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Otology in the dog and cat: a clinician's approach

by
01 August 2014, at 1:00am

Jayne Laycock reports on her pick-of-the- month webinar on The Webinar Vet, this one on otology in the dog and cat presented by Dr Klaus E. Loft of Angell Animal Medical Center in Boston.

WITH grass seed season upon us, cases of acute onset otitis externa will start to ood through the door, and most of the time the problem is easily solved by removal of the offending foreign body.

Unfortunately, treating cases of chronic or recurring ear disease is not always that simple and can sometimes be the source of a client’s discontent when this seemingly simple issue (in the eyes of the client) just won’t go away.

The Webinar Vet organised Dr Klaus Loft to lead a webinar covering otology in the dog and cat discussing how we approach and best manage these cases. Dr Loft, of Angell Animal Medical Center (MSPCA) in Boston, has published articles and lectured both in Scandinavia and the United States; his special interests are feline dermatology and chronic ear disease.

He wanted to emphasise rstly that a patient showing ear disease is always a dermatology case until proven otherwise, and a full case history is absolutely key in deciphering whether these patients have ever suffered any previous dermatological episodes. Dr Loft also stressed the importance of performing a full clinical hands-on examination.

The pinnae should be checked thoroughly, the temporomandibular joint should be manipulated for signs of pain and the cranial nerve re exes assessed. A thorough otoscopic examination is essential using good equipment.

At this stage Dr Loft expressed concern that many cases referred to him will often not mention being either able or unable to visualise the tympanic membrane. He believes that in 20- 30% of his own cases he is unable to visualise the tympanic membrane (perhaps there is wax in the way or the dog won’t tolerate full examination) and it is always imperative that we note this down for comparative reasons at a re-check.

The three Ps

When considering how to best approach otology cases, Dr Loft explained that we needed a good understanding of the three Ps affecting ear disease: predisposing factors, primary factors and perpetuating factors.

  • Predisposing factors 

Predisposing factors are conditions that facilitate and increase the risk of inflammation within the ear canal. Anatomy and confirmation fall under this category with breeds like the Shar Pei suffering from marked stenosis of the ear canals.

Pendulous ears in dogs such as the Basset hound are also a predisposing factor but Dr Loft believes they are not a causal factor for developing inflammation in the ear, but once inflammation has developed, this particular design is likely to increase the severity of the problem.

He also discussed damage to a mechanism known as epithelial migration which could also be a predisposing factor. This mechanism consists of a mixture of cellular glands within the ear canal which grow upwards from the tympanic membrane as a conveyor belt of cells.

In people, if this “conveyor belt” is damaged, perhaps by excessive use of ear buds, ear wax will be less effectively removed, increasing the risk of inflammation. Although not proven, Dr Loft believes this may also be a problem in dogs potentially caused by trauma such as hair plucking (a practice Dr Loft does not recommend) or just by us traumatising the ear canal with an otoscope.

Other predisposing factors include obstructive disease such as benign and malignant neoplasia as well as keratinisation defects such as sebaceous adenitis, and iatrogenic causes such as “swimmer’s” ear. 

  • Primary factors 

Primary factors are conditions which initiate inflammation of the ear canal. Cutaneous adverse food reaction and atopic dermatitis fall under this category. Usually these cases will have a history of multiple recurring episodes of otitis externa and most will have bilateral disease. 

According to Dr Loft there is an 80% incidence of otitis externa in cases of cutaneous adverse food reaction and is seen as a single entity with no other clinical signs in 24% of these cases. In comparison, there is a 50-80% incidence of otitis externa in dogs suffering from atopy and is only seen as a single entity in 5-10% of these cases.

Other primary factors include foreign bodies and parasites such as Otodectes. Dr Loft also explained that demodicosis can cause otitis externa, and he recommended to always consider this parasite especially if a case worsens after use with topical steroids. Immune- mediated disease such as pemphigus complex, especially in the cat, puppy strangles and erythema multiforme are also primary factors.

  • Perpetuating factors 

Perpetuating factors maintain or worsen inflammation within the ear canal of which over-treatment and under-treatment are two of the main culprits.

Over-treatment such as over-use of an ear cleaner can lead to an excess of moisture within the ear canal and could cause mechanical trauma.

Under-treatment, however, is the biggest reason for failure in managing cases of otitis. Drugs may not have been administered for long enough and in many cases we may just be under- dosing.

Dr Loft explained the total length of an ear canal can be up to 5 or 7.5cm, especially in breeds such as the Basset hound. This is a lot of “skin” that we need to treat and the standard 4-5 drops administered topically may just not be enough.

Owner compliance is also key and Dr Loft will often get owners to administer drops twice daily just to ensure compliance, even though more frequent administration may be preferable.

Secondary bacterial and fungal infections are also significant perpetuating factors and Dr Loft recommends always performing cytology in any case of ear disease. 

He advises using Q tips to obtain the sample and this should be done prior to any manipulation of the ear canal. Fungi, rods, cocci, inflammatory cells and intra-cellular bacteria should all be looked for under microscopy after performing a Diff Quick stain.

He also recommends treating as a bacterial otitis if you see four or more cocci per high-power eld (phpf) and/or one or more rod phpf. He recommends treating as a fungal otitis if you see two to three or more yeast phpf.

On seeing inflammatory cells, Dr Loft always recommends using an anti- inflammatory. He generally considers performing a culture and sensitivity if, after treating according to the cytology results, rods are still present on repeat cytology or are continuing to increase and could raise suspicion of a pseudomonas infection.

Culture and sensitivity is also necessary in cases of otitis media so these cases can be treated systemically.

Principles of treatment

Treatment of otitis externa using topical medication is usually all that is necessary in most first line cases. The use of cleaners to remove debris and also alter pH is useful as well as the topical administration of anti-fungals, antibacterials and anti-inflammatories according to the cytology results.

Once again Dr Loft wanted to emphasise the point that the size of the ear canal needed to be considered when deciding on an appropriate dose of topical medication.

He recommends administering 2-4 drops in the cat, 8 drops in the small dog, 10-15 drops in the medium to large dogs and 20 drops in the ears of dogs such as the Basset hound. For compliance reasons Dr Loft recommends administering these doses twice daily.

He uses systemic treatments in less than 10% of first line cases but uses it in almost all of his chronic cases. The use of glucocorticoids to reduce inflammation and open up the ear canal is key and Dr Loft uses these at a dose of 0.5mg/kg every 12 hours in dogs and 1mg/kg every 12 hours in cats.

He has also found oral cyclosporine useful where there are chronic proliferative changes, although it only tends to be of bene t in 20-25% of cases.

He always uses systemic treatment in cases of otitis media and where there has been evidence of tympanic membrane rupture, although he warned us that tissue penetration is unlikely to be very good.

Summary

Dr Loft’s webinar was an excellent insight into how we can best manage ear disease by considering the broader issues around this condition.

For example, the anatomy of the ear needs to be taken into account when considering how much medication to administer and, as for skin, any underlying factors such as allergic skin disease need to be addressed.

This was a thought-provoking webinar which looked at ear disease from a different angle compared to other forms of CPD I have encountered on this subject matter and is well worth an hour of your time.