Etiology

• Primary Causes: These factors create disease in a normal ear, often altering the ear environment and leading to secondary infections. Primary causes include:

  • Allergies: Adverse food reactions, atopic dermatitis, or contact allergies.

  • Parasites: Mites like Otodectes, Demodex, and Sarcoptes.

  • Autoimmune/Immune-mediated disorders: Conditions like pemphigus foliaceus, vasculitis.

  • Endocrine diseases: Hypothyroidism and hyperadrenocorticism (Cushing’s disease).

  • Epithelialization disorders: Sebaceous adenitis, zinc-responsive dermatitis.

  • Foreign bodies in the ear canal.

  • Glandular disorders: Sebaceous gland hyperplasia.

  • Fungal infections: Such as Aspergillus species.

  • Viral infections: Distemper virus.

  • Miscellaneous causes: Proliferative necrotizing otitis (cats), juvenile cellulitis.

• Secondary Causes: These occur in an already abnormal ear, often in chronic otitis externa cases when primary causes are unaddressed. Secondary causes include:

  • Bacterial infections: Staphylococcus, Streptococcus, Pseudomonas, etc.

  • Yeast overgrowth: Malassezia species.

  • Medication reactions or overcleaning of the ear.

• Predisposing Factors: Conditions that increase the risk of developing otitis externa, including:

  • Ear canal anatomy: Pendulous pinna, stenotic (narrow) ear canals, excessive hair.

  • Excess moisture: From swimming or a humid environment.

  • Obstructive ear disease: Tumors, polyps, cysts, or other blockages.

  • Systemic diseases: Immune suppression or catabolic states.

  • Ear trauma: From treatments or cleaning.

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Clinical Signs 

• Common Signs:

  • Head shaking or rubbing the ear.

  • Pain when touching or manipulating the ear.

  • Odor from the ear, often foul-smelling.

  • Discharge from the ear, which may be purulent (pus-filled), waxy, or dark.

  • Redness (erythema), swelling, or thickening of the ear canal.

  • Erosion or ulceration of the ear canal or pinna.

  • Hyperplasia (thickening) of the glandular tissue inside the ear.

• Painful Cases: In severe or chronic cases, the ear may be painful to the touch, requiring sedation for further examination.

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Diagnosis 

• History & Physical Examination: The diagnosis starts with a thorough history (e.g., underlying diseases, symptoms) and a physical examination, including palpation of the ear canal and pinna to assess swelling, pain, or abnormal tissue changes.

• Otoscopic Examination: The ear canal is evaluated using an otoscope to check for:

  • Stenosis, erythema, ulceration, or exudate.

  • Tympanic membrane: Should be checked for damage, rupture, or infection.

• Cytology: A sample of ear discharge or exudate is taken and examined under a microscope to identify:

  • Bacterial infections (e.g., Staphylococcus, Pseudomonas).

  • Yeast infections (Malassezia).

  • Mites (e.g., Otodectes cynotis in cats).

  • Inflammatory cells (e.g., neutrophils, WBCs).

• Advanced Diagnostics:

  • Culture and Sensitivity: Culturing the exudate may be necessary to identify resistant bacteria (e.g., Pseudomonas).

  • Radiography or Imaging: X-rays or CT scans may be required if middle ear disease or tympanic membrane rupture is suspected.

• Additional Tests:

  • Skin Scrapes: For identifying parasites such as Demodex or Sarcoptes.

  • Biopsy: If a mass or growth is suspected inside the ear canal.

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Treatment

• Initial Management: The first step is to control pain and inflammation with glucocorticoids (e.g., prednisone, triamcinolone). These help reduce swelling, pain, and itching, making it easier for owners to clean the ears at home.

• Ear Cleaning:

  • The ear canal should be cleaned, especially if there is a buildup of wax or pus.

  • A ceruminolytic solution (e.g., carbamide peroxide) can be used, especially if the material is thick.

  • Use mild, neutral-pH cleaners for inflamed ears to avoid further irritation.

  • Ear plucking and hair clipping may be necessary to facilitate cleaning.

• Topical Therapy:

  • Most treatments combine antibiotics, antifungals, and glucocorticoids.

  • The choice of medication is based on cytology results to identify the specific organism causing the infection (e.g., bacterial or fungal).

  • Topical antimicrobials: Infected ears may require aminoglycosides, fluoroquinolones, or polymyxin B for bacterial infections. Antifungals like ketoconazole can be used for yeast infections.

• Systemic Therapy:

  • Oral antibiotics or systemic antifungals may be required for severe or recurrent cases.

  • Systemic glucocorticoids (e.g., prednisone) may also be prescribed for inflammation control.

• Chronic Otitis Externa: In cases where otitis externa is unresponsive to treatment, further diagnostic workups, including imaging and culture, may be necessary. Otitis media (middle ear infection) should be suspected and treated accordingly, possibly requiring surgical intervention.

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Prevention

• Ear Hygiene: Regular ear cleaning should be part of preventive care, especially for animals with a history of ear infections. The frequency of cleaning can be reduced over time, from daily to once or twice weekly, depending on the animal’s needs.

• Drying Ears: Keep ears dry and well-ventilated. For dogs that swim frequently, topical astringents can be used to prevent excess moisture accumulation in the ear canal.

• Avoiding Water: Prevent water from entering the ear canal during bathing and swimming, as it can lead to maceration (softening of the skin), which impairs its barrier function and predisposes to infection.

• Hair Management: Clipping excessive hair around the ears and ear canal, especially in animals with floppy ears or hairy ear canals, improves ventilation and reduces moisture buildup. However, hair removal should be done carefully to avoid causing irritation or inflammation.

• Owner Education: Teaching owners how to clean their pet’s ears properly and ensuring they follow through with the prescribed treatments are crucial for successful management. Regular follow-ups are recommended to monitor the infection and adjust treatment as necessary.

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Prognosis

• Acute Otitis Externa: In most cases, with appropriate treatment, acute otitis externa resolves within 2–4 weeks.

• Chronic Otitis Externa: Chronic or recurrent otitis externa may take several months to resolve and may require long-term management. Some animals may need maintenance treatments to control flare-ups.

• Complications: If left untreated or improperly managed, otitis externa can progress to more severe conditions, including otitis media (middle ear infection) or tympanic membrane rupture, which can cause hearing loss or other complications.

• Chronic and Refractory Cases: Cases with resistant infections (e.g., Pseudomonas or MRSA) may require more aggressive treatments, including long-term topical therapy, systemic medications, and possible surgery (e.g., total ear canal ablation) in severe cases.