Renal infarcts (tissue death due to loss of blood supply) in cats are often found on ultrasonographic evaluation of the kidneys, or at necropsy. Cats are prone to these and an associated, predisposing disease process is often not found. Renal infarcts occur secondary to a thromboembolic event, and can be an incidental finding on abdominal ultrasonography performed to evaluate for either renal or nonrenal diseases. Diseases that increase the rate of thrombus formation, or that may be associated with hypercoagulability, such as hyperthyroidism, cardiomyopathy, and neoplasia, may predispose the cat to renal infarction. The lack of anastomoses between renal interlobular arteries and the high circulating blood volume the kidneys normally receive are factors that make the kidneys especially vulnerable to infarction.
This study of 600 cats evaluated with either abdominal ultrasonography, necropsy, or both, identified renal infarcts in 309 of the animals. Renal infarcts were found on ultrasonography in 191/375 cats, and on necropsy in 118/240 cats; 13 cats had both ultrasonograms and a necropsy.
Middle-aged cats (7-14 years old) were found to be 1.6 times more likely to have renal infarcts than cats under 7 years of age, but no more likely to have renal infarcts than cats over 14 years of age. A variety of breeds were represented in the study population; most cats were mixed breed (87%; 524/600). The majority of the cats were either spayed females (253/600) or neutered males (317/600). The 291 cats without renal infarcts served as time-matched controls; breed, sex and reproductive status, and age of the control group and the case group were comparable. Due to the small number of purebred cats in the study, no conclusions could be drawn regarding breed-associated renal or cardiac abnormalities.
In this study, hyperthyroidism was not significantly associated with the presence of renal infarcts. Cats with neoplasia were actually found to be less likely to have renal infarcts, but specific histopathologic diagnoses for the neoplasia were not investigated. Some types of neoplasia could be associated with hypercoagulability, while others may not be.
Significant associations between the presence of renal infarcts, cardiomyopathy, and thromboembolic disease were identified. The cats with renal infarcts were 4.5 times more likely to have hypertrophic cardiomyopathy (HCM) than those without renal infarcts. HCM and other cardiomyopathies were diagnosed in the study animals either by echocardiography or necropsy and histopathology.
Nine of the cats had a renal artery thrombus, and all of these were also diagnosed with a cardiomyopathy. All cats with a cardiac thrombus identified on ultrasonography or necropsy had renal infarcts. All cats with a thoracic limb arterial thromboembolism (ATE) found on physical examination also had renal infarcts. Cats with renal infarcts were 8.1 times more likely to have a diagnosis of distal ATE than cats without renal infarcts, and were 8.4 times more likely to have a pelvic limb ATE than cats without renal infarcts. These findings suggest that thromboembolic disease, as evidenced by the presence of a renal infarct identified sonographically, is likely to be present in cats before they have an event involving a large aortic thrombus.
Results of another study suggest that a significant number of apparently healthy cats, approximately 15%, have undiagnosed HCM. Given that the present study demonstrates that cats with renal infarcts identified ultrasonographically have a 4.5-fold greater risk of having HCM, and an 8-fold risk of a major ATE, the finding of renal infarcts on abdominal ultrasonography is a clear indication to screen a cat for HCM. In turn, early diagnosis and treatment of HCM may improve survival. [PJS]