<i>Escherichia coli</i> –associated renal malakoplakia in 2 dogs

Malakoplakia is an uncommon granulomatous disease reported to affect mainly the urinary bladder and, less frequently, the urogenital tract, gastrointestinal tract, and lymph nodes. We describe cases of malakoplakia within the renal medulla of 2 dogs. Both dogs had a history of recurrent urinary tract infections with urine culture growth of <i>Escherichia coli</i>. Autopsy findings in dog 1 included ~60 tan-to-yellow, irregular nodules within the renal medulla, and tan-to-red, semi-firm nodules within the urinary bladder mucosa. Dog 2 had no gross changes within the kidneys but rather had ~20 red, semi-firm nodules along the surface of the apex of the urinary bladder. Histologically, the renal medulla of both dogs had sheets of foamy IBA1-positive macrophages with cytoplasmic granules and inclusions of intensely periodic acid-Schiff (PAS)-positive and occasional intracytoplasmic von Kossa- and Prussian blue-positive Michaelis-Gutmann bodies, consistent with malakoplakia. Fluorescence in situ hybridization and/or immunohistochemistry confirmed <i>E. coli</i> within macrophages. An underlying endocrinopathy could be a predisposing factor in the development of malakoplakia in older dogs.