Diagnostic otology (Proceedings)

Non-responsive or chronic and recurrent otitis externa is a common reason for pet owners to leave their regular veterinarian and seek second (and third, fourth and fifth........) opinions. Proper management of these conditions takes a co-ordinated approach that includes strong history taking skills (keeping in mind the primary, predisposing and perpetuating factors involved in otitis), a thorough physical and otoscopic evaluation, appropriate diagnostic tests and the institution of a sound therapeutic plan that addresses the underlying factors while treating the current condition. The problem is that all we have to work with is a little tube on the side of the head!!

Factors related to otitis externa

Primary factors

Primary factors are direct causes of the otitis. They produce inflammation of the ear canal epithelium, and the resultant clinical signs of disease. Examples of primary factors include otodectic otitis, hypersensitivity (including contact allergy), disorders of cornification (e.g. primary seborrhea, sebaceous adenitis), endocrinopathies (e.g. hypothyroidism), immune disorders (e.g. pemphigus), and foreign bodies such as hair or grass awns (or even cotton swabs!).

Predisposing factors

Predisposing factors are those that place the animal at risk for developing disease. Examples of predisposing factors include conformation (pendulous pinnae, stenotic canals), excessive moisture in the ear leading to maceration of tissue (swimming, humidity), obstructive disease (tumours, polyps), systemic disease (pyrexia or other debilitating disease leading to immunosuppression) or inappropriate treatment (use of cotton tipped swabs to clean ears, inappropriate use or choice of topical cleaners, vigorous plucking of hairs from ear canal).

Perpetuating factors

Once the primary causes and predisposing factors work together to change the microenvironment of the ear canal, the perpetuating factors act to prevent rapid resolution of the condition. Examples include bacteria (especially Staphylococcus pseudintermedius and Pseudomonas spp.), yeast (e.g. Malassezia pachydermatis), otitis media (a large percentage of dogs with chronic or recurrent otitis externa have had or have a ruptured tympanic membrane), and progressive pathological changes such as fibrosis, calcification, glandular hypertrophy or hyperplasia and so forth.

The examination

Dermatological exam

A thorough examination of the pet for chronic or recurrent otitis begins away from the ear. Examination of other body regions may alert the clinician to the presence of systemic disease. Be sure to perform a thorough dermatological examination, and look for evidence of self-trauma. Pay particular attention to the paws, the flexor surface of the elbows and carpus, the extensor carpus, axillary and inguinal regions, as they may offer clues to an underlying hypersensitivity. Scaly skin may implicate an endocrinopathy, disorder of keratinization or systemic disease. Primary seborrhea cases may have evidence of comedones in the perineal or ventral tail regions, or keratinous plugs and honey coloured crusts around the nipples.

Otic canal examination

nce the general dermatological examination is complete, examine the pinna for erythema, and swelling. Check the regional lymph nodes. Is there debris in the orifice of the external ear canal? What is its character? Palpate the auricular cartilage for pain, calcification or thickening, and for the typical "clicking" sound associated with fluid in the canal.

The evaluation of the painful ear canal is often the most "challenging" part of the appointment. Don't rodeo! The forced introduction of a scope into the ear canal in the flailing animal just raises the anxiety level (of all involved), is painful, and adds the risk of damage to the canal. However, rapidly and gently collecting a sample for cytology is often doable and it can give you a great deal of information. Before scoping, it may be necessary to treat the ear canal with anti-inflammatory products (e.g. oral prednisone at 1-2 mg/Kg) for a week or two in order to relieve swelling and facilitate visualization of the ear canal. These ears hurt, and the owners will have difficulty placing topical medicaments in the ears unless the patient first gets systemic patient relief, so I will often treat orally for a few days before I start to treat aurally. In some cases, especially if a foreign body is suspected, an appropriate option is sedation and /or anesthesia.

I. Equipment

It is important to use a scope with an excellent light source and good magnification. Plug in models are best to ensure that the battery is well charged. Wall mounting ensures that the scope won't be left unplugged, but the advantage of portability is lost, of course. If prolonged procedures are planned, a permanently plugged in light source is most useful in ensuring adequate lighting for the duration of the operation.

Video-otoendoscopy is certainly more expensive than the hand held devices but is a useful piece of equipment for a busy practice. It has the benefits of magnification and visualization on a video monitor with images that can be saved and printed, allowing clients to see the pathology of the ear canal. Filling the ear canal with saline can further enhance the magnification and keep the tip of the camera lens from fogging. When using this technique, small perforations of the tympanum may sometimes be visualized as air bubbles. It is important that the owner be aware that aggressive flushing has the potential of inducing neurological signs. Indeed, I do not flush cat's ears unless absolutely necessary as this species seem to be very prone to this sequella. Practices that have a video-otoendoscope should also have hand held scopes, as some procedures are still more suited to the hand held devices. Video-otoendoscopy can even be used in the examination room as an educational tool for the owner. Some less expensive hand held video scopes are available for this purpose as well.

