Otitis externa/media (Proceedings)

Otitis externa is an acute or chronic inflammation of the epithelium of the external ear canal which may also involve the pinna. It is a common disorder which may present as a primary complaint or concurrently with other problems. Occurs in 3.5% of all dogs, 10-20% of dogs presenting to DVM.

     I. Otitis externa (syndrome not diagnosis)

          A. Pathogenesis

               1. Highest incidence is between 5 to 8 years age.

               2. Long eared dogs predominate, especially Spaniels, Retrievers, and German shepherds.

               3. Feline otitis is less common.

               4. Normal cerumen is made of sebaceous and apocrine secretions. Apocrine secretions greatly increase with an otitis externa

          B. Primary Causes: Conditions that initiate the inflammatory process within the ear canal

               1. Foreign Bodies(especially foxtails in the west), primary vs. secondary

               2. Parasites: Otodectes cynotis, Demodex and other parasites.

                    a. Feline demodex may cause chronic mild ceruminous otitis with no cutaneous lesions.

                    b. Otodectes-nonburrowing mite. May cause mechanical irritation and hypersensitivity reaction. Pet with hypersensitivity will show very low numbers (<3/canal). Asymptomatic carriers may occur and require all contact animals be treated. Allergic reaction(Type III and Type I) and purulent discharge may kill mites, always check both ears.

               3. Pemphigus and other autoimmune skin diseases causing pinnal lesions with secondary otitis.

               4. Allergic diseases(especially food and inhalant allergies)

                    a. Allergic disease may present initially as unilateral disease. 40-55% of atopic disease have otitis, as much as 5% of atopics have only ear disease. Water may especially aggravate or initiate allergic otitis. Early atopic otitis has erythema of pinnae and vertiical canal while horizontal canal is WNL.

                    b. 80% of food allergic dogs have allergic otitis. Cocker spaniels may require 8 week trials.

                    c. Contact allergic reaction to otic preps may have lesions anterior to pinnae, side of face. Propylene glycol and neomycin are most common sensitizers.

               5. Extension of pinnae disorder

               6. Neoplasia-polyps, ceruminous gland carcinoma, SCC, papilloma

               7. Metabolic diseases

                    a. Hypothyroidism and sex hormone imbalance are most common endocrine disorders. Hypothyroidism must be carefully evaluated as many chronic otitis cases have sick euthyroid syndrome.

                    b. Keratinization disorders and glandular disorders affect the ear canal. Abnormal lipid production are broken down by bacteria and yeast may yield inflammatory mediators. Seborrheic otitis, Zinc and Vitamin A responsive dermatosis, Sebaceous adenitis Apocrine hypertrophy and inflammation(hidradenitis) is often present.

          C. Predisposing Causes: Facilitate the inflammation by permitting an environment conducive to survival of perpetuating factors.

               1. Conformation and moisture of the ear canal-shave medial pinnae in pendulous ears

               2. Hair in the ear canal

               3. Breed predisposition, example Shar PEI stenotic canals

               4. Immune deficiency

               5. Endocrine disorders

               6. Overtreatment of ear disorders

          D. Perpetuating Causes: Sustain and aggravate the inflammatory disease. The most common cause of recurrence. If > 4 weeks, 50% chance of tympanic membrane rupture.

               1. Occlusion of the canal-progressive pathologic changes( hyperkeratosis, hyperplasia, acanthosis, hyperpigmentation, apocrine glandular hyperplasia/adenitis, edema and fibrosis).

               2. Alteration of pH

               3. Focus of infection (otitis media)-difficult to diagnose, may have no clinical signs. Tympanic membrane thickens with chronic inflammation. Will lead to rupture or dilate into middle ear cavity. Ruptured membrane heals very quickly in dog, but may heal on itself.

               4. Medications

               5. Bacterial and Yeast infections-80% of normal ear canal have coagulase positive Staph. S. intermedius is most common pathogen from acute otitis, Pseuodmonas and Proteus are more common in chronic ear. Malasezzia sp. is primary yeast pathogen especially common with atopic disease. Yeast fermentation products have been shown to be severely inflammatory.

     II. In order to most effectively treat otitis externa, an accurate diagnosis of all underlying causes must be obtained.

     III. Diagnosis

          A. History

               1. Seasonality(allergies), age of onset

               2. Other skin diseases(seborrhea, allergies, parasites, endocrinopathies)

               3. Other animal exposure(parasites)

               4. Environmental factors(swimming, kennels, areas to which animal has been exposed-ex: foxtails in west)

               5. Unilateral vs. bilateral disease(polyps, tumors, foreign bodies)

               6. Response to previous therapies(systemic and topical).

          B. Physical examination

               1. Discharge(unilateral vs. bilateral, color, odor, texture)

               2. Concurrent nasal discharge(polyps, tumors)

               3. Aural examination(ulceration, erythema, proliferation, canal changes, calcification/stricture)

               4. Concurrent skin disease(seborrhea, allergies, parasites, endocrinopathies, autoimmune skin diseases)

               5. Ear pinnae type(pendulous vs. upright)

               6. Cranial nerve changes(head tilt, nystagmus)-however less than 10% of otitis media cases have neurologic diseases.

               7. Jaw pain and deep digital palpation(otitis media).

          C. Otoscopic examination

               1. Often need sedation or even general anesthesia to perform. Topical anesthetics may also be useful.

               2. Allows visualization of vertical and horizontal canal epithelium, tympanic membrane, foreign bodies, exudate, tumors and polyps.

