Nasal histological findings in asymptomatic control dogs and in dogs with chronic inflammatory rhinitis

Chronic inflammatory rhinitis (CIR) is among the most common causes of chronic nasal signs in dogs. Despite research efforts, the etiology of CIR remains mostly undiscovered. The aim of our study was to describe the histological findings in nasal biopsies of control dogs without signs of nasal disease compared to dogs with CIR. The study groups were control dogs euthanized for reasons unrelated to this study (<i>n</i> = 20) and previously collected, archived nasal biopsies from dogs diagnosed with CIR (<i>n</i> = 20). A CIR diagnosis was based on clinical presentation, computed tomography, rhinoscopy, and histopathological findings indicative of CIR. Inflammatory cell counts and changes in the mucosal epithelium and associated lamina propria were evaluated from nasal biopsy specimens. The numbers of lymphocytes and plasma cells (<i>P</i> < .0001), neutrophils (<i>P</i> < .0001), and eosinophils (<i>P</i> = .0016) in the lamina propria, and mucosal intraepithelial leukocytes (<i>P</i> < .0001) were significantly higher in dogs with CIR compared to control dogs. A small population of leukocytes was also observed in control dogs, likely representing a physiological immune cell population. The type of inflammation in CIR is not purely lymphoplasmacytic, as both neutrophils and eosinophils were also detected in CIR dogs. The mucosal epithelium was thicker (<i>P</i> = .006), and visible goblet cells (<i>P</i> < .001) were decreased, in dogs with CIR, with a multifocal loss of cilia in some dogs, which may represent a form of respiratory epithelial metaplasia. Epithelial alterations likely play a role in the pathophysiology of CIR and contribute to the clinical signs.