CT or MRI are much more expensive imaging techniques, of course, but I feel are much better at evaluating the ear patient than conventional radiography. When involvement of the middle ear is suspected, this technology is useful as an aid in the diagnosis and treatment of otitis media/interna but has the disadvantage of expense and limited availability. CT is particularly useful in evaluation of bony structures. MRI offers better soft tissue resolution than CT but bone or calcification doesn't have the same detail does CT.

II. Routine examination

One should be highly suspicious of an allergic etiology if the pinna and vertical ear canal is affected with the horizontal ear canal and deeper structures being relatively spared. If possible, be sure to examine right to the tympanic membrane (some breed related anatomy and stenosis may make this impossible (think Shar Pei). One must be careful not to over-interpret concave pinnal erythema in the otherwise normal patient. I believe that there is a subset of patients that have the animal version of "white coat syndrome", where the ears get red during times of excitement. A pinnal-pedal reflex can be most informative; ninety five percent of patients with scabies have a positive pinnal pedal reflex but only 80% of patients with a pinnal pedal reflex will have scabies.

There are a few simple rules that even the experienced practitioner forgets with time. Always be sure to evaluate the less affected ear first, and to use two otic specula (one per ear). Multiple duplicate otoscope cones are needed. In one study (Kirby 2010) where, using sterile technique, two cones from each of 50 hospitals were swabbed and submitted for quantitative culture. Twenty-nine percent were contaminated! (6% with Pseudomonas aeruginosa and 4% with Staphylococcus pseudintermedius, among others). Studies have found no growth when the specula are soaked for 20 minutes in Cetylcide® 2% chlorhexidine before cleaning, drying and re-using (Newton, 2006).

It is best if otic examination is performed on a table to allow for proper orientation of the scope. Large dogs can be examined on the floor but the head needs to be held high, often requiring the operator to be kneeling on the floor. The head should be held straight or slightly down, with the assistant holding the muzzle in such a manner as to try to keep the pet from tilting the head (many pets will start to do so as the examination begins, resulting in pain on examination). Visualize the ear canal as you are passing the cone, and gently pull the pinna up and out so as to from the skull while advancing the cone. As the cone is advanced, be sure to avoid the luminal fold, the tissue at the junction of the horizontal and vertical ear canal, as hitting this with the cone head is the most common reason for the pet to object to the exam; once past this point, rotate the handle downward so that the cone approaches a horizontal plane for the visualization of the horizontal ear canal and tympanum

III. Diagnostic testing

     a. Ear swabs for mites.

While ear mites (Otodectes cynotis) can often be seen directly with a good otoscope as small moving dots, treatment is often performed more diligently by the owner once they have observed these mites under the microscope!

Hint: Whenever you are looking for mites, resolution and identification is often improved if you place a cover slip over the sample and turn down the condenser and look for motility. You can also drop the condenser and look for mites on cytology samples (not as accurate but occasionally successful!)

     b. Otic cytology

One of the most useful and cost effective and important diagnostic tests performed on patients with otitis externa is otic cytology. Cytology should be performed at the first visit and repeated at every re-evaluation (normally every two weeks during the initial treatment phase). Samples can be collected with a cotton swab directly from the ear canal or from the end of the otoscope cone. The swab should be advanced as far as the junction of the vertical and horizontal ear canals, whenever possible.

Inflammatory cells may be an important prognostic indicator and should be assessed at each revisit. Remember that while inflammatory cells and acantholytic keratinocytes may support a diagnosis of pemphigus, bacterial infection can also lead to a small number of acantholytic keratinocytes. Rarely, there may be evidence of other pathogenic fungi or neoplastic cells (most commonly squamous cell carcinomas and ceruminous gland tumours).

The presence of organisms is not synonymous with infection. Bacteria or yeast that are noted within the cerumen or on epithelial cells with few inflammatory cells present may be indicative of colonization, not infection. In cases where there are progressive pathologic changes, colonization with microorganisms is not unusual.

Therefore, the finding of bacteria may be indicative of colonization rather than infection in some cases, which may only require topical treatment. This highlights the need for identification (or control) of the underlying etiology, rather than just "killing the bug" as one is tempted to do.

The presence of engulfed bacteria within neutrophils is considered to be strongly suggestive of a bacterial otitis; many of these patients have ruptured tympanic membranes, and a concurrent otitis media. The presence of macrophages suggests that the condition is chronic and erythrocytes imply epidermal ulceration, much more commonly seen with Pseudomonas otitis externa. Pseudomonas infection is more commonly associated with a ruptured tympanic membrane.

The absence of significant findings in the presence of excessive debris or cerumen can also be helpful. This scenario may be seen in atopic patients, or those with food intolerance, primary seborrhea or endocrinopathies

Hint: Try to advance the swab as far as the junction of the horizontal and vertical ear canal (so it is best not to pull on the pinna when performing this procedure). The cytology sample is smeared onto a glass slide. I usually roll the right ear sample on the right side of the slide and the left ear on the left. This way you can compare both ears on the same slide. Heat fix the slides and then stain with Diff-Quik. Small numbers of bacteria and yeast are normal. How many bacteria or yeast is significant? In one study a count per high powered (X 400) field of Malassezia >5 in the dog or bacteria >25 and Malassezia > 12 in the cat or bacteria >15 were considered abnormal. Ask the technician to record the approximate numbers of bacteria, yeast and inflammatory cells for future reference (rather than "bacterial ear infection") and the types of bacteria (cocci, rods etc) and inflammatory cells (PMNs, macrophages) seen. This will allow for comparison of subsequent samples to determine response to therapy or changes that may be made.

     c. Culture and sensitivity

Previous studies have shown that cytology is consistent with culture results in only 68% of the time. Culture will not tell you about the inflammatory response. Therefore bacterial culture should never be considered an alternative to cytology.

