Perspectives in veterinary medicine: Description and classification of bronchiolar disorders in cats

Reinero, Carol R.; Masseau, Isabelle; Grobman, Megan; Vientos-Plotts, Aida; Williams, Kurt

Bronchiolar disorders may result from infection, environmental or occupational exposures, immunologically mediated disease, neoplasms, chronic aspiration, and drug-induced toxicity, among other causes. [20] [21] [22] [23] Although a description of each is beyond the scope of this article, a discussion of environmental bronchiolar disorders in humans appears relevant because cats and humans share their environment and potential exposures. Known or suspected exposures causing bronchiolar disorders in humans have been reviewed 11 and include chemicals (eg, cleaning compounds, pesticides, artificial flavorings), inhalant particulates, animal or mineral dusts, and gas and smoke inhalation. Previously, environmental bronchiolar disorders were thought to be an acute sequela to a severe, overwhelming exposure, but more recently, disease with an insidious onset of clinical signs without a recognized overexposure event (perhaps representing cumulative smaller exposures) or a mild single exposure has been appreciated. 24 Injury to bronchiolar epithelial cells leads to inflammation and a fibroproliferative repair response, ultimately resulting in mural fibrosis (constrictive bronchiolitis) or intraluminal fibrosis (proliferative bronchiolitis). 25 Four histopathologic types of disease have been proposed: cellular bronchiolitis (inflammatory infiltrate of the bronchioles), constrictive bronchiolitis (concentric fibrosis of the wall leading to narrowed airway caliber), proliferative bronchiolitis (polyps of connective tissue within the bronchiolar lumen), and bronchiolitis obliterans organizing pneumonia (proliferative bronchiolitis with polyps extending into the alveolar ducts and alveoli). 11 BOX 1 The importance of the secondary pulmonary lobule in humans and the lack of an analogous structure in cats Superior imaging detail of computed tomography (CT) allows comparison with histologic features. In the human lung, an understanding of microscopic anatomy centering on the secondary pulmonary lobule is critical to make these correlations.