Identification and characterization of an idiopathic pulmonary fibrosis-like condition in cats

Reversibility of clinical and computed tomographic lesions mimicking pulmonary fibrosis in a young cat

Background

In humans with idiopathic pulmonary fibrosis (IPF), specific thoracic computed tomographic (CT) features in the correct clinical context may be used in lieu of histologic examination. Cats develop an IPF-like condition with similar features to humans. As few cats have invasive lung biopsies, CT has appeal as a surrogate diagnostic, showing features consistent with architectural remodeling supporting “end-stage lung”.

Case presentation

A 1-year-old female spayed Domestic Shorthair cat presenting with progressive respiratory clinical signs and thoracic CT changes (reticular pattern, parenchymal bands, subpleural interstitial thickening, pleural fissure thickening, subpleural lines and regions of increased attenuation with traction bronchiectasis and architectural distortion) consistent with reports of IPF was given a grave prognosis for long-term survival. The cat was treated with prednisolone, fenbendazole, pradofloxacin and clindamycin. Five months later, while still receiving an anti-inflammatory dose of prednisolone, the cat was re-evaluated with owner-reported absent respiratory clinical signs. Thoracic CT demonstrated resolution of lung patterns consistent with fibrosis.

Conclusions

Fibrotic lung disease is irreversible. Despite this cat having compatible progressive respiratory signs and associated lung patterns on thoracic CT scan, these abnormalities resolved with non-specific therapy and time, negating the possibility of IPF. While the cause of the distinct CT lesions that ultimately resolved was not determined, infection was suspected. Experimental Toxocara cati infection shows overlapping CT features as this cat and is considered a treatable disease. Improvement of CT lesions months after experimental heartworm-associated respiratory disease in cats has been documented. Reversibility of lesions suggests inflammation rather than fibrosis was the cause of the thoracic CT lesions. This cat serves as a lesson that although thoracic CT has been advocated as a surrogate for histopathology in people with IPF, additional studies in cats are needed to integrate CT findings with signalment, other clinicopathologic features and therapeutic response before providing a diagnosis or prognosis of fibrotic lung disease.

Clinical, computed tomographic and histopathological findings in two cats with pulmonary fibrosis of unknown aetiology

Case series summary

Two cats were presented for further investigation of respiratory signs. One cat had a history of a cough and the other, tachypnoea. In each case, thoracic CT was performed, which revealed a generalised marked reticular pattern in the first cat and focal consolidation of the right caudal lung lobe in the second cat. The first cat was euthanased following completion of the imaging study and a post-mortem examination was performed. The second cat underwent surgical excision of the abnormal lung lobe and survived for 4 years after diagnosis. Histopathology performed on lung tissue removed from each cat was consistent with pulmonary fibrosis.

Relevance and novel information

This small case series adds to the existing literature and highlights the heterogeneous clinical course and variable appearance of pulmonary fibrosis on CT of affected cats. These cases provide evidence that pulmonary fibrosis in cats incorporates a wide spectrum of fibrotic lung disease and demonstrates the possibility for prolonged survival following diagnosis where disease is localised and amenable to surgical resection.

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

This Perspectives in Veterinary Medicine article seeks to define, describe putative causes, and discuss key diagnostic tests for primary and secondary bronchiolar disorders to propose a classification scheme in cats with support from a literature review and case examples. The small airways (bronchioles with inner diameters <2 mm), located at the transitional zone between larger conducting airways and the pulmonary acinus, have been overlooked as major contributors to clinical syndromes of respiratory disease in cats. Because the trigger for many bronchiolar disorders is environmental and humans live in a shared environment with similar susceptibility, understanding these diseases in pet cats has relevance to One Health. Thoracic radiography, the major imaging modality used in the diagnostic evaluation of respiratory disease in cats, has low utility in detection of bronchiolar disease. Computed tomography (CT) with paired inspiratory and expiratory scans can detect pathology centered on small airways. In humans, treatment of bronchiolar disorders is not well established because of heterogeneous presentations and often late definitive diagnosis. A review of the human and veterinary medical literature will serve as the basis for a proposed classification scheme in cats. A case series of cats with CT or histopathologic evidence of bronchiolar lesions or both, either as a primary disorder or secondary to extension from large airway disease or interstitial lung disease, will be presented. Future multi‐institutional and multidisciplinary discussions among clinicians, radiologists, and pathologists will help refine and develop this classification scheme to promote early and specific recognition and optimize treatment.

