Three cases of a presumptive atypical myopathy in New Zealand horses

Abstract

CASE HISTORY: Three weanling Thoroughbred fillies were presented during autumn with depression, muscle rigidity and, in one case, colic symptoms and cardiovascular shock.

CLINICAL FINDINGS: All fillies had abnormal physical examinations that included elevated heart rates and respiratory rates coupled with muscle rigidity through the back and rump. Biochemistry revealed markedly elevated creatinine kinase and aspartate aminotransferase which indicated a myopathy.

DIAGNOSIS AND TREATMENT: All three horses were diagnosed with presumptive equine atypical myopathy. The horses received supportive therapy as per the literature available at the time regarding this condition; two responded to supportive therapy and survived, and one was euthanased due to a rapid deterioration in clinical status.

PATHOLOGICAL FINDINGS: Following post mortem of one case, histology of the trapezius muscle demonstrated an acute, severe myofibre degeneration.

CLINICAL RELEVANCE: Atypical myopathy and a very similar disorder termed seasonal pasture myopathy in North America are potentially fatal, pasture-related syndromes that have been described in Europe and America but have not been previously described in New Zealand. This report describes three presumptive cases of this unique syndrome in New Zealand for the first time; it outlines the characteristics of the condition; and includes recently published information regarding diagnosis and treatment.

KEY WORDS:

• Equine
• atypical myopathy
• seasonal pasture myopathy
• New Zealand

Acknowledgements

The authors would like to thank Dr. Fauna Smith and Dr. Hannah Bowen for their notes on the patients, New Zealand Veterinary Pathology for all testing and pathology results and the stud farm for providing cases and history regarding each one.

Notes

A/G Ratio=albumin/globulin ratio; AST=aspartate aminotransferase; CK=creatinine kinase; Fib=fibrinogen; H=high; HB=haemoglobin; L=low; PCV=packed cell volume; MCH=mean cell haemoglobin; MCHC=mean cell haemoglobin concentration; MCV=mean cell volume; RBC=red blood cell; SAA=serum amyloid A; Seg Neutrophil=segmented neutrophil; WBC=white blood cell (leukocyte).