Rhinitis in Dogs

Ned F. Kuehn, Southfield, Michigan

Sneezing and nasal discharge usually are associated with diseases of the nose, paranasal sinuses, and nasopharynx. Sneezing frequently precedes the onset of notable nasal discharge. The severity and frequency of sneezing may diminish over time, whereas the nasal discharge frequently worsens in severity and changes in character. Therefore dogs with chronic rhinitis frequently have chronic nasal discharge rather than persistent sneezing. The nature of sneezing may aid in localizing the region of the problem. Expiratory sneezing typically is associated with sinus or intranasal disease. Reverse or inspiratory sneezing (aspiration reflex) is a normal response to mechanical irritation of the dorsal nasopharyngeal mucosa. The presence of reverse sneezing is usually correlated with caudal nasal, nasopharyngeal, or sinus disease. Some dogs may have posterior rather than anterior nasal discharge, and the only indication of primary nasal disease may be obstructive nasal breathing.

The causes of nasal discharge and obstructive nasal breathing in the dog are listed in Box 154-1. The principal diseases associated with chronic rhinitis are sinonasal neoplasia, idiopathic lymphoplasmacytic rhinitis, and fungal rhinitis (Lefebvre et al, 2005). Nasal discharge is not limited to primary nasal disease but also may occur with systemic and extranasal disorders. Extranasal disorders often have systemic signs (e.g., depression, pyrexia, hemorrhage) and a history of acute onset, whereas primary nasal disorders have a more chronic nature. Important extranasal disorders that may manifest with nasal discharge include coagulopathies, vasculitis, hypertension, hyperviscosity syndrome, and pneumonia.

Box 154-1 Differential Diagnosis for Nasal Discharge or Obstructive Nasal Breathing

Nasal and Paranasal Sinus Disorders

• Allergic rhinitis

• Bacterial rhinitis (Bordetella bronchiseptica, Pasteurella multocida)

• Ciliary dyskinesia

• Dental disease

• Foreign body

• Fungal rhinitis (Aspergillus fumigatus, Penicillium spp., Rhinosporidium seeberi, Cryptococcus neoformans)

• Hyperplastic rhinitis (Irish wolfhounds)

• Idiopathic lymphoplasmacytic rhinitis

• Nasal polyps

• Nasopharyngeal stenosis

• Nasopharyngeal turbinates

• Neoplasia

• Nasal parasites (Pneumonyssus caninum, Eucoleus [Capillaria] boehmi, Cuterebra spp.)

• Oronasal fistula

• Palatine defects

• Trauma

• Viral rhinitis (canine distemper)

Viral Infection and Extranasal Disorders

• Coagulopathies

• Cricopharyngeal disease

• Environmental agents (dusts, smoke)

• Esophageal stricture

• Hypertension

• Hyperviscosity syndrome

• Immunoglobulin A immunodeficiency

• Megaesophagus

• Oropharyngeal diseases

The character and type of nasal discharge may be helpful in developing a list of potential causes, but these findings are not characteristic for specific diseases. Unilateral discharge is often associated with neoplasia, fungal and foreign body rhinitis, and dental disease. Bilateral discharge is typical of systemic disorders, advanced neoplasia or fungal rhinitis, idiopathic lymphoplasmacytic rhinitis, and allergic rhinitis. However, it also is possible for systemic disorders and idiopathic lymphoplasmacytic rhinitis to present with only unilateral nasal discharge. Serous nasal discharge may be seen initially in a variety of nasal diseases but often becomes mucopurulent as disease progresses and secondary bacterial invasion occurs. Mucopurulent nasal discharge is most common and indicates bacterial infection secondary to an underlying disorder that has damaged the nasal mucosa with resultant bacterial invasion. Primary bacterial infection is an exceedingly rare cause of rhinitis in dogs. Mucopurulent and serous discharges may be blood tinged as a result of mucosal erosion. Epistaxis usually results from an underlying nasal disorder causing erosion of a major blood vessel but also may be seen with systemic disorders such as coagulopathies, hypertension, vasculitis, or hyperviscosity syndrome.

Diagnosis

Clinical history and physical examination findings generally offer an indication of primary nasal disease as opposed to systemic or extranasal disease. Routine laboratory tests (complete blood count, serum chemistry panels, urinalysis), coagulation profile, blood pressure, and thoracic radiographs are important to rule out most of the systemic or extranasal causes of nasal discharge. Cytologic evaluation of nasal discharge is rarely helpful except possibly for identification of Eucoleus (Capillaria) boehmi parasitic ova. Performing bacterial and fungal cultures of nasal discharge is not recommended because results are nonspecific and simply represent resident bacteria and fungi. Serologic testing for aspergillosis should be considered, because a positive result is highly suggestive of disease, although a negative result does not rule out nasal infection (Pomrantz et al, 2007). Empiric antimicrobial treatment is not advised and merely delays definitive diagnosis unless chronic Bordetella bronchiseptica or Pasteurella multocida rhinitis (both very rare) or pneumonia is present.

