Fibrose renal associada à necrose tubular aguda em cães e gatos: revisão histológica, estadiamento e dados retrospectivos

Abstract

The kidneys play an essential role in sustaining life and are frequently involved in the causes of death and euthanasia in dogs and cats. In cases of acute kidney injuries, surviving animals are expected to undergo regeneration or repair processes through fibrosis. In this context, this thesis presents a retrospective analysis of the histopathological changes related to fibrosis found in the kidneys of dogs and cats diagnosed with acute tubular necrosis (ATN), the main acute renal alteration observed in dogs and cats treated at the Veterinary Oncology Service of the Federal University of Pelotas (SOVET-UFPEL) between 2016 and 2024. The data are presented in two articles: The first article describes the histological changes and proposes a grading system for acute tubular necrosis (ATN), while the second presents a comparative analysis between the proposed ATN grading system and other existing systems. For the first article, renal samples from dogs and cats with ATN were analyzed, obtained through data from the integrated SIG/SOVET system, and classified as ischemic or nephrotoxic ATN. Two control groups included kidneys from animals with chronic kidney disease (positive control) and kidneys without alterations (negative control). The ATN grading was based on data obtained from histological slides stained with hematoxylin and eosin, considering epithelial necrosis, pigmented casts, and peritubular fibrosis. A scoring system from 0 to 3 was used, classifying ATN as mild (≤3), moderate (>3 - ≤6), and severe (≥7). Fibrosis was assessed using Masson's trichrome stain regarding intensity and distribution in three renal regions. Epidemiological data (species, breed, age, sex, and etiology) were collected from SIG/SOVET and SimplesVet®, classifying animals by age group: puppies (<1 year), adults (1-9 years), and seniors (>9 years). As a result of the first article, a direct correlation was observed between the severity of histological changes and the intensity of peritubular fibrosis, suggesting its early role in the fibroplastic response of ATN. The ATN grading showed a higher frequency of grade II in felines (62.5%) and a balanced distribution between grades II and III in dogs. Fibrosis ranged from mild to severe in both groups, highlighting the need for further studies focused on the histological diagnosis of ATN. The second article, using the same platforms as the first, crossreferenced the animals’ data and the staging of the alterations with serum urea and creatinine levels. The results showed discrepancies between the grading systems, indicating that serum creatinine may be a late marker for diagnosing ATN and acute kidney injury (AKI).