Bronchoscopy and Airway Sampling in Dogs and Cats with Chronic Cough

In dogs and cats with chronic cough, thoracic radiographs may not fully explain the airway abnormality responsible for persistent clinical signs. Bronchoscopy provides a closer look at the trachea and bronchi and, importantly, allows airway samples to be collected during the same procedure. 

What Can Bronchoscopy Detect? 

Bronchoscopy can identify tracheal and bronchial collapse, bronchomalacia, distal airway collapse, foreign bodies, mucosal lesions, airway narrowing, and bronchiectasis^[1]. 

It is particularly valuable when direct assessment of the airway is needed. Tracheal collapse, for example, can be graded according to the degree of reduction in the airway lumen: grade 1 represents approximately 25% reduction, grade 2 approximately 50%, grade 3 approximately 75%, and grade 4 more than 90% reduction^[1]. 

The appearance of the airway mucosa can also provide useful information. In dogs with chronic bronchitis, the mucosa may be roughened, non-glistening, thickened, granular, erythematous, and associated with increased mucus^[1],[2]. 

The Larynx Deserves Attention Too 

Chronic cough is not always explained by a thoracic abnormality. 

A complete sedated oral examination can be useful when thoracic radiographs do not identify the cause of coughing. Laryngeal paralysis or paresis was identified in 19% of dogs in which cough was the primary problem, without other upper airway abnormalities^[1]. 

Endoscopy can also evaluate the caudal nasal cavities, choanae, rostral nasopharynx, oropharynx, larynx, and large airways. When a dog or cat has coughing along with sneezing or nasal discharge, rhinoscopy can help investigate the upper respiratory tract^[3]. 

Visual Findings are Only Half the Picture 

One of the major advantages of bronchoscopy is the ability to obtain samples directly from the respiratory tract. 

Endoscopic techniques can provide material for cytology, histology, and culture. Bronchial brushings can be used for cytological evaluation, while bronchoalveolar lavage can provide samples for cytology and microbiological testing, including aerobic and anaerobic culture, Mycoplasma culture, and/or PCR^[1],[4]. 

These samples can contribute to the investigation of inflammatory disease, neoplasia, and infectious causes. 

Airway Collapse May Accompany Chronic Bronchitis 

Bronchoscopy can reveal additional airway abnormalities that influence the clinical picture. 

Approximately one-third of dogs with chronic bronchitis have intrathoracic airway collapse during expiration. Dogs with this finding have a worse prognosis than those with chronic bronchitis without intrathoracic airway collapse. 

Dorsal tracheal membrane collapse is also commonly observed with chronic bronchitis and should be distinguished from the collapse of the tracheal cartilage. 

In cats with chronic bronchitis, airway collapse is less common because their airways are narrower, although it can still occur. 

Combining Examination with Sampling 

Bronchoscopy can provide information that cannot be obtained from airway imaging alone. It allows the veterinarian to assess airway structure and dynamics, identify mucosal abnormalities or foreign material, and collect samples for laboratory evaluation. 

For dogs and cats with persistent chronic cough, direct airway examination combined with targeted sampling can help move the investigation from identifying that an airway problem exists to characterizing what is actually causing it.

References:

1. Hsieh BM, Beets AK. Coughing in small animal patients. Frontiers in Veterinary Science. 2020 Jan 21;6:513. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2019.00513/pdf
2. Oyama MA, Rush JE, Rozanski EA, Fox PR, Reynolds CA, Gordon SG, Bulmer BJ, Lefbom BK, Brown BA, Lehmkuhl LB, Prosek R. Assessment of serum N-terminal pro-B-type natriuretic peptide concentration for differentiation of congestive heart failure from primary respiratory tract disease as the cause of respiratory signs in dogs. Journal of the American Veterinary Medical Association. 2009 Dec 1;235(11):1319-25. https://www.holisticandorganixpetshoppe.com/uploads/7/8/8/4/7884424/javma200912-assessment-ntprobnp.pdf
3. Hunt GB, Perkins MC, Foster SF, Barrs VR, Swinney GR, Malik R. Nasopharyngeal disorders of dogs and cats: a review and retrospective study. Compendium. 2002 Mar;24(3):184-203. https://www.researchgate.net/profile/Richard-Malik/publication/282493677
4. Zhu BY, Johnson LR, Vernau W. Tracheobronchial brush cytology and bronchoalveolar lavage in dogs and cats with chronic cough: 45 cases (2012–2014). Journal of Veterinary Internal Medicine. 2015 Mar;29(2):526-32. https://academic.oup.com/jvim/article-pdf/29/2/526/66689405/jvim12566.pdf