Canine Otitis Externa and Otitis Media Study Guide

Overview and Clinical Importance

Otitis externa is an inflammatory condition of the external ear canal affecting approximately 10-20% of canine patients presenting to veterinary practices. It represents one of the most common dermatological complaints in dogs and is a frequent topic on the NAVLE. Understanding the multifactorial nature of otitis, including primary causes, secondary infections, predisposing factors, and perpetuating factors (PSPP classification), is essential for successful diagnosis and management.

Otitis media (middle ear inflammation) occurs in 50-89% of dogs with chronic otitis externa and significantly complicates treatment. Foreign bodies, particularly grass awns (foxtails), represent an important primary cause of acute, often unilateral, otitis that requires prompt identification and removal.

Anatomy of the Canine Ear

External Ear

The canine external ear consists of the pinna (auricular cartilage) and the external ear canal. The ear canal is L-shaped, composed of a vertical canal (approximately 2.5 cm long, runs ventrally from the pinna opening) and a horizontal canal (extends medially at approximately 75-degree angle to the tympanic membrane).

The ear canal is lined by skin containing sebaceous glands, ceruminous (apocrine) glands, and hair follicles. The cerumen produced provides a protective barrier and has antimicrobial properties. Epithelial migration from the tympanic membrane outward serves as a natural self-cleaning mechanism.

Tympanic Membrane

The tympanic membrane (eardrum) is positioned at a 45-degree angle to the horizontal canal axis. It is semitransparent and divided into the pars flaccida (small, dorsal, pink, loosely attached portion) and the pars tensa (larger, gray, semitransparent ventral portion). The manubrium of the malleus is visible through the tympanic membrane as a white, L-shaped structure.

Middle Ear

The middle ear consists of the tympanic bulla (air-filled cavity), three auditory ossicles (malleus, incus, stapes), and the auditory (Eustachian) tube. Important structures in proximity include the facial nerve (CN VII - damage causes facial paralysis), sympathetic nerves (damage causes Horner syndrome), and vestibular apparatus (involvement causes head tilt, nystagmus, ataxia).

PSPP Classification System

The PSPP classification provides a systematic approach to understanding the multifactorial nature of otitis. Successful management requires identifying and addressing factors in all categories.

Clinical Presentation

Clinical Signs of Otitis Externa

Signs Suggesting Otitis Media

• Chronic/recurrent otitis externa (greater than 6 months)
• Poor response to appropriate topical therapy
• Neurological signs: head tilt, vestibular ataxia, nystagmus
• Facial nerve paralysis: lip droop, inability to blink
• Horner syndrome: miosis, ptosis, enophthalmos
• Pain when opening mouth

Diagnostic Approach

Ear Cytology - The Most Important Test

Cytology is the single most informative diagnostic test for otitis. Perform on ALL cases and at every recheck to monitor response to therapy.

Sample Collection

• Insert cotton swab to horizontal canal junction
• Sample BOTH ears separately
• Roll swab onto glass slide
• Stain with Diff-Quik
• Examine 1000x (oil immersion) for bacteria; 400x for yeast

Cytology Interpretation

Foreign Bodies: Grass Awns (Foxtails)

Grass awns (foxtails) are barbed seed heads that migrate forward through tissues. They are a common primary cause of acute, often unilateral, otitis externa.

Clinical Presentation

• Sudden onset head shaking (often violent)
• Usually UNILATERAL (bilateral suggests other cause)
• Head tilt toward affected side
• History of outdoor activity in grassy areas
• Seasonal: late spring through fall

Treatment

• Removal with alligator forceps under direct visualization
• Sedation/anesthesia often required
• Ensure complete removal (partial allows continued migration)
• Treat secondary infection based on cytology

Ear Mites (Otodectes cynotis)

Otodectes cynotis is a surface mite causing highly contagious ear disease. More common in cats, but important in puppies and strays.

• Characteristic discharge: Dark brown/black, dry, crumbly, "coffee ground" appearance
• Intense pruritus, usually bilateral
• Diagnosis: otoscopy (white moving specks) or microscopy

Treatment Options

• Selamectin (Revolution) - single topical dose often effective
• Sarolaner (Simparica) - oral, label-approved
• Fluralaner (Bravecto) - oral/topical
• Ivermectin - avoid in MDR1-positive breeds

Key Point: TREAT ALL IN-CONTACT ANIMALS for at least 6 weeks to cover the entire life cycle. Ear mites are highly contagious between dogs and cats.

Treatment of Otitis Externa and Media

Treatment Principles

• Identify and treat PRIMARY cause
• Treat SECONDARY infections based on cytology
• Address PERPETUATING factors
• Modify PREDISPOSING factors where possible
• Regular recheck with CYTOLOGY to confirm resolution

Topical Antimicrobial Selection

Systemic Therapy Indications

• Otitis media (documented or suspected)
• Severe canal ulceration
• Severe stenosis preventing topical penetration
• Pseudomonas not responding to topical therapy

Fluoroquinolones (enrofloxacin 10-20 mg/kg q24h) are first-line for Pseudomonas. Treatment duration for otitis media: 4-6 weeks minimum, continued 7-10 days past clinical resolution.

Surgical Management

Total Ear Canal Ablation with Bulla Osteotomy (TECA-BO) is indicated for end-stage otitis when: severe irreversible canal stenosis/calcification, chronic otitis media unresponsive to medical management, neoplasia, or severe pain with poor quality of life. Results in deafness on affected side.