Epidemiological, pathological and metabolomic characterisation of an acquired myopathy of dogs in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatū, New Zealand
‘Go Slow’ myopathy (GSM) is an idiopathic myopathy in dogs in New Zealand, characterised by an acute onset of trembling, weakness and collapse, followed by a prolonged period of exercise intolerance. In the first part of this thesis, the epidemiology of the disease was investigated using a telephone survey to obtain information regarding the diet, exercise, and health of affected dogs. Eighty-six confirmed cases were included in this study, and ingestion of wild pig in the week prior to the onset of clinical signs was a consistent finding (76/86 dogs; 88%; 95% confidence interval = 82 – 95%). Cases occurred most commonly in the upper North Island, particularly in Northland.
The aim of the second part of this thesis was to characterise the pathology of GSM in the same 86 dogs included in the epidemiological study, using serum biochemistry (78 dogs), histology (20 dogs), and electron microscopy (4 dogs). Acutely, affected dogs had increased serum creatine kinase and aspartate aminotransferase activities, corresponding with the histological finding of skeletal muscle degeneration in the absence of inflammation. Ultrastructural changes in skeletal muscle included mitochondrial hypertrophy, intramitochondrial inclusions and increased sarcoplasmic glycogen. Similar lesions were observed in the skeletal muscle of wild pigs from areas where GSM occurred in dogs. Affected dogs also had increased serum alanine aminotransferase activities due to accumulation of lipid and glycogen in hepatocytes. Overall, the microscopic findings were consistent with a toxic myopathy.
To further investigate the pathogenesis of the disease, liver samples were collected from 15 affected dogs and 24 clinically normal dogs for untargeted metabolic profiling using liquid chromatography-mass spectrometry. Comparison of spectra between affected and normal dogs revealed a widespread decrease in phospholipids, and increases in selected dicarboxylic acids and N-acetylated branch chain amino acids in affected dogs. No causative compounds were identified although several candidate mass spectrometric features were identified for future investigation.
Taken together, the results of these studies suggest that ‘Go Slow’ myopathy is a toxic mitochondrial myopathy in dogs that is associated with the ingestion of wild pork. The findings reported aid in the prevention, diagnosis, and management of cases, with the primary suggestion being that owners avoid feeding wild pork in areas where the myopathy occurs. Further work is required to elucidate the cause of this disease.
Material from thesis published as:
Hunt, H., Cave, N.J., Gartrell, B.D., Cogger, N., Petersen, J.A., & Roe, W.D. (2018). An epidemiological investigation of an idiopathic myopathy in hunting dogs in New Zealand, New Zealand Veterinary Journal, 66(4), 199-204. https://doi-org.ezproxy.massey.ac.nz/10.1080/00480169.2018.1464974