Chronic Rhinitis in Dogs

Chronic nasal disease is commonly encountered in dogs in the practice, but diagnosis and treatment can be frustrating and often unrewarding. This discussion will focus on chronic nasal disease, as it is generally more challenging to manage than acute disease.

The nasal cavity extends from the external nares to the choanae with a dividing septum. It contains the nasal conchae – cartilaginous scrolls covered with mucosa. Numerous delicate bony scrolls are known as ethmoturbinates and make up the ethmoidal conchae. The air space is divided into three longitudinal nasal meatuses: dorsal, middle and ventral. The function of the nasal cavity is to warm and moisten air and filter out foreign bodies, and it also has a role in thermoregulation. The nasopharynx extends from the choanae to the intrapharyngeal ostium. The most important paranasal sinus in the dog is the frontal sinus.

History, examination and differential diagnoses

Historical and clinical signs of nasal disease include nasal discharge, sneezing and discoloration of the external nares. History taking should include questions on chronicity and progression of the disease, any changes to color of the external nares and visible nasal mucosa, character of any discharge, and whether discharge is unilateral or bilateral. Physical examination of the oral cavity is useful – particularly in paying attention to the presence of dental disease. Examining the nose is often limited to observing any discharge and changes to the external nares. Airflow through each nostril can be assessed with a wisp of cotton wool.

Differential diagnoses can be narrowed by historical and physical findings. Acute onset sneezing, particularly after a walk, increases the suspicion of a foreign body. A chronic unilateral nasal discharge, with or without blood, increases the suspicion of a nasal tumor or foreign body. Loss of pigmentation of the external nares raises the suspicion of aspergillosis. The main differential diagnoses for chronic nasal disease includes foreign body, chronic rhinitis, dental disease, neoplasia and aspergillosis. A study of 42 dogs with persistent nasal discharge (Tasker et al, 1999), 33 per cent were diagnosed with neoplasia, 24 per cent with inflammatory rhinitis, 10 per cent with periodontal disease, seven per cent with foreign bodies and seven per cent with aspergillosis. A more recent Canadian study (Meler et al, 2008) produced similar findings, with 24 per cent non-specific rhinitis, 15 per cent neoplasia, nine per cent aspergillosis, nine per cent cleft palate and four per cent periodontal disease. A South African study (Lobetti, 2009) found 47 per cent of cases were neoplastic, with lymphoplasmacytic rhinitis in 20 per cent and fungal rhinitis in 11 per cent. Uncommon causes of chronic nasal disease in dogs include nasal polyps (Holt and Goldschmidt, 2011) and nasal mites (Pneumonyssoides caninum).

Diagnostic tests

Advanced imaging

Magnetic resonance imaging (MRI) and computed tomography (CT) can provide valuable information about the structure of the nasal cavityand provide excellent images of the soft tissue and small bones, and can be used to help distinguish between: aspergillosis, which tends to show a destructive pattern; neoplasia, which tends to show a soft tissue mass often accompanied by bony destruction; and chronic rhinitis, which will usually show only an increase in retained secretions. Occasionally, foreign bodies will be detected on advanced imaging, but rhinoscopy is superior for this. Advanced imaging allows assessment of the frontal sinuses, which is more sensitive than radiography. In terms of sensitivity for nasal imaging, there is little difference between MRI and CT.

Radiography is often useful in diagnosing chronic nasal disease, although in recent years it has become increasingly supplanted by advanced imaging techniques. In many cases, there are radiological findings that can be considered diagnostic – therefore, radiography is recommended as part of the initial investigation. The most useful radiographic projection is the dorsoventral intraoral. If possible, use of non-screen film is ideal, since the resolution is superb and it can be placed caudally into the mouth to capture most of the nasal cavity. Film in a cassette (and digital or computed radiography) can nonetheless be used to make useful images. A second projection, which is particularly useful, is the rostrocaudal (skyline) view of the frontal sinuses. The lateral projection rarely adds to the diagnosis.

