Clinical, histopathologic, cystoscopic, and fluorescence in situ hybridization analysis of proliferative urethritis in 22 dogs

Background Proliferative urethritis (PU) is a lower urinary tract disease of dogs characterized by frond‐like lesions in the urethra. The etiology of PU is unknown, although an association with bacterial cystitis is reported. Objectives Deep‐seated bacterial cystitis is associated with PU, particularly in dogs with neutrophilic or granulomatous inflammation. Animals Twenty‐two client‐owned dogs with PU and 5 control dogs euthanized for non‐urinary disease. Methods In retrospective analysis, medical records of dogs with PU from 1986 to 2016 were reviewed. Signalment, clinical signs, cystoscopic findings, antimicrobial use, and results of urine, bladder, or urethral tissue cultures, if available, were recorded. Histopathology was reviewed and classified as lymphocytic‐plasmacytic (LP), neutrophilic, LP‐neutrophilic (LPN), granulomatous, or pleocellular. Eubacterial fluorescence in situ hybridization (FISH) was performed on 18 tissue samples (13 cases, 5 controls), with subsequent evaluation of bacterial species. Results Of the 22 dogs, 9 had LP urethritis, 6 had LPN, 4 had pleocellular, and 3 had neutrophilic urethritis. Of note, 7 of 13 PU samples were FISH+ for adherent or invasive bacteria; 1 of 5 controls were FISH+ for adherent bacteria. Five dogs had negative urine and tissue cultures when FISH was positive. There was no association detected between the type of urethral inflammation and the results of urine and tissue culture or FISH. Conclusions and Clinical Importance The type of inflammation varied widely in these 22 PU cases. Deep‐seated bacterial urethritis could be contributing to the inflammatory process in some dogs, regardless of the inflammation type. Urine and tissue cultures likely underestimate bacterial colonization of the urethra in dogs.