Nasal disease is a relatively common reason for presentation of dogs and cats in practice, and is also a common reason for referral. Investigations are aided by equipment such as endoscopy, magnetic resonance imaging (MRI) or computed tomography (CT) which may not be available to the general practitioner and which are undoubtedly extremely helpful towards making a diagnosis in some cases of nasal discharge. A large amount of information, however, can be gained by following a step-by-step approach as suggested below without the need for more advanced diagnostics in the majority of patients.

Signalment

Certain diseases present more commonly in particular age groups or nose conformation (e.g., cleft palate in brachycephalic puppies) and this consideration will aid in forming a list/order of differential diagnoses.

History

A detailed history is essential as the first step towards a diagnosis and it is important to obtain a thorough background history in addition to that pertaining to the nasal discharge because, although most patients presenting with nasal discharge will have disease of the nose or sinuses, occasionally the nasal disease may be secondary to systemic disease.

The owners should be questioned so that a clear picture is obtained about how the disease first presented, and any progression. It is important to determine if the nasal discharge was preceded by sneezing, was initially unilateral or bilateral, the type of discharge (e.g., serous, mucopurulent), if the signs have altered with progression of the disease or with treatment, and if the patient shows signs of nasal pain.

Clinical Examination

A full clinical examination should be performed, then assess in detail as in Figure 1.

Figure 1. Clinical examination of animal with nasal discharge.

Pre-Anaesthetic Diagnostics

Haematology and Biochemistry

This is performed prior to proceeding with investigations under general anaesthesia and although it is unlikely to establish the cause of the nasal discharge will give information on any underlying systemic disease (unlikely) or other concurrent disease.

Blood Clotting

Some clinicians prefer to perform this in all patients that will have nasal biopsies taken; it is recommended that clotting times should be performed in patients with epistaxis, sanguinous nasal discharge, low platelet count or if the history supports the possibility of an underlying or concurrent clotting disorder.

Fungal Serology

Aspergillus serology should be performed in dogs with a history of nasal discharge; these tests do provide false-negatives and -positives and the results should be taken into consideration with all the historical and investigative findings. Cryptococcus serology is both very sensitive and specific test in cats.

Viral Testing in Cats

Feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) testing should be performed in cats because immune compromise can predispose to other disease (e.g., cryptococcal infection). If upper respiratory viral infection is suspected in cats oropharyngeal swabs should be collected and placed in viral transport medium for isolation of feline herpesvirus 1 (FHV-1) and feline calicivirus (FCV), alternatively polymerase chain reaction (PCR) may be performed for FHV-1. Swabs can be taken from the conjunctiva to isolate Chlamydophila felis and FHV-1. Oropharyngeal swabs can also be submitted if Bordetella bronchiseptica or Mycoplasma spp. infections are suspected.

Note: It is not useful to culture swabs of nasal discharge for bacterial and fungal growth because most of the diseases causing nasal discharge have secondary associated bacterial infection. Any bacteria cultured will not be the cause of the disease and a positive or negative growth of Aspergillus does not confirm or rule out this disease, respectively.

Diagnostics Under General Anaesthesia

Oral Examination

Thorough examination of the oral cavity, if not possible in the conscious patient, should be performed under GA. The teeth should be carefully examined for evidence of disease, the gingival sulcus of maxillary teeth should be probed. The palate should be examined, masses in the nasopharynx may cause deformity/ventral deviation of the soft palate and be palpable through the palate. The soft palate can be gently pulled forwards by passing a curved instrument around its caudal border. Nasopharyngeal polyps in cats, and foreign bodies such as blades of grass, can be easily accessed in this manner.

Radiography

This is the least sensitive way of imaging the nasal cavity, but the most readily available. It is generally recommended that two views of the nasal cavity are taken and a rostrocaudal view of the skull to skyline the frontal sinuses. The radiographs should be assessed for symmetry, loss of turbinate detail by either bony destruction or by obscuring or replacement with soft tissue opacity, soft tissue replacement of the normal air-filled cavities and the integrity of the boundaries of the nasal cavity.

Computed Tomography and Magnetic Resonance Imaging

These techniques give a lot more detailed information on the nature and extent of the disease process but are not widely available to all veterinary surgeons, or may not fall within a client's budget.

Endoscopy

A small flexible endoscope can be retroflexed around the soft palate (nasopharyngoscopy) which may demonstrate masses or foreign bodies at the caudal choana. Use of a dental mirror and spay hook to obtain a view of this area has been advocated by some clinicians when a suitable endoscope is unavailable.

Rhinoscopy using a small rigid or flexible endoscope is performed carefully because it is very easy to injure the nasal mucosa causing haemorrhage which will obscure the view. Nasal discharge can also obscure the view; discharge and haemorrhage can be removed by flushing with saline.

Histopathology

If a definite abnormality is seen during rhinoscopy a biopsy can be performed via passage of biopsy instruments along the biopsy channel of the endoscope, or alongside the endoscope. Following biopsy, haemorrhage is likely to obscure the view necessitating saline lavage. Alternatively, biopsies can be performed by either a blind grab technique or by an aspiration technique using a cut-down dog urinary catheter. Regardless of the biopsy technique the instruments should not be advanced beyond the level of the medial canthus to avoid damage to the cribriform plate (and beyond!). If endoscopy equipment is unavailable or nasal discharge/ haemorrhage obscures further viewing then the site of the abnormality can be assessed from the radiographs and the biopsy instrument advanced to this estimated location. Biopsies should be performed even if an abnormality is not identified on radiography or rhinoscopy. Tissue and foreign bodies may also be dislodged, using a forced nasal flush technique (see below).

Rhinotomy/Exploration of the Frontal Sinuses

Rarely, if less invasive methods have failed to give a diagnosis, surgical exploration of the nasal cavity or frontal sinuses is necessary to obtain tissue for histopathological analysis, or to search for/remove a nasal foreign body.

Saline Nasal Flush

This is useful for dislodging foreign bodies or pieces of tissue (usually tumour) from the nasal cavity. Samples can also be collected and submitted for cytological evaluation. The cuff of the endotracheal tube should be inflated snugly and/or the nasopharynx packed. The patient is positioned in sternal recumbency with their nose tipped over the edge of a table and pointing downwards. A saline-filled syringe is then placed into one nares and saline (suggest 5 ml in cat and small dog, 20 ml in medium/large dog) is flushed 'vigorously' through the nasal cavity. The procedure can be repeated multiple times on each side.

The lavage solution is collected in a bowl and will exit from the nostrils and the nasopharynx. Note: excessive force may disrupt a diseased cribriform plate!

Cytology

Samples for cytological evaluation can be obtained from the nasal cavity:

 Using a guarded brush technique

 Tissue samples collected for histopathological analysis can be touched on to a glass slide to make a smear before the sample is placed into formalin

 Via a nasal flush

Smears made from the nasal discharge can occasionally demonstrate fungal hyphae, but are unhelpful in many cases.

Culture

This has limited usefulness because normal cats' and dogs' nasal cavities contain a variety of bacteria and fungal spores. It may be useful in guiding antibiotic therapy in chronic cases of nasal disease, it must be remembered that the bacterial 'infection' in these cases is likely to be secondary. Treatment with antibiotics will improve/resolve the nasal discharge in many patients with nasal disease but will not treat the underlying cause and recurrent discharge is likely on discontinuation of the antibiotics.