorly understood etiologies—systematic diagnostic work-up including infectious screening is essential before euthanasia decisions
Key Findings
- •Severe bilateral guttural pouch empyema with S. equi infection presented concurrently with acute rhabdomyolysis in a 1.5-year-old Quarter Horse gelding
- •Widespread pallor in skeletal muscles across all major muscle groups was observed at necropsy
- •S. equi-associated immune-mediated rhabdomyolysis was identified as the most likely mechanism in this case