Dermatology: KEY STRATEGIES to Otitis Externa Management

Written by Christina Restrepo, DVM, DACVD

Animal Specialty Hospital of Florida, Naples, FL, USA

Introduction

1. Otitis externa (OE) is the inflammation of the external ear canal lining, which can also involve the pinna(e). It is one of the most common conditions seen by small animal veterinarians, representing as much as 10 to 20% of canine cases and 2-8% in feline patients.
2. OE results from a combination of factors that alter the physical and microbiological state of the ear canal such that inflammation and infection occur in a somewhat vicious cycle.
3. The underlying cause [ie. predisposing factors, primary factors, and perpetuating factors] for OE must be evaluated or the condition is likely to become chronic resulting in irreversible pathologic changes, pain, and owner frustration.
4. Common clinical signs of otitis externa include otic pruritus, pain, and malodorous exudate. Head/ear rubbing, ear scratching, head shaking, aural hematomas, and a head tilt (affected ear tilted down), may be noted. In acute cases, the concave pinna and otic canal are usually erythematous. The ear canal may also be swollen, eroded or ulcerated. Pinnal alopecia, excoriations, and crusts can ensue. Depending on the underlying cause, concurrent skin disease may be seen. In chronic cases, pinnal hyperkeratosis, hyperpigmentation, and lichenification, as well as ear canal stenosis from fibrosis or ossification, are common. Decreased hearing may be noted.
5. Concurrent otitis media should be suspected if otitis externa has been present for 2 months or longer, even if the tympanic membrane appears to be intact and no clinical signs of otitis media (drooping or inability to move ear or lip, drooling, decreased or absent palpebral reflex, exposure keratitis) are evident. Rarely, symptoms of otitis interna (head tilt, nystagmus, ataxia) may be present. Oral examination may reveal pain (severe otitis media), inflammation, or masses (especially polyps in cats)

Implications for Veterinarians/clients

• Treatment of chronic OE is costly for clients
• Cost of repetitive treatments for the client, goes beyond the monetary value of multiple office visits and numerous medications
• Emotional toll on pet owners who are unable to quickly resolve their pet’s pain and suffering
• Unresolved cases can erode pet owner confidence in their veterinarian’s abilities
• Lack of confidence can cause pet owner to seek help elsewhere
• The pet owner may switch permanently to the veterinarian who resolves or more effectively treats their pet’s Otitis externa

Keys to Managing Recurrent Otitis Externa

1. Predisposing factors increase the risk of development of otitis externa by altering the microenvironment of the ear canal allowing pathogenic or opportunistic micro-organisms to become established. Examples include ear conformation (stenosis, dense hair growth in the ear canal, excess cerumen production), lifestyle (grooming, swimming causing excessive moisture, inappropriate ear care with cotton swabs or irritant antiseptic solutions) and poor general health (pyrexia, immune suppression, and debilitation).
2. Primary factors initiate the inflammatory process within the ear canal. Most cases of otitis externa are associated with an underlying dermatologic condition. Common causes are allergic disorders (atopy, adverse food reaction) and seborrheic and glandular disorders. Foreign bodies, parasites and immune mediated diseases may also cause otitis.
3. Perpetuating factors prevent the resolution of the inflammatory process. Examples include bacterial and yeast infections and progressive pathological changes (epidermal/glandular hyperplasia causing stenosis, involvement of the middle ear).

Diagnosis

1. Based on history and clinical findings (ie. assessment of predisposing, primary, and perpetuating factors).
2. Otoscopic examination: assess degree of inflammation, ulceration, stenosis, and proliferative changes; amount and nature of debris and discharge; presence of foreign bodies, ectoparasites, and masses; and integrity of tympanic membrane.
3. Mineral oil prep (ear swab): look for otodectic and demodectic mites and ova.
4. Cytology (ear swab): look for number and type of bacteria (cocci, rods), number and type of yeasts [budding yeasts, fungal hyphae), type and activity of inflammatory cells (e.g. neutrophils phagocytizing bacteria), parasites (demodex, Otodectes cynotis), cerumen, and neoplastic cells.
5. Bacterial culture (external or middle ear exudate): indicated when bacteria (especially many rods) are found on cytology despite antibiotic therapy, or when otitis media is suspected. Note: Resistance in vitro may not correlate with clinical response (higher concentrations are achieved topically).
6. Fungal culture: indicated when dermatophytic otitis is suspected, especially in long-haired cats that have ceruminous otitis.
7. Computed tomography (CT), magnetic resonance imaging (MRI): evidence of bullous involvement (sclerosis, opacification) is seen in approximately 75% of otitis media cases.
8. Dermatohistopathology: may be indicated to identify primary cause (e.g., autoimmune disease, sebaceous adenitis, erythema multiforme), if neoplasia is suspected (ear canal mass), or if ear canal resection or ablation is performed because of end-stage otitis.
9. Additional diagnostics based on history and clinical findings include thyroid evaluation, referral for deep ear canal flushing and/or myringotomy, skin allergy testing, etc.

