Renal dysplasi hos engelsk cocker spaniel

Sammanfattning: Renal dysplasi (RD) is a congenital chronic renal disease affecting young dogs. It is a rather common disease that occurs in a large number of dogs and in some breeds there is a familiar incidence or suspected hereditary background. Both the etiology and pathogenesis are still unknown, but a theory about the cause of RD is that the two components that form the kidney, the uretheric bud and the metanephrogenic blastema, don´t interact normally in the embryo. Kidneys affected by RD contain fetal (immature) structures that are inappropriate for the state of development/age of the dog and abnormal structures caused by an abnormal differentiation. Affected dogs usually are under <2 years old and show clinical signs of chronic renal failure. There is no treatment, but dogs with RD usually die or are put to death after that signs have developed. Diagnosis is made by histopathology and the primary changes that may be seen are fetal glomeruli / tubuli, atypical tubular epithelium, persistent mesenchyme, persistent metanephric ducts and dysontogenic metaplasia. In Sweden there is a control program with central registration at SKK (Swedish Kennel Club) of all diagnosed cases of RD within the breed English cocker spaniel. In addition to RD another congenital renal disease, hereditary nephropathy (HN), has been recognized in the English cocker spaniel. Like RD, HD affects young dogs. In contrast to RD, it has been shown that HN is caused of a mutation in the gene COL4A4, which confers a defect in collagen IV, an essential component of glomerular basement membranes (GBM). The mode of inheritance of the mutation is autosomal recessive. The defective collagen provides a multilaminar, longitudinal division of the GBM, leading to protein leakage in the glomeruli. Affected dogs develop proteinuria at an early stage and usually show signs of chronic renal failure before 2 years of age. In contrast, proteinuria is not typical of RD. Currently, there is no description of the histopathological picture of RD in the English cocker spaniel, but such a description is important for accurate diagnosis and for the control program to function properly. The purpose of this study was to describe the typical histopathological changes and the clinical picture of RD in the English cocker spaniel. The study was based on histological sections from archival kidney tissue from 21 English cocker spaniels that had been diagnosed with RD or juvenile progressive nephropathy (PNP) during the period 1987-2007. Set criteria for the dog that would be included in the study were, age <2 years and typical histopathological signs of RD and 14 dogs fulfilled these criteria. These dogs were used to describe the typical histopathological picture using light microscope. The clinical signs and macroscopic picture were described based on information from the dogs' referrals. Three of the excluded dogs, all <2 years, showed signs of glomerulonephritis, which gave a suspicion of HN. The histopathological picture in HN, however, is non-specific and the diagnosis must be verified with electron microscopy, which was not possible to perform on the existing material. The 14 selected dogs showed clinical signs typical of chronic renal failure, the most common signs being polyuria / polydipsia, vomiting, azotemia and anemia. The macroscopic picture characterized by small and irregular kidneys. The most common primary histopathological changes were fetal glomeruli (79%) and atypical tubular epithelium of adenomatoid type (57%). Persistent mesenchyme and persistent metanephric ducts were present in, 29% and 14% of the dogs, respectively. Persistent mesenchyme was always accompanied by any one of the other changes, whereas fetal glomeruli, atypical tubular epithelium and persistent metanephric ducts were present both as single entities and together with other changes. Fetal tubules and dysontogenic metaplasia were not seen in any of the dogs. Fetal glomeruli and atypical tubular epithelium are the most common changes of RD in other breeds and the histopathological picture of the English cocker spaniel is most similar to the one seen in Flatcoated Retriever. The final conclusions of this study are that the main histopathological criteria for RD within the English cocker spaniel are the presence of fetal glomeruli and atypical tubular epithelium of the adenomatoid type. Persistent mesenchyme and persistent metanephric ducts are of less importance for the diagnosis of RD in the English cocker spaniel, but their presence together with other primary changes further evidencing the histopathological diagnosis.