Animal models of fibrotic lung disease

Interstitial lung fibrosis can develop as a consequence of occupational or medical exposure, as a result of genetic defects, and after trauma or acute lung injury leading to fibroproliferative acute respiratory distress syndrome, or it can develop in an idiopathic manner. The pathogenesis of each form of lung fibrosis remains poorly understood. They each result in a progressive loss of lung function with increasing dyspnea, and most forms ultimately result in mortality. To better understand the pathogenesis of lung fibrotic disorders, multiple animal models have been developed. This review summarizes the common and emerging models of lung fibrosis to highlight their usefulness in understanding the cell-cell and soluble mediator interactions that drive fibrotic responses. Recent advances have allowed for the development of models to study targeted injuries of Type II alveolar epithelial cells, fibroblastic autonomous effects, and targeted genetic defects. Repetitive dosing in some models has more closely mimicked the pathology of human fibrotic lung disease. We also have a much better understanding of the fact that the aged lung has increased susceptibility to fibrosis. Each of the models reviewed in this report offers a powerful tool for studying some aspect of fibrotic lung disease.

Computed tomography imaging of a leopard tortoise (Geochelone pardalis pardalis) with confirmed pulmonary fibrosis: a case report

An approximately 20-year-old, female Leopard tortoise (Geochelone pardalis pardalis) was presented with dypsnea, wheezing, anorexia and depression. Whole body radiographs revealed generalized diffuse unstructured ‘interstitial lung pattern’ with thickened pulmonary septae while computed tomography (CT) showed emphysematous lung parenchyma and thickened pulmonary septae bordered by irregular ground-glass opacity with smaller areas of ‘honeycombing’. These imaging findings together with histopathologic findings were compatible with chronic, extensive ‘interstitial’ pulmonary fibrosis.

Modulation of lung inflammation by the Epstein-Barr virus protein Zta

Several studies have implicated gamma-herpesviruses, particularly Epstein-Barr virus (EBV), in the progression of idiopathic pulmonary fibrosis. The data presented here examine the possible role that EBV plays in the potentiation of this disease by evaluating the pulmonary response to expression of the EBV lytic transactivator protein Zta. Expression of Zta in the lungs of mice via adenovirus-mediated delivery (Adv-Zta) produced profibrogenic inflammation that appeared most pronounced by day 7 postexposure. Relative to mice exposed to control GFP-expressing adenovirus (Adv-GFP), mice exposed to Adv-Zta displayed evidence of lung injury and a large increase in inflammatory cells, predominantly neutrophils, recovered by bronchoalveolar lavage (BAL). Cytokine and mRNA profiling of the BAL fluid and cells recovered from Adv-Zta-treated mice revealed a Th2 and Th17 bias. mRNA profiles from Adv-Zta-infected lung epithelial cells revealed consistent induction of mRNAs encoding Th2 cytokines. Coexpression in transient assays of wild-type Zta, but not a DNA-binding-defective mutant Zta, activated expression of the IL-13 promoter in lung epithelial cells, and detection of IL-13 in Adv-Zta-treated mice correlated with expression of Zta. Induction of Th2 cytokines in Zta-expressing mice corresponded with alternative activation of macrophages. In cell culture and in mice, Zta repressed lung epithelial cell markers. Despite the profibrogenic character at day 7, the inflammation resolves by 28 days postexposure to Adv-Zta without evidence of fibrosis. These observations indicate that the EBV lytic transactivator protein Zta displays activity consistent with a pathogenic role in pulmonary fibrosis associated with herpesvirus infection.

Aetiology and outcome in 90 cats presenting with dyspnoea in a referral population

Objectives:Dyspnoea is an unspecific severe presenting sign, which can be life threatening and requires prompt treatment. Dyspnoeic cats often have significant underlying disease. Underlying aetiologies in cats that presented with dyspnoea were reviewed, and associations with patient signalment and outcome were investigated.

Methods:The case records of 90 dyspnoeic cats were retrospectively reviewed and separated into different groups depending on aetiology (cardiac, respiratory, neoplastic and trauma). Duration of clinical signs, presentation, hospitalisation length and survival were analysed.

Results:Cardiac (38 per cent), respiratory (32 per cent) and neoplastic (20 per cent) diseases were common causes of feline dyspnoea. Cats with respiratory causes had longer duration of clinical signs (P<0·001) before presentation. Cats with neoplasia were significantly older (P<0·001). No significant difference in respiratory rates was present between the groups (P = 0·154). High heart rates (P<0·001) and abnormalities on cardiac auscultation were more likely in the cardiac group.

Clinical Significance:Frequent causes of dyspnoea in cats were cardiac disease followed by respiratory causes and neoplastic conditions. Heart rate on presentation and presence of heart murmurs or gallops are useful to identify cardiac causes. Improved proportion surviving was found in the respiratory group (P = 0·027), whereas cats with neoplasia had the worst outcome.