Proliferative changes within canals stenosis and folding of canal lumen inhibits effective cleaning and application of topical therapy and traps secretions, debris and microbial metabolic by-products further pathologic changes.
Hyperkeratosis of stratum corneum increased secretion and epithelial debris in canal proliferation of bacteria and yeast.
Edema.
Apocrine gland hypertrophy, hyperplasia or inflammation.
Dry coffee grounds - Otodectes- however these are not sensitive distinguishing signs.
Pruritus or pain.
Pinnal lesions (erythema, swelling, scaling, crusting, alopecia).
Chronic otitis externa
Yellowish/brownish ceruminous otic exudate .
Hyperplasia of ear canal .
Thicker, firmer, less pliable vertical and horizontal canal.
Aural hematomas.
Acute moist dermatitis face.
Pruritus and skin lesions in other body locations.
Systemic signs.
Diagnostic investigation
Otoscopic examination
Exudate .
Erythema .
Proliferative changes .
Foreign body identification .
Ulceration .
Ruptured tympanic membrane .
Otodectes cynotis mites .
Microscopy
Diff-Quik or gram-stained smears of ear swab.
Cocci :
Staphylococcus intermedius.
Streptococcusspp.
Rods :
Pseudomonasspp .
Proteusspp .
Escherichia coli.
Klebsiellaspp.
Bacterial infection.
Phagocytosis of bacteria.
Toxic neutrophils.
Yeast infection.
Malassezia pachydermatis: 5-10/high power field significant.
Candidaspp:
Acantholytic epidermal cells - suggestive of pemphigus complex.
Otodectes cynotis mites or eggs.
Bacteriology
Culture should be taken from both the external (horizontal) canal and middle ear in cases of otitis media because different bacteria may be present in various parts of the canal.
Culture and sensitivity if microscopy demonstrates rods or white blood cells in discharge or chronic otitis externa.
Other
Skin scrape for parasites, eg Sarcoptes , Demodex , dermatophytes.
Intradermal skin test for atopy . Topical glucocorticoids in otic medications may interfere with this
Elimination dietary trial for food allergy .
Biochemistry
To rule out underlying endocrinopathies.
To rule out systemic disease.
Histopathology
Biopsy of ear canal:
Neoplasia, polyps.
Keratinization disorders.
Auto-immune diseases.
Radiography
Skull radiographs for diagnosis of otitis media .
In some chronic cases calcification of the ear canal may be seen on radiography .
Confirmation of diagnosis Discriminatory diagnostic features
Ear canal cleansing with ceruminolytics (contraindicated if ruptured tympanic membrane) using ear bulb syringe or syringe and feeding tube.
Dry ear canal with drying agent (contraindicated if severely inflammed or ulcerated).
Topical antibacterials
Topical Polymixin B is highly effective against Pseudomonas, as long as exudate is not present.
Baytril otic , contains enrofloxacin and silver sulfadiazine (licensed for use in dogs in US only).
See ear therapeutics .
If bacteria and white blood cells identified by cytology.
Topical glucocorticoids
See ear therapeutics.
If significant inflammatory component, eg pruritus, swelling, proliferative changes or glandular secretion. Use least potent formulation which will be effective as percutaneous absorption shown to occur leading to iatrogenic hyperadrenocorticism.
Topical antifungals
See ear therapeutics .
If yeast identified by cytology in significant numbers (5-10/high power field or >10 if numerous bacteria and <5 if only yeast).
Topical ectoparasiticides
See ear therapeutics .
If parasites seen on otoscopic or microscopic examination.
Standard treatment
Systemic antibacterialsif :
Fluroquinolones are usually used against Pseudomonas. For resistant cases Ticarcillin can be tried (antibiotics should be given for 6-8 weeks).
Otitis media.
Severe otitis externa, eg Pseudomonasinfection.
Chronic otitis externa where proliferative changes inhibit use of topical therapy.
Acute otitis externa where pain inhibits use of topical therapy.
Short course of systemic glucocorticoids if :
Marked inflammation or proliferative changes.
Chronic otitis externa where proliferative changes inhibit use of topical therapy.
Allergic cause underlying severe otitis externa.
Systemic antifungals if :
Malasseziaotitis media.
Severe recurrent Malasseziaotitis externa.