               3. Excellent way to evaluate otitis media, follow feeding tube to tympanic membrane.

               4. Video-Otoscopy is preferred way to evaluate the ear canal and middle ear.

          D. Cytology

               1. Cotton-tipped applicator used to collect material which is placed on microscope slide.

               2. Use Diff-Quik to stain heat fixed specimen. Observe on dry objectives, oil not necessary. Evaluate number of epithelial cells, Malassezia numbers, bacteria(rods vs. cocci, intracellular vs. extracellular).

          E. Cultures

               1. Bacterial culture and sensitivity(MIC are more helpful for topicals), DTM culture of pinnae.

               2. Normal flora consists of Coagulase (+) Staphylococcus, Malassezia pachydermitis.

               3. Proteus, Pseudomonas, Streptococcus. and E. coli seen in diseased ears.

               4. Remember that sensitivities are based on systemic administration of antibiotics, not topical administration.

               5. Should tympanum be ruptured for culture??

          F. Histopathology-may be performed if tumor or polyp is suspected, can also biopsy horizontal canal.

          G. Radiology-little value in otitis externa. May be useful in evaluating tympanic bullae in cases of otitis media(at least 25% of false negatives). CT Scan much more accurate.

     IV. Clinical Management

          A. Treat underlying causes and treat for appropriate time period, have numerous rechecks.

          B. Ear Flushing-many medications available which are ceruminolytic. Ceruminolytic agents break down lipids(waxy or ceruminous otitis) through detergent or surfactant actions. Less greasy otitis may be treated with humectants to moisturize. Foaming actions work best with purulent exudative otitis. ClearX cleanser(DVM) is especially helpful to remove exudate but must be rinsed thoroughly.

               1. Must use surgical head otoscope-Focuscope has excellent system for examination of canal, powerful illumination and heads that do not easily detach during flushing. (MDS Inc., P.O. Box 1441, Brandon, FL 33511; 813-653-1180)

               2. Should use concurrent suction apparatus is often very helpful.

               3. Ear curettes, alligator forceps, biopsy forceps also helpful.

               4. Evaluate tympanic membrane after cleansing.

               5. Video-Otoscopy:Vastly improved way to examine the ear canal. Magnification allows easier fewing of lesions and can document via color photos or saving to CD/Memory card. Can flush and evaluate middle ear. Karl Storz (800) 955-7832 and MedRx (888) 392-1234 are excellent units.

          C. Active ingredients commonly used in otic preparations

               1. Ceruminolytic: Hexamethyletetracosane, DSS, Squalene

               2. Keratolytic: Carbamide peroxide(releases O2 and urea which is hygroscopic), Benzoic acid, Salicylic acid, Sulfur, Resorcinol

               3. Antifungal: Nystatin, Thiabendazole, Miconazole, Clotrimazole, Cuprimyxin

               4. Antibacterial: Chloramphenicol, Colitin, Neomycin B sulfate, Gentamycin, Polymixin B, Penicillin G, Bacitracin, Sulfacetamide, Sulfur, Enrofloxacin

               5. Glucocorticoids: Hydrocortisone, Prednisolone, Isoflupredone acetate, Triamcinolone acetate, Dexamethasone, Flucinolone acetonide

               6. DMSO

               7. Antiparasitics: Pyrethrins, Thiabendazole, Carbaryl, Rotenone

               8. Topical anesthetics: Tetracaine, Lidocaine

               9. Drying agents: Alpha-hydroxy acids, Alcohol

          D. Apply specific medication to entire canal after cleansing. Should be at least ½ ml.

          E. Systemic medications may be beneficial in some cases

               1. Antibiotic based on bacterial culture and sensitivity results(remember aminoglycoside ototoxicity), especially helpful in cases of otitis media.

               2. Glucocorticoids may be helpful in cases of proliferative otitis or to reduce edema of canal. Prednisone (0.25-0.5 mg/lb.) daily for 7-10 days, then every other day for 1-2 weeks.

               3. Ivermectin(200-300 ug/kg) or Selemectin in cases of recalcitrant Otodectes.

          F. Topical Medications-must use good cleanser(Epi-Otic, Oticalm, Chlorhexidene flushes, Oticlens) prior to medicating. Make sure owner knows how to apply ear medications.

               1. Topical use of injectable LA Baytri(100mg/ml)l-unapproved by USDA for otic, usually mixed into Tris EDTA

               2. Tris EDTA as a topical premedication helps increase Pseudomonas susceptibility to topical antibiotics(aminoglycosides).

               3. Gentocin otic contains betamethasone valerate; do not use powerful topical steroid with ulceration, adrenal suppression can occur with long term use.

               4. Liquichlor has chloraphenicol as the antibiotic, have owners wear gloves when applying.

               5. Zymox® is unique Triple enzyme system that is useful in cleaning and treating low grade yeast infection. It comes with/without 1% hydrocortisone and excellent for long term management of allergic ears.

               6. Tresaderm; often used in mixed infections, effective against Otodectes infestation.

               7. Miconazole or Clotrimizole; effective against tough Malassezia infections.

               8. Synotic; effective for allergic otitis and ceruminous otitis without significant bacterial or yeast otitis

               9. Otomax and Mometomax-poly pharmacy, effective against Gram negatives and Malassezia with potent topical steroids. Adrenal suppression can occur with long term use.