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Diagnostic approach to dogs with otitis externaOtitis externa in the dog is a very common clinical presentation and one of the most common diseases in the dog that lead to a visit to the veterinary practice (Hill et al, 2006). Otitis can be a very painful condition, which often recurs due to failure to identify and successfully treat the underlying disease. This article is part of a series of reviews on different aspects of ear disease and discusses the diagnostic approach to cases of otitis externa.

Key words: otitis externa, primary disease, perpetuating disease, predisposing disease, ear cytology, otoscopy

IntroductionMany dogs are presented to first opinion and referral veterinary dermatology prac-titioners with ear disease (Hill et al, 2006). This condition can be chronic and/or relapsing and frustrating to treat. In order to provide best patient care, it is important to have a thorough approach to each case presenting with this painful and common clinical condition. August (1988) sug-gested a system describing the P(rimary), P(redisposing) and P(erpetuating) factors implicated in otitis and all of these factors need to be carefully addressed to achieve a positive outcome for the dog, owners and ultimately also the veterinary surgeon.

Primary factorsPrimary factors can cause otitis in a normal ear. As the ear canal is lined with skin, which is only slightly modified compared to haired skin, generalised dermatitis can be the primary cause of otitis. Allergic diseases (atopic dermatitis, adverse cutaneous food reactions, flea allergic dermatitis) (Figure 1), hormonal diseases (e.g. hyperadrenocorticism, hypothyroidism), keratinisation disorders (e.g. primary seborrhoea, sebaceous adenitis etc), parasitic diseases (e.g. ear mites, Demodex spp. and ticks), and autoimmune diseases are examples. In localised and particularly unilateral disease, foreign bodies and neoplasia are more likely underlying problems but more generalised skin disease cannot be ruled out. Saridomichelakis et al (2007) found allergic dermatitis (43%), grass awns (12%) and otoacariasis (7%) to be the most common primary factors.

Predisposing factors Certain factors that are present before the problem begins, can predispose to ear disease, such as the conformation of

Ariane Neuber DrMedVet CertVD DipECVD MRCVS RCVS & European Specialist in Veterinary Dermatology

Ariane spent some time in general practice before specialising in dermatology. She has many years of experience in referral dermatology. After an internship at the Animal Health Trust in Newmarket, she completed her 3-year residency at Edinburgh University and gained her CertVD, DECVD and Royal College Specialist Status as a result.

She currently provides a dermatology referral service at:Davies Veterinary Specialists in Higham Gobion (Bedfordshire) Tel: 01582 883950

Chiltern Referral Services in Chalfont St Giles (Buckinghamshire) Tel: 01494 875 875

Active Vetcare Referrals in Maidenhead (Berkshire) Tel: 01628 628121

www.derm4pets.co.uk

the pinnae (Figures 2a-c), e.g. floppy ears in setters, spaniels etc; narrow ear canals, e.g. in Shar peis; hairy ears, e.g. Poodles and Cocker Spaniels (Stout-Graham et al, 1990), unsuitable treatments, e.g. frequent cleaning with a harsh cleaner (Figure 3) or the use of ear buds; or lifestyle factors, e.g. frequent swimming. However, on their own and without an underlying condition, these factors do not necessarily cause ear disease.

Perpetuating factors Perpetuating factors include changes that are caused by the ear disease itself and make the disease more likely to persist, such as stenosis due to swelling of the lining of the ear canal, otitis media (Figure 4), ceruminous gland hyperplasia, increased humidity, excessive discharge, dysfunction of the epithelial migration, calcification of the ear canals, debris in the middle ear or a dilated or ruptured tympanic membrane. August (1988) also classified organisms such as bacterial cocci and rods and yeast in this category. However, more recently, Griffin has reclassified bacteria and yeast as second-ary factors along with drug reactions and overcleaning of the ears. This system is currently referred to as PSPP.

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P - primary factorsS - secondary factors P - predisposing factorsP - perpetuating factors

Clinical signsDogs with otitis can present with a varia-tion of several clinical signs including otic pruritus/irritation, malodour, headshaking, otic discharge, head tilt, aural haematoma, painful ears, inability to chew hard food due to pain and erythema. In mild cases owners may be unaware of the problem.

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Figure 1: Typical mild otic erythema in a dog with atopic dermatitis

Figure 3: Overzealous cleaning leaving irritated lining of the ear canal and white creamy debris

Figure 4: Tear in tympanic membrane in a dog with otitis externa and media. Otitis media can be a perpetuating factor in ear disease

Figure 2: Different conformations of pinnae. A: erect; B: pendulous. C: hairy. Hairy and pendulous pinnae can be predisposing factors for otitis

Figure 2A

Figure 2C

Figure 2BSignalmentThe age and breed in particular can be valuable items of information in terms of making a diagnosis in cases of otitis (Table 1). Ear mites are more common in young dogs and possibly in certain breeds, e.g. Cocker Spaniels (Cristina, 2007). Neoplasia on the other hand is more common in older patients, particularly if they suffer from unilateral disease and have never had any ear or skin problems previously.

Adult dogs are more likely to develop allergies, with one to three years the most common age at onset, but dogs from six months onwards are certainly being seen on a regular basis.

The importance of ear conformation has been discussed and the breed is therefore also important. Many breed predispositions exist for diseases such as atopic dermatitis as a possible primary factor.

HistoryTaking a thorough history is a very important part of the investigation of all dermatological cases and cases of otitis externa are no exception (Table 2). Important aspects include the owner’s complaint, lifestyle (e.g. swimming), progression of the disease (acute, gradual, chronic, relapsing), other medical issues; particularly skin problems elsewhere, seasonality, prior treatments, eating habits and tests that have already been performed.

In terms of clinical signs, owners often complain about head shaking, foul odour, discharge, excessive scratching of the ears and pain when touching the ears.

Young Young adult Older

Ectoparasites

Dermatophytosis

Congenital diseases

Immune-mediated dermatoses

Allergies (75% of atopic dermatitis 6 months to 3 years old)

Immune-mediated dermatoses

Keratinisation defects

Follicular dysplasias

Metabolic diseases

Neoplasia

Endocrinopathies

• Have you seen any headshaking or scratching?

• Have you noticed any discharge from the ears?

• Do other pets lick the patient’s ears?• Do you use any ear cleaner/drops or

powders?• Are the ears malodorous?• What was the first thing you noticed?• Is your pet itchy elsewhere?

If so, how itchy?• Is this the first episode of ear

problems?• Is your dog very clean, e.g. does it lick

its paws?• Has your pet any other health issues

e.g. increase/loss of appetite, thirst and exercise tolerance; vomiting/diarrhoea?

Table 1 – Signalment: The influence of age on the diagnosis

Table 2: Useful questions to ask when taking a history

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