Renal Lesions in Horses with Oleander (Nerium oleander) Poisoning

SIMPLE SUMMARY: Oleander (Nerium oleander) poisoning is diagnosed postmortem based on gross and microscopic changes in the heart combined with the identification of oleandrin in samples from the affected animals. Several studies in multiple mammalian species have identified microscopic lesions in the kidneys as well, although this has only been briefly mentioned in horses. In this study, we retrospectively reviewed several cases of spontaneous oleander poisoning in horses, described gross and microscopic lesions in the kidneys, and assessed the prevalence of such microscopic lesions compared with other causes of death in order to determine if they can be used as a diagnostic marker of oleander poisoning in horses. Microscopic kidney lesions were detected in horses with oleander poisoning and were similar to the changes documented in other mammalian species, although the frequency and severity were generally lower. Similar renal changes could be detected in horses that died spontaneously due to other causes or that were euthanized. We concluded that microscopic kidney lesions occur in horses with oleander poisoning, but these are not a specific diagnostic marker to differentiate it from other disease processes. ABSTRACT: A presumptive postmortem diagnosis of oleander (Nerium oleander) poisoning is made based on the histological observation of cardiomyocyte degeneration and necrosis, which is considered to be a reliable diagnostic marker, and can be confirmed via the detection of oleandrin in tissues or fluids. However, cardiac lesions may not be present in every case, and autolysis can often preclude the identification of subtle changes in the cardiomyocytes. Several studies of experimental oleander poisoning have noted the presence of renal lesions in multiple mammalian species, and case studies of accidental exposure have found similar, although more variably severe, renal abnormalities. Kidney pathology in horses with oleander poisoning has been only briefly mentioned. In this study, we reviewed 21 cases of spontaneous oleander poisoning in horses, evaluated the kidneys microscopically, and compared the renal microscopic lesions with those detected in 10 horses that died or were euthanized due to other causes to assess if histological renal changes could serve as an additional diagnostic marker for oleander poisoning in horses. We found that microscopic renal lesions, principally mild to moderate tubular changes such as hyaline cast formation, neutrophilic casts, epithelial attenuation and necrosis, as well as mineralization and congestion, occur in horses with oleander poisoning. Most of these changes match the descriptions of lesions previously noted in other species, although with less frequency and severity. Similar lesions were found in horses that died spontaneously due to different causes or were euthanized. We concluded that microscopic renal lesions may be detected in horses with oleander poisoning but they cannot be used as a diagnostic marker that allows differentiation from other disease processes or causes of death.