Rhinoscopy is a particularly useful diagnostic procedure. A complete examination includes both anterior rhinoscopy via the nostrils and retrograde examination of the nasopharynx. Both require general anaesthesia for patient comfort and safety (and protection of the equipment). Selecting the right equipment is critical for success. Anterior rhinoscopy is most useful when a rigid endoscope is used: in large dogs a 4mm scope can be used, but in other cases a 2.7mm scope is required. Although rhinoscopy can be performed “dry”, with no irrigation and without a sheath, most clinicians prefer to use an operating sheath with the scope, which allows constant irrigation and passage of biopsy forceps through an instrument channel. Instrumentation marketed for cystoscopy is ideal. Use of a camera system is recommended. Rhinoscopy should be completed in a systematic manner to examine each meatus. In larger dogs, or when turbinate destruction is present, it may be possible to enter the nasopharynx and/or frontal sinus.

Nasal flushing Cytological findings from nasal flushes are generally considered to be less sensitive and specific than histopathological findings from biopsies. Occasionally, forceful flushing will expel pieces of tissue that can be submitted for histology. Since chronic nasal disease is rarely a specific bacterial infection, microbiology is of limited value. Fungal culture is potentially misleading, since Aspergillus is a common environmental organism and is sometimes cultured from nasal flushes taken in other diseases.

Nasal biopsies are most useful for diagnosing nasal neoplasia, although when typical radiographic changes are present, a tissue diagnosis is only of academic interest unless the owners are considering advanced therapy, such as radiotherapy. When rhinoscopy clearly demonstrates proliferative tissue, biopsy forceps can be placed, under visual guidance, to the area of interest. As a general rule, the larger the forceps, the more reliable the pathological diagnosis: if a small cystoscope is used, the instrument channel will not accommodate forceps of a sufficient size and larger forceps are placed alongside the scope. In animals with widespread radiographic changes suggestive of neoplasia, an excellent alternative is suction biopsy

Treatment

Neoplasia

Nasal neoplasia surgery is considered ineffective, with survival times comparable to those observed in untreated dogs. Chemotherapy can be used in nasal lymphoma, although, if this is solitary, radiotherapy may be more effective. However, the literature on this subject is sparse. Most nasal neoplasia is best treated with radiotherapy. Median survival times vary in the literature, depending on protocol, study population and whether re-irradiation is performed on recurrence, ranging from 146 days (Gieger et al, 2008) to 927 days (Bommarito, 2011).

Chronic rhinitis

Chronic rhinitis is a frustrating condition to treat. Control may be achieved with long-term corticosteroids, but sometimes no response is achieved. Steam inhalation can sometimes help to moisten and clear dessicated nasal secretions.

Aspergillosis

Historically, various treatment regimes have been used for aspergillosis with varied success. No agents are licensed for this purpose in the UK. Notably, systemic therapies appear to have a limited efficacy, probably because the organism is present on the surface of the tissues and may be poorly accessible to antifungal drugs carried in the plasma. Of the commonly available agents, itraconazole is perhaps the most useful as it is relatively nontoxic and moderately efficacious (the expected response rate is around 60 per cent). More effective are topical therapies and, for some years, the standard treatment has been clotrimazole. It is most useful delivered in an “invasive” fashion (through instillation into the frontal sinuses, rather than via the nostrils). Several regimes are described, but the most reliable is through surgical access to the sinuses (for example, by trephination). Large volumes of saline are used to flush the sinuses and nasal chambers, followed by 1.0ml/kg of clotrimazole solution, and then the frontal sinuses are filled with clotrimazole ointment. Most dogs are successfully treated by a single infusion, but it is repeated at three-week intervals – twice in animals with persistent signs (Sissener et al, 2006). Alternatives to clotrimazole are reported, but should be reserved for the rare cases that fail to respond and after discussion with clinicians experienced with such cases.

Conclusion

Chronic nasal disease in dogs can be challenging to treat and diagnose. However, with a rigorous approach, a diagnosis can often be made, allowing the most appropriate treatment to be selected.