Stop Treating the Ear Alone: Finding the Primary Cause Behind Recurrent Canine Otitis

A dog presents with its third ear infection in six months.

The cytology reveals cocci and Malassezia, and the owner says, "The last ear drops worked, but the infection came back."

The question isn't "Which ear drops should I prescribe now?"

It's "Why did the infection return in the first place?"

This shift in thinking is what separates successful long-term management from the frustrating cycle of treating recurrent otitis.

Infection Is Usually the Consequence—Not the Cause

Bacteria and yeasts are often blamed for chronic otitis, but they rarely initiate the disease. Instead, they take advantage of an inflamed and unhealthy ear canal. Every recurrent otitis case should prompt clinicians to investigate the underlying condition that altered the ear canal environment rather than focusing solely on eliminating microorganisms¹.

Without addressing the primary trigger, recurrence is highly likely despite appropriate antimicrobial therapy.

Use the PSPP Framework for Every Recurrent Case

A practical approach to recurrent otitis is the Primary–Secondary–Predisposing–Perpetuating (PSPP) framework. This helps clinicians identify not only what is growing in the ear today but also why the disease keeps returning^1,2.

Primary factors – What started the inflammation?

Primary factors directly initiate inflammation in an otherwise healthy ear canal.

Common examples include:

• Atopic dermatitis
• Adverse food reactions
• Ear mites (Otodectes cynotis)
• Foreign bodies
• Endocrine disorders such as hypothyroidism
• Immune-mediated skin diseases

Among these, allergic skin disease is the most common primary cause of recurrent canine otitis, with otitis often being the first or only clinical sign in some dogs^1,3.

If a dog experiences repeated bilateral ear infections with no obvious trigger, allergy should always be high on the list of differential diagnoses.

Secondary factors – What is complicating the disease?

Once inflammation develops, opportunistic microorganisms readily colonize the ear canal.

Common secondary pathogens include:

• Staphylococcus pseudintermedius
• Malassezia pachydermatis
• Pseudomonas aeruginosa
• Proteus species

These organisms require appropriate treatment, but eliminating them alone rarely prevents recurrence if the primary disease remains uncontrolled¹.

Predisposing factors – Why is this ear vulnerable?

Predisposing factors do not directly cause otitis but increase the likelihood of disease by altering the ear canal environment.

Examples include:

• Pendulous ears
• Narrow ear canals
• Excess hair within the ear canal
• Frequent swimming
• High environmental humidity
• Ear canal masses or polyps
• Excessive or traumatic ear cleaning

Breed also plays an important role. The VetCompass study identified breeds such as Basset Hounds, Chinese Shar-Peis, Labradoodles, Beagles, Golden Retrievers, Cockapoos and Cocker Spaniels as having a significantly higher risk of developing otitis externa than crossbred dogs³.

Perpetuating factors – Why won't it heal?

Chronic inflammation eventually remodels the ear canal, making successful treatment increasingly difficult.

Common perpetuating factors include:

• Ear canal stenosis
• Glandular hyperplasia
• Fibrosis
• Tympanic membrane damage
• Otitis media
• Biofilm formation

Once these changes occur, simply switching antibiotics is unlikely to resolve the disease. Advanced diagnostics, aggressive medical therapy or referral may be required¹.

Don't Miss the Clues Outside the Ear

Many underlying diseases leave subtle clues elsewhere on the patient.

During every recurrent otitis consultation, perform a complete dermatological examination rather than focusing only on the ears.

Look for:

• Paw licking
• Facial rubbing
• Generalised pruritus
• Ventral erythema
• Recurrent pyoderma
• Seborrhoea
• Alopecia
• Weight gain or lethargy suggestive of endocrine disease

In many dogs, the ear infection is simply the first visible manifestation of a broader dermatological disorder^1,2.

Ask Better Questions During History Taking

The history often provides the biggest clue to the underlying diagnosis.

Useful questions include:

• Is this the first episode or has it happened repeatedly?
• Is it seasonal?
• Does the dog swim regularly?
• Are one or both ears affected?
• Does the dog itch elsewhere?
• Has a food elimination trial been performed?
• Which previous treatments worked, and for how long?

These answers frequently point towards allergy, environmental factors or incomplete resolution of previous episodes.

Treat the Disease, Not Just the Cytology

Ear cytology remains one of the most valuable diagnostic tools in practice because it identifies the organisms currently present and guides topical therapy¹.

However, cytology answers only one question:

"What is growing today?"

It does not explain why those organisms became dominant.

Successful management combines cytology with:

• Complete dermatological examination
• Thorough otoscopic evaluation
• Assessment of the tympanic membrane
• Review of previous treatment history
• Investigation for allergic, endocrine or anatomical disease where appropriate

Only then can clinicians move beyond treating individual infections to preventing recurrence.

Clinical Pearl

If a dog has received multiple courses of topical antimicrobials yet continues to return with otitis, resist the temptation to prescribe another ear medication immediately.

Instead, ask:

"What primary disease have I not identified yet?"

Finding and managing that underlying cause is often the key to long-term clinical success.

Key Takeaways

Recurrent otitis is usually a manifestation of an underlying disease rather than a primary infection. It is recommended to use the Primary–Secondary–Predisposing–Perpetuating (PSPP) framework to investigate every chronic or recurrent case. Allergy remains the leading primary cause of recurrent canine otitis. Ear cytology guides treatment but does not identify the underlying reason for recurrence. Long-term success depends on treating both the infection and the primary disease.

References

1. Bajwa J. Canine otitis externa—Treatment and complications. Can Vet J. 2019;60(1):98–101. PMID: 30651659. PMCID: PMC6294027. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC6294027/
2. O'Neill DG, Volk AV, Soares T, Church DB, Brodbelt DC, Pegram C. Frequency and predisposing factors for canine otitis externa in the UK: a primary veterinary care epidemiological view. Ir Vet J. 2021;74:16. DOI: 10.1186/s40575-021-00106-1. Available from: https://irishvetjournal.biomedcentral.com/articles/10.1186/s40575-021-00106-1
3. Hoff S. Otitis externa in animals. MSD Veterinary Manual. Updated 2025. Available from: https://www.msdvetmanual.com/ear-disorders/otitis-externa/otitis-externa-in-animals