Causes of sudden unexpected death in dogs and cats – it’s not the neighbour!

Margaret Stalker

Animal Health Laboratory, University of Guelph, ON

AHL Newsletter 2019;23(4):16-17.

There are few things more traumatic for a pet owner than witnessing the completely unexpected death of a family pet, or finding a pet lying dead in the home, yard or neighborhood. Determining the cause of sudden unexpected death is one of the main reasons companion animals are submitted to the Animal Health Laboratory for postmortem examination. Perhaps not surprisingly, the history often includes the owner’s query if this could be a case of malicious poisoning, particularly for animals with access to the outdoors. Thankfully, this scenario appears to be the notable exception, rather than the rule. As part of the OAHN Companion Animal disease surveillance network, causes of sudden unexpected death or animals found dead were tabulated from Sept 2015 to Sept 2019. Sudden death was defined as unexpected death occurring in less than 1 hour with no observed or recognized antecedent clinical signs.

For dogs (n =150 cases), the most frequent cause of death was underlying occult neoplasia (42 cases). The majority of these were hemangiosarcoma (33 cases), often with catastrophic pericardial, thoracic or abdominal hemorrhage as the cause of death. Cardiac disease was the second most frequent diagnosis (36 cases), including various forms of cardiomyopathy, and 4 cases of congenital aortic stenosis. Respiratory disease (16 cases including 9 cases of acute onset choking/asphyxia due to aspirated food), gastrointestinal accidents (11 cases including 9 cases of gastric dilation/volvulus and 2 cases of gastrointestinal foreign bodies with perforation), and trauma (14 cases including suspected motor vehicle trauma and 1 likely predator attack) were also common causes of unexpected death. Two cases of acute pancreatic necrosis, 10 cases of miscellaneous infectious diseases (including septicemia, pyelonephritis and hemolytic anemia due to Babesia canis infection), and 3 cases of miscellaneous inflammatory conditions (including idiopathic hemorrhagic enterocolitis and exertional rhabdomyolysis) were diagnosed, as well as a single case of juvenile Addison’s disease. There was a single case of chocolate toxicosis and a single case of bromodiolone toxicosis, as well as 5 additional cases of suspected anticoagulant rodenticide toxicity. Note that a definitive diagnosis was sometimes not reached due to limitations in the amount of testing allowed by the owner for various reasons. In 8 cases, no detectable lesions or cause of death was found.

For cats (n = 71 cases), the most frequent cause of death was underlying cardiac disease (44 cases), the majority of which were various forms of cardiomyopathy (42 cases). Trauma (including presumed predator attack), miscellaneous inflammatory conditions (ranging from anaphylaxis to chronic cholangiohepatitis with sepsis), and cases with no detectable lesions or cause of death each accounted for 6 cases, while miscellaneous infectious conditions (including panleukopenia, Salmonella typhimurium sepsis and cerebral cuterebriasis) accounted for 5 cases. Neoplasia (2 cases) and urethral obstruction/FLUTD (2 cases) were the least frequent diagnoses, the reverse of the trend in the dog population where neoplasia was the most frequent diagnosis.

While this list is likely not surprising to the experienced practitioner, it underscores the utility of postmortem examination in these highly emotional cases, and can help owners come to a place of closure without lingering suspicions of foul play.