Surgery
Lateral wall resection .
Vertical canal ablation .
Total ear canal ablation :
Stenosis of canal.
Tumors or polyps.
Chronic recurrent otitis externa despite full diagnostic work-up and appropriate treatment.
Monitoring
Worsening of symptoms: change medication (?irritant or contact hypersensitivity).
Blood samples to monitor side-effects if long-term systemic or topical glucocorticoids used.
ACTH test .
Subsequent management
Treatment
Maintenance ear cleaning every 3-7 days +/- topical therapy.
Topical low potency steroid if ceruminous glands continue to over-produce exudate, eg hydrocortisone-containing solution, +/- topical antibacterials and/or antifungals if secondary infection.
Monitoring
Subsequent history, clinical and otoscopic findings and cytology.
Martin B J L, Lupiola G P, Gonzalez L Z & Tejedor J M T (2000) Antibacterial susceptibility patterns of Pseudomonas strains isolated from chronic canine otitis externa.J Vet Med B Infect Dis Vet Public Health47 (3), 191-196.
Cole L K, Kwochka K W, Kowalski J J & Hillier A (1998) Microbial flora and antimicrobial susceptibilty patterns of isolated pathogens from the horizontal ear canal and middle ear in dogs with otitis media.JAVMA212 (4), 534-538.
Nuttall T J (1998) Use of ticarcillin in the management of canine otitis externa complicated by Pseudomonas aerginosa.JSAP39 (4), 165-168.
Mansfield P D et al(1990) Infectivity of Malasezia pachydermatis in the external ear canal of dogs.JAAHA26 , 97-100.
August J R (1988) Otitis externa in the dog and cat. Part II - Pathogenesis of the Disease.Western Veterinary Conference, Las Vegas, 162.
Moriello K A et al(1988) Adrenocortical suppression associated with topical otic administration of glucocorticoids in dogs.J AVMA193 , 329.
August J R (1986) Evaluations of the patient with otitis externa.Dermatology Reports5 , 1.
Woody B J & Fox S M (1986) Otitis externa - seeing past the signs to discover the underlying cause.Vet Med Small Anim Clin87 , 616.
Wilson J F (1985) A practitioner's approach to complete ear care.Dermatology Reports4 , 1.
Dickson D B & Love D N (1983) Bacteriology of the horizontal ear canal of dogs.JSAP24 , 413.
Griffin C E (1981) Otitis externa.Comp Cont Ed Prac Vet3 , 741.
Other sources of information
Morielo K A & Mason I S (1995) Handbook of Small Animal Dermatology. Pergamon Press. pp 259-267 (Concise for quick reference).
Muller G H et al(1995) Muller and Kirk's Small Animal Dermatology. 5th edn. Philadelphia: W B Saunders. pp 970-987 (Detailed dermatology text book for in-depth reading).
Merchant S & Griffin C (1994) The 1994 Ear Care Symposium, Otitis Externa, the 21 Most Commonly Asked Questions. Veterinary Learning Systems Co Inc. (Practical advice on treatment).
McKeever P J (1993) In: Manual of Small Animal Dermatology. P H Locke, R G Harvey & I S Mason (eds). Cheltenham: BSAVA. pp 131-140 (Concise for quick reference).
Griffin C E, Kwochka K W & MacDonald J M ( 1993) Current Veterinary Dermatology - The Science and Art of Therapy. St Louis: Mosby Year Book. pp 245-262 (Well presented dermatology text book with good treatment plans).
Vetstream contributor(s)
Dr Karen Campbell DVM MS DipACVIM DipACVD , University of Illinois, Veterinary Medical Teaching Hospital, 1008 West Hazelwood Drive, Urbana, IL 61802, USA.
Dr Rosanna Marsella DVM DACVD , PO BOX 100126, SACS, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126, USA.
David H Scarff BVetMed CertSAD MRCVS, Anglian Referrals, 2 Highlands, Old Costessey, Norwich NR8 5EA, UK. Tel/Fax: +44 (0)1603 743415.
acute otitis externa +/- perpetuating factor 
Topical glucocorticoids in otic medications may interfere with this
Use least potent formulation which will be effective as percutaneous absorption shown to occur leading to iatrogenic hyperadrenocorticism.