Diagnostic imaging studies are performed with the patient under anesthesia. Imaging studies often are essential in dogs with chronic rhinitis to help reach a diagnosis. It is critical that imaging studies be completed before rhinoscopy or collection of intranasal samples so that blood from secondary hemorrhage does not obscure subtle lesions or affect the quality of diagnostic images. If dental disease is suspected, dental radiographs are recommended to evaluate teeth and surrounding structures. Radiographic images of the nose and sinuses may provide some insight but often do not reveal a specific cause of the nasal disease. Radiographs often lack sufficient resolution to identify or localize early nasal disease. Computed tomography (CT) is vastly superior to plain radiography of the nasal cavity (Lefebvre et al, 2005). Nasal CT provides a thorough assessment of the nasal cavities and paranasal sinuses and provides superior insight into the nature and extent of disease. Contrast-enhanced CT images are useful to distinguish between vascularized soft tissue and mucus accumulation. Because nasal CT clearly demonstrates the location and extent of nasal disease, it is often used to help guide postimaging rhinoscopic and biopsy procedures and delineate nasal tumors for radiation therapy. If routine diagnostic steps do not provide a cause for rhinitis, referral to an institution providing CT imaging is advised. Although magnetic resonance imaging (MRI) is often considered superior to CT for delineation of tumor borders, a recent study failed to document an advantage of MRI over CT in detecting intracalvarial changes in dogs with nasal neoplasia (Dhaliwal et al, 2004).

Rhinoscopy should be performed only after all imaging studies are completed and with the patient still under anesthesia. The nasopharynx is examined before the nasal cavity, because if hemorrhage is induced by examination of the nasal cavities, blood frequently pools in the nasopharynx and obscures visualization of this area. Retroflex nasopharyngoscopy is performed by turning a small flexible scope 180 degrees around the caudal margin of the soft palate to evaluate the caudal nares, dorsal soft palate, and nasopharynx. Tumors or foreign bodies lodged within the caudal nares or within the nasopharynx occasionally cause rhinitis in dogs. Anterior rhinoscopy may be limited by the size of the nasal cavity compared with the size of the scope, lesion location, and difficulty in visualizing intranasal structures because of mucus or hemorrhage. The convoluted nature of the nasal passages does not allow for evaluation of the entire nasal cavity; thus foreign bodies and neoplastic masses may be overlooked. The mucosa should be evaluated for color, vascularity, friability, edema, and presence of parasites or fungal plaques. The nasal passages should be evaluated for obstruction by tissue masses, foreign bodies, and secretions. A loss of normal nasal turbinates indicates the presence of a destructive rhinitis secondary to fungal infection or severe idiopathic lymphoplasmacytic rhinitis. Rhinoscopy is especially helpful in the diagnosis of fungal rhinitis and rostrally positioned nasal foreign bodies. Fungal rhinitis often is associated with widespread turbinate destruction, and rhinoscopy may reveal a cavernous nasal cavity with off-white to gray fungal plaques scattered across the surface of the nasal mucosa.

Procurement of nasal specimens and biopsy of nasal tissue should be performed only after imaging and visual examinations are completed and while the patient is still under anesthesia. Tissue from lesions visualized during rhinoscopy may be obtained by direct biopsy with forceps passed either adjacent to or through the endoscope. Analysis of specimens obtained by rhinoscopically directed biopsy of masses identified within the nose can be limited by the size of the tissue samples recovered and inflammation surrounding the mass. Lymphoplasmacytic inflammation often is present with intranasal neoplasms, whereas idiopathic lymphoplasmacytic rhinitis is not associated with mass lesions in the nose. I prefer to use nasal CT images to guide instrumentation for procurement of biopsy samples. Depending on the size of the nose, either small (2- to 4-mm) clamshell or colonic biopsy forceps are advanced to the site of disease as identified from CT images, and multiple biopsy specimens are then obtained. During the biopsy procedure it is recommended that the dog be in sternal recumbency with the rostral end of the nose directed downward to facilitate drainage of escaping blood away from the nasopharynx and oropharynx. Following biopsy, the tip of the nose remains positioned downward, and the oropharynx and cranial esophagus are suctioned to remove blood clots. Nasal lavage may be required to dislodge foreign material identified or suspected to be present within the nose. The rostral aspect of the nose should be directed downward while copious amounts of saline are flushed vigorously through the nostrils. The endotracheal tube cuff should be inflated to prevent aspiration pneumonia. Some clinicians surround the glottis with surgical sponges or gauze.

Tissue samples are not submitted routinely for bacterial or fungal culture except when fungal plaques are detected (Pomrantz et al, 2007) or sometimes when a foreign body is identified. To confirm a diagnosis of aspergillosis, a positive result on fungal culture should be supported by diagnostic imaging, cytologic, rhinoscopic, or histologic evidence of infection. Primary bacterial rhinitis is exceedingly rare in the dog, and almost all bacterial infections develop secondary to underlying primary nasal disease. A heavy growth of even one or two bacterial isolates may merely be indicative of bacterial colonization; however, pure isolates of B. bronchiseptica and possibly of P. multocida may be significant if the clinical history is supportive. If tissue cultures are performed, the results must be interpreted carefully in light of histopathologic and other diagnostic information.