Bacterial cultures are warranted in cases where the otitis remains unresolved despite numerous attempts at therapy or when inflammatory cells or large numbers of suspicious bacteria are noted on ear cytology. Remember too, that culture will invariably recover microbes, even in "normal" pets; the ear canals are never sterile. Finally, the results of bacterial culture and sensitivity and minimum inhibitory concentration (MIC) measurement are used to determine the best choice for a systemic antibiotic; indeed, these tests reflect concentrations following systemic treatment rather than direct "bombardment" (nevertheless, it is traditional not to choose antimicrobials that are classified as resistant)

Technique: Cultures are best obtained from the junction of the horizontal and vertical ear canals. Ideally they should be obtained via a sterile otoscope cone. All samples containing rods should be sent for identification. Not all antibiotics of the same class will act similarly on an organism, especially when it comes to the use of quinolones in the treatment of Pseudomonas otitis. Be sure to ask the lab to test the specific antibiotic that you wish to use.

Research at the Ontario Veterinary Clinic (unpublished) suggests that systemic antibiotic therapy may not be at all helpful in the treatment of every case of otitis externa. It has been my personal experience that many of these cases will respond to anti-inflammatory and topical therapy alone. Unrestricted use of antibiotics may indeed contribute to colonization by resistant organisms. Systemic antibiotic therapy is therefore only instituted in our facility if indicated by a poor clinical and cytological response at subsequent re-evaluations. The goal is to encourage the ear canals to 'self-cure', thereby minimizing the development of resistant infections.

     • Bacteria

          o Otitis externa: Common bacterial isolates include Staphylococcus, Pseudomonas, Streptococcus, Proteus, Enterococcus, E. coli, Klebsiella and Corynebacterium.* Malassezia, Staphylococcus and Corynebacterium may be isolated in small numbers in normal ears; however, neither Pseudomonas nor Proteus is routinely isolated from normal ears.*

          o Otitis Media: Middle ear microflora in patients with otitis media: 26.8% Staph pseudintermedius, 23.2% Pseudomonas aeruginosa, 12.8%Beta –hemolytic Strep 11.0% Proteus spp,. 8.5% Staph epidermidis.*

          o Fungal:

          o Malassezia pachydermatis, Candida albicans, Microsporum canis

     • Parasites

          o Accounts for 7% of otitis in dogs and 37% of feral cats; Otodectes cynotis, Demodex, Otobius megnini

     d. Biopsy

Pemphigus is the most frequent autoimmune disease seen involving the ear. The lesions in pemphigus foliaceus are usually pustular and or crusty. Erythematous plaques with scale and alopecia are often the initial lesions seen with vascular diseases, lupus and dermatomyositis. Vascular lesions often progress to a notched, or "punched out" appearance to the pinna at the margins

Biopsy of the pinna can often be a challenging procedure. Ear flaps should only be biopsied under general anesthesia. Be sure to carefully choose the most diagnostic sites and be sure to choose an area devoid of blood vessels. In the case of suspected vascular disease, be careful not to biopsy an ulcer (otherwise, your biopsy report will say "ulcer"). Choosing abnormal areas adjacent to the ulcer are best. In the case of suspected pemphigus, pustules are best biopsied, of course. I generally use a biopsy punch. Lay the punch on the lesion and rotate until you feel cartilage. Some people use saline under the lesion to reduce the risk of puncturing the cartilage; one needs to be careful not to produce an artefact if saline is used. Gently trim the biopsy at the base using iris scissors or a small scalpel blade. I do not usually suture the lesions and let them heal by second intention. Another technique that some practitioners perform is called a shave biopsy, whereby a scalpel blade is used to shave the skin down to but not including the cartilage. As in all skin biopsies, multiple samples should be collected and the samples should be sent to a dermatohistopathologist along with a good history. Clinical photographs are also very helpful.

Tumors

The video-otoendoscope is a very useful tool when it comes to biopsying lesions deeper in the ear canal. Small samples for pathology can be obtained with biopsy forceps that fit through the biopsy channel of the scope. Alternatively, the scope can be used to visualize the mass and the sample can be collected by placing the forceps alongside the scope in the ear canal.

Clients must be advised that most cases of otitis externa require chronic care. Frequent follow-up to monitor progress and repeat cytology is critical. Once the owner understands the need to control rather that cure and to elucidate the underlying cause for many of these conditions, the management will be far simpler and far less frustrating. The institution of a good management program will often keep the pet comfortable, and keep the owner satisfied with the veterinary service

Space limitations for the proceedings did not allow for inclusion of references. However, they are available upon request. Please feel free to email me at dermvet@rogers.com