Dermatology Highlight

Ear cytology:
*Important for every suspected OE case
*Guides practitioner in developing treatment regimen
*Allows for complete and accurate medical record
*Easier to monitor improvement (cytologic vs clinical)
*Document white cells and quantify pathogens
# Bacteria (cocci, rods), Malassezia yeast/HPF
*Should be performed prior to submitting ear culture

Goals of cytology:
*Identify and effectively treat all secondary infections
*Formulate a diagnostic plan for identifying/controlling primary diseases

Treatment

General Principles:

1. Diagnosing and treating primary factors: Always try to make specific diagnosis of the underlying primary cause of the otitis and treat accordingly with specific therapy
2. Treat predisposing factors
3. Elimination/prevention of secondary/perpetuating factors
   • Topical anti-bacterial/anti-fungal/anti-inflammatory medications
   • Ear cleansing at home

Why Ear Cleaning is Important

Cleaning the ear canals is extremely important for the effective management of otitis externa. Accumulated cerumen, debris and exudate are irritating, prevent medications from contact with the epithelium of the ear canal, produce a favorable environment for micro-organisms to proliferate and may inactivate some antibiotics. Topical therapy should primarily focus on removing exudate, secretions and cerumen and reduce inflammation within the ear canal. This will provide comfort and relief to the patient and produce a microenvironment that no longer favors the growth of pathogenic micro-organisms.

Ear Cleaning:

1. Removes ceruminous debris allowing medication to penetrate epithelium
2. Removes purulent exudate that can interfere with antibiotics (e.g. polymyxin and aminoglycosides)
3. Removes bacterial toxins/cellular debris that can stimulate inflammation
4. Helps reduce mucopolysaccharide biofilms (impenetrable to antibiotics) produced by Pseudomonas
5. Provide antimicrobial efficacy, either by killing the organisms or detaching them from supporting surfaces
   and substrate
6. Aids in cases with failure of epithelial migration
7. Maintenance ear cleaning can reduce rate of recurrence

Difference Between Ear Cleanser vs Otic Flush

Cleanser: mechanical and chemical function to cleanse

*Should contain a surfactant solution at minimum
*A surfactant is a chemical agent that emulsifies and washes away debris/oil
*Most ear cleansers contain a ceruminolytic surfactant (ie. DSS or docusate sodium) in addition to cleansingsolution
*DSS helps to emulsify cerumen so that it can be mechanically flushed away

Flush: provides mechanical removal of debris
-Tris-EDTA flush is most commonly used; ingredients are EDTA in tris (buffered) solution and deionized water
-There is no chemical cleansing property
-Tris-EDTA flush can be formulated with antimicrobials to create a medicated flush
-Medicated tris-EDTA flush is effective in eliminating infections but will not provide ceruminolytic surfactant
properties

Highlighted Ear Cleanser

Epi-Otic® Advanced Ear Cleanser
Active ingredients:
*0.2% salicylic acid (keratoplastic, bacteriostatic, astringent)
*0.1%PCMX (anti-microbial effective against gram-negative, gram-positive, yeast)
*0.5%EDTA (anti-microbial against gram-negative organisms; potentiates PCMX)
*DSS (docusate sodium; ceruminolytic agent)
*Glycotechnology (monosaccharides only) formulated for chronic otitis (anti-inflammatory, anti-adhesive for Pseudomonas, Staphylococcus, and Malassezia)
*Anti-odor technology (aldehyde complex neutralizes odors)
*Neutral (pH 7), non-irritating

Indications:
Acute/chronic otitis
Sensitive/painful ears
Routine cleansing
356 2019 Emerald Coast Veterinary Conference

Highlighted Otic Flush

VetBioTek Ultra Otic Rinse®
Active ingredients:
*0.2% MicroSilver and lactic acid (antibacterial, antiyeast, antibiofilm)

Indications:
Non-Antibiotic ear rinse to treat and prevent acute/chronic otitis
Maintenance ear treatment

Otitis Externa Treatment Objectives:
1) Reduce inflammation » steroid (e.g. topical and/or systemic depending on severity)
2) Reduce stenosis » steroid (e.g. topical and/or systemic depending on severity)
3) Reduce mechanical occlusion » initial cleaning at time of exam
4) Treat microbial infection [according to cytology] » topical antibiotic, antibacterial, and/or antifungal

Conclusion

The keys for successful long-term treatment of otitis are:

1. Identify and control the underlying, primary disease » infectious otitis is secondary and recurrence can only be prevented if the primary disease is treated.
2. Base treatment decisions on cytology (initial and recheck) and clinical impression together.
3. Maintenance ear cleaning [e.g. 1-2 times weekly] is invaluable in preventing otitis recurrence

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References 

1. Miller WH, Griffin CE, Campbell KL (2013): Diseases of the eyelids, claws, anal sacs and ears. In: Muller and Kirk’s Small Animal Dermatology 7th Ed, St. Louis, Elsevier, 741-767.
2. Cole LK. (2004) Causes and diagnoses of otitis externa and media. Clinical Programme Proceedings of the 5th World Congress of Veterinary Dermatology, 61-68.
3. Cole LK, Kwochka KW, Kowalski JJ, Hillier A, Hoshaw-Woodward SL (2003) Evaluation of an ear cleanser for the treatment of infectious otitis externa in dogs. Veterinary Therapeutics, 4: 12-23.
4. Lloyd DH, Lamport AI, Gatto H, Rème C (2002) Potency of two ear cleansers in vitro against Staphylococcus intermedius, Pseudomonas aeruginosa and Malassezia pachydermatis. Proceedings 27th WSAVA Congress, Granada, Spain.
5. Mason CL, Steen SI, et al (2013) Study to assess in vitro antimicrobial activity of nine ear cleaners against 50 Malassezia pachydermatis isolates. Vet Dermatol. Jun;24(3):362-6
6. Angus J, Gram D, Griffin C, et al (2015) Skin and Ear Infections: Bacterial resistance & Biofilm. Roundtable Supplement to Clinician’s Brief, San Destin, FL, October.
7. Rosenkrantz W, White S, et al. (2016) Innovation for the Management of Ear Infections. Roundtable Supplement to Clinician’s Brief, February.