Unilateral pyelonephritis with encapsulated structure in a dog.

A young female Golden Retriever with a portosystemic shunt presented with hypoalbuminemia, hyperammonemia, and severe ascites, ultimately succumbing to the illness. Necropsy revealed renal papillary necrosis in the right renal pelvis. Histological examination identified an encapsulated structure within the renal pelvis containing basophilic granules surrounded by an eosinophilic, multilayered capsule. Mass spectrometry analysis of the encapsulated structure identified predominant Staphylococcus pseudintermedius-specific proteins. This finding was further confirmed by PCR and immunohistochemistry, establishing an infection caused by Staphylococcus spp. This is the first documented case of papillary necrosis with an encapsulated structure as a severe manifestation of pyelonephritis associated with S. pseudintermedius.