Otitis Externa in Dogs and Cats

Otitis, encompassing otitis externa and otitis media, is a prevalent condition in canine and feline patients, necessitating a comprehensive understanding of its etiology, clinical presentation, diagnostic approaches, and treatment modalities for effective management.

Otitis Externa

Definition and Overview

• Otitis externa: Inflammation of the external ear canal, often involving secondary bacterial or yeast infections. It is critical to identify and address underlying causes to prevent recurrence and antimicrobial resistance.

• This refers to inflammation of the external ear canal and can result from various factors, including parasitic infestations (e.g., Otodectes cynotis), allergic reactions (such as atopic dermatitis or food allergies), foreign bodies, and underlying dermatological conditions. Secondary infections with bacteria (Staphylococcus intermedius, Pseudomonas aeruginosa) or yeast (Malassezia pachydermatis) are common.

Pathophysiology

• Early signs: Erythema of pinnae and external canal, head shaking, otic discharge (ceruminous or purulent), malodor, swelling, and pain.

• Chronic progression: Stenosis, hyperplasia, fibrosis, and calcification of the canal tissues. Chronic inflammation can result in otitis media.

Primary Causes

1. Parasites:

   • Otodectes cynotis (ear mites): Common in cats (50%) and dogs (5–10%).

   • Demodex spp.: Rare ceruminous otitis externa in dogs and cats.

   • Otobius megnini (spinous ear tick): More common in dogs in southwestern USA.

   • Others: Sarcoptes scabiei, Notoedres cati, Cheyletiella spp., Eutrombicula spp.

2. Foreign Bodies:

   • Common: Plant awns (foxtails), dirt, sand, insects.

   • Consequences: Tympanum rupture and otitis media.

3. Hypersensitivity and Allergic Diseases:

   • Atopic dermatitis: 55% of dogs with atopy have otitis externa; 3–5% present otitis as the sole sign.

   • Food allergies: Up to 80% of affected dogs have concurrent otitis externa; 25% with only otitis.

   • Allergic contact dermatitis (ACD): Rare; reactions to medications or environmental irritants.

4. Keratinization Disorders:

   • Endocrine diseases (e.g., hypothyroidism, hyperadrenocorticism) may result in ceruminous otitis externa.

   • Sebaceous adenitis and idiopathic seborrhea also contribute.

5. Autoimmune Diseases:

   • Rare but include pemphigus foliaceus, discoid lupus erythematosus, and bullous pemphigoid.

   
   

Predisposing Causes

1. Anatomic Factors:

   • Breeds with long pendulous ears, stenotic ear canals, or excessive hair (e.g., Cocker Spaniels, Poodles).

2. Moisture:

   • Frequent swimming or bathing disrupts the protective ear barrier, promoting infections.

3. Iatrogenic Factors:

   • Trauma (e.g., swabs), irritating solutions, and inappropriate treatments.

4. Obstructive Diseases:

   • Inflammatory polyps or tumors prevent drainage, predisposing to infections.

Perpetuating Causes

1. Bacteria:

   • Opportunistic pathogens: Staphylococcus intermedius, Pseudomonas aeruginosa, Proteus mirabilis, etc.

   • Chronic cases often involve resistant Pseudomonas strains.

2. Yeast:

   • Common: Malassezia pachydermatis, occasionally Candida spp.

3. Otitis Media:

   • Often secondary to otitis externa through tympanic membrane rupture.

4. Pathologic Changes:

   • Chronic inflammation leads to fibrosis and mineralization.

Clinical Evaluation

1. History:

   • Detailed dermatologic and general history (e.g., swimming, other infections, allergy signs).

2. Physical Examination:

   • Assess ear canal erythema, discharge, and ulceration.

   • Check for concurrent skin lesions to identify systemic diseases.

3. Diagnostic Tests:

   • Skin scrapings (e.g., rule out demodicosis).

   • Cytology and culture for bacterial and fungal pathogens.

   
   

Clinical Presentation

• Otitis Externa: Clinical signs include ear scratching, head shaking, erythema of the ear canal, otic discharge (which may be ceruminous or purulent), malodor, and pain upon palpation. Chronic cases may exhibit canal stenosis, hyperplasia, and fibrosis.

Diagnostic Evaluation

1. History and Physical Examination: A thorough history and otoscopic examination are essential to assess the ear canal and tympanic membrane integrity.

2. Cytology: Sampling of ear canal exudate aids in identifying infectious agents, such as bacteria or yeast.

3. Imaging: Advanced imaging techniques like computed tomography (CT) or magnetic resonance imaging (MRI) are valuable for evaluating the extent of middle ear involvement, especially in chronic or refractory cases.

4. Culture and Sensitivity: Particularly indicated in chronic or recurrent cases to guide targeted antimicrobial therapy.

Treatment Strategies

• Cleaning: Regular and thorough cleaning of the ear canal is crucial to remove debris and exudate, facilitating the effectiveness of topical treatments. This may require sedation or anesthesia in uncooperative patients.

• Topical Therapy: The selection of appropriate topical agents should be based on cytological findings:

  • Antibacterial agents for bacterial infections.

  • Antifungal agents for yeast infections.

  • Anti-inflammatory agents to reduce canal inflammation and discomfort.

• Systemic Therapy: Indicated in cases of otitis media or when topical treatment is insufficient:

  • Antibiotics based on culture and sensitivity results.

  • Analgesics and anti-inflammatory medications to manage pain and inflammation.

• Surgical Intervention: Procedures such as myringotomy for middle ear drainage or total ear canal ablation (TECA) may be necessary in cases unresponsive to medical management or with severe structural changes.

Preventive Measures and Owner Education

• Regular Ear Cleaning: Educate owners on proper ear cleaning techniques using veterinarian-recommended solutions to maintain ear health and prevent recurrence.

• Address Underlying Conditions: Management of predisposing factors, such as allergies or endocrine disorders, is essential to prevent chronic otitis.

• Follow-Up: Regular re-evaluations are crucial to monitor treatment efficacy and make necessary adjustments.

In conclusion, otitis in dogs and cats is a multifactorial condition requiring a systematic approach to diagnosis and treatment. Early identification and management of underlying causes, combined with appropriate therapeutic interventions, are key to successful outcomes.

References and Links:

• Rosser, E. J. (2004). Causes of otitis externa. Vet Clin Small Anim, 34(4), 459–468.

• Veterinary Partner. Otitis Externa Treatment in Dogs and Cats.

• AVMA Publications. Managing recurrent otitis externa in dogs: what have we learned and what can we do better?