A thorough oral examination with inspection of the hard palate, oropharynx, and dental structures should be performed. A periodontal probe should be used to inspect the gingival sulci of maxillary teeth. Oronasal fistulae are often associated with the maxillary third incisors, first and second premolars, and mesial root of the third premolar.

Treatment of Common Causes of Rhinitis

Geographic locality plays a role but, excluding nasal foreign bodies (Aronson, 2004) and dental disease, the most common causes of chronic rhinitis in dogs are neoplasia, idiopathic chronic (lymphoplasmacytic) rhinitis, and fungal rhinitis. Parasitic rhinitis is uncommon. The treatment for nasal mites (Pneumonyssus caninum) is ivermectin 0.2 mg/kg PO, with the dose repeated in 2 to 3 weeks. Selamectin has been reported effective at 6 to 24 mg/kg for three doses at 2-week intervals, and milbemycin is recommended for use in dogs with possible MDR-1 (multidrug resistance protein 1) mutations using a dosage of 0.5 to 1.0 mg/kg body weight PO once a week for 3 weeks. The treatment for nasal nematodes (E. [Capillaria] boehmi) is not clearly defined, although ivermectin 0.2 mg/kg PO once or fenbendazole for 2 weeks reportedly have been effective. Allergic rhinitis often is mild, but if it is severe, antihistamines such as diphenhydramine, chlorpheniramine, or trimeprazine/prednisone (Temaril-P) may be prescribed to control clinical signs. In the rare situation of bacterial rhinitis caused by B. bronchiseptica, doxycycline 5 to 10 mg/kg every 12 hours PO for 2 weeks may be effective.

Fungal Rhinosinusitis

Fungal rhinitis is a relatively common cause of chronic rhinitis in the dog in various geographic regions throughout the world. Aspergillus fumigatus is the most common cause of fungal rhinitis in dogs, but occasionally Penicillium spp., Rhinosporidium seeberi, and very rarely Cryptococcus neoformans may cause disease in dogs. R. seeberi is associated with the growth of a granulomatous mass within the rostral nasal cavity. Cytologic examination of tissue from these granulomatous masses often is diagnostic. Treatment for rhinosporidiosis is best accomplished by aggressive surgical resection of the granulomatous mass.

Nasal aspergillosis is most commonly seen in young to middle-aged dolichocephalic dogs, although older-aged dogs should not be excluded. Sinonasal aspergillosis is a noninvasive disease in dogs with fungal hyphae confined to the surface of the mucosa and not within or below the surface mucosa. The bony destruction seen with this disease is not caused by the fungus itself but appears to result from the host inflammatory response due to an aberrant dysregulation of innate and adaptive immune responses. Systemic immunosuppression is not present in affected dogs. Local immune-dysfunction owing to imbalance between proinflammatory and antiinflammatory signals is likely involved in the pathogenesis of this disease. Dysregulation of genes encoding Toll- and Nod-like pattern recognition receptors involved in the innate immune response in the nasal mucosa of dogs with sinonasal fungal rhinitis has recently been described (Mercier et al, 2012).

Affected dogs often have copious unilateral or bilateral mucopurulent nasal discharge. The volume of nasal discharge is often less in dogs with primary fungal frontal sinusitis. Sneezing is common and may be accompanied by mild to severe epistaxis. Facial pain and depigmentation and ulceration of the nasal planum may be present. Unlike in nasal neoplasia, facial distortion is unusual in all but advanced cases of fungal rhinitis. Nasal CT images (Figure 154-1) along with rhinoscopy findings are noteworthy for the presence of dramatic turbinate loss within the nasal cavity (Saunders et al, 2004). Frontal sinus involvement may be present and is characterized on CT by an irregularly marginated soft tissue attenuating density within the affected sinus (see Figure 154-1). Mucosal thickening and bone remodeling of the affected sinus may also be seen. Invasion through the maxillary or palatine bones with extension into surrounding soft tissue structures is seen occasionally. Nasal CT is preferred over radiography so that the integrity of the cribriform plate can be evaluated before local antifungal therapy is initiated. Diagnosis of nasal aspergillosis is confirmed by visualization of fungal plaques on nasal or sinus mucosa and demonstration of branching septate hyphae on cytologic or histologic examination of samples from affected regions within the nose. Serologic tests positive for aspergillosis also support the diagnosis, although negative results may occur even with extensive disease. Occasionally special staining methods for fungi may be useful for identifying fungal elements in tissue biopsy samples. Repeated sampling or a trial of antifungal drugs may well be indicated in dogs for which the index of suspicion for nasal aspergillosis is high; however, extensive débridement of fungal plaques should be performed before treatment.