Presumptive Development of Fibrotic Lung Disease From Bordetella bronchiseptica and Post-infectious Bronchiolitis Obliterans in a Dog

Constrictive bronchiolitis obliterans with a presumptive etiology of preceding feline herpesvirus infection in a cat

Background

Bronchiolar disorders are rarely recognized in cats. Constrictive bronchiolitis obliterans is characterized by concentric peribronchiolar fibrosis and inflammation of the bronchioles, but the underlying causes remain poorly understood in current small animal medicine.

Case presentation

A 9-year-old cat presented with paroxysmal tachypnea, infrequent cough and persistent labor breathing. Thoracic radiography showed lung hyperinflation and bronchointerstitial pattern, and pulmonary function assessment revealed flow limitation in the late-expiratory phase and poor response to short-acting bronchodilator. Dorsally distributed subpleural ground glass opacities with distinct margin and tree-in-bud opacities were observed on lung high-resolution computed tomography. The cat underwent bronchoalveolar lavage (BAL) and showed severe neutrophilic inflammation. Feline herpesvirus was the only pathogen detected in the BAL fluid. Multiple therapeutic attempts were unsuccessful and the cat died 8 weeks after the initial presentation. Necropsy revealed the infiltration of inflammatory cells, obstruction of the bronchiolar lumen, and submucosal concentric fibrosis suggesting constrictive bronchiolitis obliterans. Combining the pre- and post-mortem findings, as well as the time from symptom onset or BAL to necropsy, constrictive bronchiolitis obliterans was possibly triggered by a preceding feline herpesvirus infection in this case.

Conclusions

The history of nonvaccinated status, lower airway neutrophilic inflammation, and presence of feline herpesvirus in the BAL fluid without coexistence of other pathogens led to the presumption that constrictive bronchiolitis obliterans was induced by a preceding feline herpesvirus infection in this cat. The pathological changes of bronchiolitis obliterans induced by a preceding feline herpesvirus infection could be different from that of cats with acute herpesvirus pneumonia, such as intranuclear inclusions would disappear over time and were no longer found 7–10 days after inoculation. The presence of patchy distribution of subpleural ground glass opacities on lung high-resolution computed tomography should raise the suspicion of peribronchiolar fibrosis. Clinical awareness of bronchiolar disorders as a differential diagnosis is important in cats with lung hyperinflation and labored breathing who show poor reversibility to bronchodilator.

Lower airway collapse: Revisiting the definition and clinicopathologic features of canine bronchomalacia

Bronchomalacia (BM) is an inconsistently defined term in dogs, impairing understanding of clinical presentation, therapeutic response and prognosis. Herein the authors propose to clarify the definition of canine bronchomalacia (CBM) as regional to diffuse dynamic airway collapse of segmental and/or subsegmental bronchi with associated clinical signs due to airflow limitation. In contrast to tracheal collapse, mainstem bronchial collapse, and in some cases lobar collapse, CBM requires advanced imaging. Common co-morbid conditions (e.g., chronic bronchitis, mitral valve degenerative disease, etc.) should be identified during a comprehensive diagnostic evaluation. Current empiric treatments advocated in absence of clinical trials documenting efficacy in the dog warrant evaluation, as some (e.g., bronchodilators) may have detrimental effects in certain types of airway collapse in humans. There is no direct treatment for CBM, as defined above, but non-specific therapies and targeted treatment of co-morbid disease may improve clinical signs and quality of life. In this manuscript, the authors provide a review of the different types of airway collapse focusing on CBM, reviewing their definition and etiology, proposing a classification scheme, and discussing clinical signs, diagnostic testing, and treatment. Future studies should focus on both improving understanding of the etiology and natural disease progression of CBM and treatment trials.

Risk Factors and Outcomes in Dogs With Respiratory Disease Undergoing Diagnostic Airway Lavage

Advanced diagnostic testing is becoming increasingly important to accurately assess pulmonary parenchymal, airway, and pulmonary vascular diseases in dogs. Due to respiratory system compromise, diagnostic procedures performed under general anesthesia, including thoracic computed tomography (CT) and bronchoalveolar lavage (BAL), are thought to carry significant risk to dogs with respiratory disease. In lieu of performing these diagnostics, empirical medical therapy is often administered, potentially delaying appropriate therapy or providing unnecessary treatment. This study prospectively evaluated risk factors and outcomes for dogs with respiratory disease undergoing general anesthesia for thoracic CT and BAL. Arterial blood gas samples were taken pre- and post-BAL to evaluate pulmonary gas exchange. Pre-BAL arterial partial pressure of oxygen-to-fractional inspired oxygen ratio was used to stratify dogs into groups of mild or moderate to severe disease severity. A novel thoracic CT disease severity scoring system was used to independently stratify dogs into mild or moderate to severe groups. Statistical comparisons between groups were made for signalment, body weight, temperature, pulse, respiratory rate, WBC count, ventilator-acquired pulmonary mechanics (specific compliance and resistance), change in arterial partial pressure of oxygen post-BAL, and outcomes. Seventeen dogs were prospectively enrolled. A comparatively lower heart rate at presentation was the only potential marker of increased disease severity identified when stratified by CT severity score. Arterial partial pressure of oxygen did not significantly decrease post-BAL regardless of disease severity or stratification method. The CT scoring system significantly correlated with the pre-BAL arterial partial pressure of oxygen-to-fractional inspired oxygen ratio. Incidence of post-procedural complications was 18%, with all complications being transient. Mortality as a direct complication of diagnostics was 0%. When considering euthanasia secondary to severity of the underlying disease and poor prognosis or death due to unrelated disease, mortality was 18%. In dogs with respiratory disease undergoing advanced diagnostic procedures, the overall incidence of post-procedural morbidity was low with no mortality directly attributed to the procedures. A novel CT disease severity scoring system was utilized and shows promise as a tool for evaluation of disease severity in this patient population when compared to arterial blood gas analysis.