hope that this second edition of my textbook will instill confidence in students and practitioners as they identify and manage respiratory conditions of dogs and cats.
Acknowledgments
I remain grateful to the clients and patients who have both tested and expanded my knowledge.
This work was completed with the support of my colleagues at UC Davis, who have afforded me the opportunity and freedom to pursue respiratory medicine as my passion. Clinicians and house officers in all services have supported my clinical efforts as well as my research, and my departmental colleagues and the School’s leadership have been both encouraging and accommodating
This book is the result of years of discovery and clinical effort, and it would not have been possible without the inspiration from colleagues and collaborators in the USA and worldwide who share a fascination with and great knowledge of respiratory medicine. The veterinarians I have met through the American and European Colleges of Veterinary Internal Medicine and the Veterinary Comparative Respiratory Society have motivated me to continue my search for knowledge.
1 Localization of Disease
Clinical signs that provide clues to the existence of respiratory disease include nasal discharge, cough, respiratory noise, tachypnea, difficulty breathing, or exercise intolerance. The first step in making a diagnosis is the accurate localization of the anatomic origin of disease within the respiratory tract: the nasal cavity, upper or lower airway, lung parenchyma, or pleural space. Achieving appropriate anatomic localization of the site of dysfunction will allow construction of an accurate list of differential diagnoses, will facilitate efficient diagnostic testing, and will allow rational empiric therapy while waiting for test results.
Nasal Discharge
History
Nasal discharge is almost always a sign of local disease within the nasal cavity. One exception is eosinophilic bronchopneumopathy, an inflammatory condition of the epithelium lining the airways and the lung that can also involve the nasal epithelium. Interestingly, cats with eosinophilic lower airway disease do not display this clinical finding. Nasal discharge can also accompany infectious lower respiratory tract disease in the dog (or occasionally the cat) that coughs airway material into the nasopharynx, which subsequently drains from the nose. Finally, some animals with vomiting or regurgitation will display nasal discharge because of nasopharyngeal regurgitation. This might be more common in brachycephalic breeds, which frequently develop pharyngeal collapse due to increased respiratory effort (Pollard et al. 2018). Brachycephalic animals also are prone to mishandling of food orally due to excessive pharyngeal folds and because of multiple gastrointestinal diseases, including hiatal hernia, gastroesophageal reflux, and mild inflammatory intestinal disease that leads to vomiting or regurgitation. All of these features contribute to nasal discharge in these animals.
The most common respiratory causes of nasal discharge include infectious, inflammatory, and neoplastic disorders as well as dental‐related nasal disease and foreign bodies (Table 1.1). Additional clinical signs that can be seen in animals with nasal disease include sneezing or reverse sneezing, pawing or rubbing at the face, noisy breathing or mouth breathing, facial pain, or an unexplained odor near the head.
When evaluating the animal with nasal discharge, important considerations include the duration of signs, the type of discharge as well as changes in its character over time, and the presence of unilateral, bilateral, or progressive signs. Acute nasal discharge is often accompanied by sneezing and is most commonly associated with infectious upper respiratory tract disease or a foreign body. Affected animals can have signs that resolve within a week without treatment or they can be so severely affected that animals are rapidly evaluated by a veterinarian to determine a plan for intervention. Occasionally, dogs with nasal foreign bodies will have resolution of signs despite the continued presence of organic matter within the nose. This represents a diagnostic and therapeutic dilemma in the dog that has an appropriate signalment and exposure history for a nasal foreign body, because failure to investigate signs and potentially retrieve a foreign body can have long‐term consequences. The most frustrating cases are those with chronic, slowly progressive nasal discharge and sneezing over weeks to months to years before the severity of disease prompts veterinary care. Prioritizing empiric therapy requires an assessment of the top differential diagnoses and determining what treatment is least likely to worsen signs, to interfere with further diagnostic testing, or to hamper the owner from pursuing specific work‐up.
Table 1.1 Causes of nasal discharge in dogs and cats.
| Dog | Cat | |
| Infectious | Canine infectious respiratory disease complexa Aspergillus Cryptocococcus Penicillium Rhinosporidium | Acute upper respiratory tract disease complexb Cryptococcus Aspergillus |
| Inflammatory | Lymphoplasmacytic rhinitis | Feline chronic rhinosinusitis |
| Neoplastic | Adenocarcinoma Sarcoma Lymphoma | Lymphoma Adenocarcinoma Sarcoma |
| Local | Tooth root abscess Oronasal fistula Trauma Foreign body Nasal or nasopharyngeal polyp | Nasal or nasopharyngeal polyp Tooth root abscess Oronasal fistula Foreign body Trauma |
| Other | Primary ciliary dyskinesia Nasal mites Xeromycteria (dry nose syndrome) | Primary ciliary dyskinesia |
a Reported causes include canine adenovirus‐2, canine parainfluenza‐3 virus, canine respiratory coronavirus, canine herpesvirus, canine distemper virus, Bordetella, Mycoplasma, and Streptococcus equi subsp. zooepidemicus. Canine influenza viruses and pneumovirus are new additions to the list of etiologic agents and novel viral organisms are continually being identified.
b Reported causes include feline herpesvirus‐1, feline calicivirus, Chlamydia, Bordetella, and Mycoplasma.
With many causes of nasal signs including viral disease or foreign body, discharge is serous initially and then progresses to a mucoid character when inflammation induces mucus production or when secondary bacterial infection develops. Yellow‐green nasal discharge can be an indicator of eosinophilic disease, but is also encountered in other infectious or inflammatory conditions, while brown‐tinged discharge suggests the presence of blood within the mucus. Bright red blood can be found in combination with nasal discharge because of trauma to blood vessels associated with the primary disease process or due to the severity of sneezing. Epistaxis with or without nasal discharge has been associated with local causes of disease, including inflammatory rhinitis, canine aspergillosis, and neoplasia; however, in animals with pure epistaxis, systemic vascular disorders must be considered, including coagulopathies and systemic hypertension.
Nasal discharge that is strictly unilateral is most suspicious for local disease due to a foreign body, trauma, tooth root abscess or oronasal fistula, or an early fungal infection or neoplasm. However, systemic vascular disease
