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Localization of Disease

Nasal Discharge

History

Nasal discharge is almost always a sign of local disease within the nasal cavity, however there are some instances when nasal discharge can occur with lower respiratory, gastrointestinal, or systemic disease. One exception to a purely nasal localization of nasal discharge is eosinophilic bronchopneumopathy, an inflammatory condition of the epithelial lining of the airways and lungs that can also involve the nasal epithelium. Affected animals can have nasal signs that last longer or are more noticeable to owners than are lower respiratory signs. 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 that coughs airway material into the nasopharynx, which subsequently drains from the nose. This happens less commonly in the cat. Thirdly, some animals with vomiting or regurgitation will display nasal discharge because of nasopharyngeal regurgitation of gastrointestinal contents. This might be more common in brachycephalic breeds, which frequently develop pharyngeal collapse associated with increased inspiratory respiratory effort (Pollard et al. 2018). Brachycephalic animals also are prone to oral mishandling of food 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 brachycephalic animals, with brachycephalic dogs affected more often than cats. Finally, nasal discharge, particularly sanguinous nasal discharge, can be encountered in systemic diseases associated with coagulopathies (thrombocytopenia, thrombocytopathy, coagulation factor defects), hypertension, or hyperviscosity syndrome, such as encountered with leishmaniasis and chronic ehrlichiosis.

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 onset of nasal discharge is often accompanied by sneezing, is frequently paroxysmal in nature, 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, however some dogs or cats are so severely affected that they are rapidly taken to the veterinarian to determine a plan for intervention. Occasionally, dogs with nasal foreign bodies will have resolution of signs despite continued presence of organic matter within the nose. This represents a diagnostic and therapeutic dilemma, particularly in the dog that has an appropriate signalment and exposure history for a nasal foreign body. Failure to investigate signs and potentially retrieve a foreign body can have long‐term consequences due to migration of the foreign body into the central nervous system or development of a secondary fungal infection. 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 various empiric therapies requires an assessment of the top differential diagnoses likely in each case 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.

a Reported causes include canine adenovirus‐2, canine parainfluenza‐3 virus, canine respiratory coronavirus, canine herpesvirus, canine distemper virus, canine influenza viruses (H3N8, H3N2, H1N1), pneumovirus, Bordetella, Mycoplasma cynos, Mycoplasma canis, and Streptococcus equi subsp. zooepidemicus. 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 disorders must be considered, including coagulopathies, hyperviscosity syndrome, and systemic hypertension.

Nasal discharge that is strictly unilateral is most suspicious for local disease caused by a foreign body, trauma, tooth root abscess or oronasal fistula, or for an early fungal infection or neoplasm. However, arterial hypertension or a coagulopathy can also result in unilateral nasal bleeding despite being a systemic disease. Interestingly, inflammatory diseases such as lymphoplasmacytic rhinitis in the dog and feline chronic rhinosinusitis can present with lateralizing clinical signs, although in most of these cases, imaging and histology reveal that both sides of the nasal cavity are affected.

Non‐respiratory history that should be collected includes environmental exposure to foreign bodies, previous trauma, and evidence of vomiting or regurgitation. For animals with epistaxis, potential exposure to rodenticides or vector‐borne diseases that can result in thrombocytopenia, thrombocytopathy, or vasculitis (such as Ehrlichia or Rocky Mountain Spotted Fever) should be identified. In addition, history should be scrutinized for signs consistent with systemic diseases such as hyperthyroidism, renal disease, or adrenal disease, which can result in arterial hypertension.

Signalment

Young animals with nasal discharge are most often affected by infectious upper respiratory tract diseases. A nasopharyngeal polyp should be considered when discharge is accompanied by obstructed breathing, stertorous respirations, gagging, or retching. Primary ciliary dyskinesia is a defect of innate immunity inherited in an autosomal recessive fashion that causes ineffectual mucociliary clearance, trapping of secretions, and recurrent infection. Therefore, this condition is frequently recognized in a younger animal. Affected dogs are often purebred, with an increased prevalence in the Bichon Frise, Old English Sheepdog (Merveille et al. 2014), and Newfoundland (Watson et al. 1999); genetic mutations have also been reported in the Alaskan Malamute (Anderegg et al. 2019), and Rough Collie (Hug et al. 2019) although any breed of dog or cat can be affected. While neoplastic disease most typically affects...