A multidisciplinary diagnostic approach to pulmonary fibrosis in dogs and cats

Idiopathic pulmonary fibrosis (IPF) describes a severe, progressive, and ultimately fatal end-stage lung disorder in dogs and cats. The term IPF was coined in dogs and cats for 2 reasons: 1) the cause of the fibrosis at the time of diagnosis was unknown (i.e., presumed idiopathic); and 2) the condition was believed to resemble human IPF, the most common type of progressive fibrotic lung disease in people. However, pulmonary fibrosis in dogs and cats is not a single homogeneous disorder, does not consistently resemble all histologic features of human IPF, and is rarely exhaustively evaluated for an underlying cause. Fibrosis is a response to injury, and knowledge of the type of injury has critical implications for disease management, especially if identified before end-stage lesions occur. We offer an approach to a thorough diagnostic evaluation, including clinical, imaging, laboratory, and pathology data, which sets the stage for multidisciplinary discussions. Given that thoracic computed tomography (CT) is increasingly utilized to identify features compatible with pulmonary fibrosis in dogs and cats, we describe these CT patterns and their pitfalls. Diagnostic respiratory evaluations should investigate possible inciting causes, provide information about disease extent and severity, and identify comorbid disorders. Such evaluations will allow optimized therapy, including avoiding treatments that may have adverse effects or be overtly harmful. Importantly, although end-stage fibrotic lungs currently have no viable treatment, early recognition of known triggers of fibrosis could ultimately enable novel targeted therapy while there is still time to alter the clinical course.