Clinical Approach to Chronic Upper Respiratory Tract Disease in Cats—How Rhinoscopy Can Help
E. Robertson, DABVP (Feline)
Indications, History and Physical Examination
Before conducting any endoscopic examination, it’s essential to first acquire a detailed clinical history and thorough patient examination to accurately localize the disease process. Additional general screening tests (e.g., haematology, biochemistry, electrolytes and urinalysis) can also be performed to establish the general health and potential anaesthetic risk of the patient. The depth of evaluation will vary depending on the case; however, every case should receive a comprehensive history and full clinical examination.
The indications for rhinoscopy include: chronic and/or recurring sneezing and reverse sneezing, nasal discharge, epistaxis, abnormal respiratory sounds such as stertor (nasopharyngeal) and/or stridor (laryngeal). Physical examination should therefore include an assessment of nasal air ow (decreased or normal, unilateral or bilateral change) and palpation of the palate and facial bones for pain, swelling, ipsilateral epiphora, ipsilateral exophthalmos or evidence of bony lysis.1,2 A full oral examination should ideally include a dental assessment and oropharyngeal examination. If dental disease is suspected, dental radiography may be indicated, paying special attention to teeth 104, 204, 108 and 208. Neurological examination should focus on cranial nerve evaluation and also detecting signs of cerebral dysfunction such as weakness, decreased conscious proprioception, and visual deficits indicative of invasive disease. If clinically suspicious of cryptococcosis, cytology slides of nasal secretions and latex cryptococcal antigen testing (LCAT) should be submitted, especially in those patients travelling from endemic areas (e.g., Canada, Australia, USA). A thorough otoscopic examination should be performed of the external ear canals.
Cats with epistaxis should have a coagulation profile (e.g., platelet count, PT/PTT and/or a mucosal bleeding time [MBT]) performed and their blood pressure checked prior to starting, as these patients may have an increased risk of bleeding.
Bacterial culture and antimicrobial susceptibility testing of superficial nasal swabs are often unrewarding and not generally recommended.3 Results typically yield normal intranasal bacterial flora and are difficult to interpret. Others suggest that results of culture and sensitivity testing may be useful in guiding antibacterial therapy.3 Cultures of nasal biopsy samples may be more representative for deep mucosal infections, but this has not been definitively proven.
FHV-1 or FCV virus isolation and nucleic acid amplification techniques are often used to implicate infection by these organisms. FHV-1 PCR assays are widely available, and feline calicivirus reverse transcriptase PCR assays are also available. However, none of the PCR assays for FHV-1 have been shown to distinguish between wild-type virus and vaccine virus. Additionally, test sensitivity (detection limits and rates) varies greatly between the tests and laboratories. These infectious agents can be detected in healthy cats as well as in clinically ill cats. Thus, the positive predictive value for these assays is low and thus diagnostic; cost value is questionable in those cats with chronic nasal disease.
For a complete evaluation of the nasal cavity, sinuses and nasopharynx, the assessment should include imaging such as radiographs, CT/MRI, dental radiography, and rhinoscopy.
Introduction to Rigid Endoscopy
The novice endoscopist should strongly consider participating in hands-on wet lab courses, provided by experienced endoscopists, before attempting rigid rhinoscopy in the cat. This will ensure a level of competence that justifies the potentially high learning curve and initial investment in providing this type of service.
What is a Rigid Endoscope?
In simple terms, a rigid endoscope is a long, slender stainless steel tube with a series of solid glass rod lenses which allow for the transmission of light and image.1,2 Light transmission is achieved from the use of an extracorporeal light source attached to the optical end of the endoscope. The image is then viewed via an oculus, or eye-piece, directly to the operator’s eye or a video camera which can be transmitted to a video monitor and stored in an archiving system.
Upper airway examination begins with laryngoscopy on induction. Laryngeal structure (i.e., anatomy) and function should be assessed in relation to phase of respiration. This examination should be assessed under a light plane of anaesthesia. It is vital for an assistant to ‘announce’ the phase of respiration and to not confuse normal movement with paradoxical movement found in complete laryngeal paralysis.
Caudal (Flexible) Nasopharyngoscopy
At the beginning of the procedure, a retroflexed examination behind the soft palate should be performed in attempt to exclude mass lesions, nasopharyngeal stenosis or foreign bodies. A dental mirror and bright light can sometimes provide an image of this region, or a specialised instrument with light source and a flexible mirror can be obtained from commercial vendors. A 4.0–5.0-mm diameter, two-way deflection endoscope with biopsy channel can access the nasopharynx in all but the smallest dogs or cats.
Nasal Flushing, Culture and Cytology
Vigorous nasal flushing can be useful to dislodge mass lesions or foreign bodies. Cytology of nasal flush fluid is likely to be very superficial and of limited value in most cases. In particular, neoplastic conditions may be misdiagnosed as rhinitis following the finding of inflammatory cells only on cytology.4,5 Cytology can, however, be highly diagnostic for diseases such as nasal cryptococcosis and friable tumours (e.g., lymphoma).
Rostral (Rigid) Rhinoscopy
This procedure can be performed quite easily on most feline patients using a 1.9 mm x 30 degree telescope with sheath. This instrument has two-way stopcocks for continuous fluid ingress and egress which removes blood, mucus or other tissue debris from the field of view. Another advantage of continuous fluid irrigation is that it can act as a superior medium and enhance tissue magnification compared to that of air.1 The entirety of both the dorsal and ventral nasal meatus can be examined adequately to the level of the ethmoid turbinates.
Sternal recumbency places the patient in a more ‘natural’ position in relation to the viewing monitor. The head is propped up with either a sandbag, wedge foam protected with an incontinence pad, or rolled towel. A cut-down needle cap6,7 is used as a speculum to allow for evacuation of infused fluids from the nose, to be directed out of the mouth.
A 1-L bag of sterile saline is hung and connected to one of the stopcocks of the endoscope sheath. Another giving set can be attached to the egress stopcock and allowed to drain into the wet table or into a bucket. The endoscope unit is held in a ‘pistol’ position with the light guide cable pointing toward the ground. Continuous irrigation will help magnify structures as well as remove discharge and haemorrhage that can obscure the view. Control of saline flow is best managed using the control on the ingress port on the sheath.
The operator can collect biopsy using a pair of 3-mm rigid cupped biopsy forceps. These can be placed in a premeasured depth (not to exceed the length measured from the tip of nose to medial canthus of eye). Nasal samples with bone fragments/spicules represent deep sampling technique which is necessary in many cases for an accurate diagnostic interpretation. Samples should be submitted for histopathology (+/- PARR), bacterial culture and sensitivity and aspergillosis culture if indicated.
Haemorrhage is the most common complication of anterior rhinoscopy but is rarely long-lasting or significant. Aspiration of fluid can be prevented by fitting an appropriately sized endotracheal tube and leaving adequate space for the free flow of irrigant fluid over the free edge of the soft palate and out through the mouth.
In conclusion, the author’s experience using rigid endoscopy has provided an easy and rewarding, minimally invasive alternative to traditional diagnostic and surgical interventions for upper respiratory conditions. Endoscopy can be an extremely valuable and versatile part of the clinician’s diagnostic and therapeutic armamentarium.
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