Lecture 2 - Diseases of the Ear

Lecture 2 - Diseases of the Ear
Lecture 2 - Diseases of the Ear
I. Anatomy of the ear
A. Outer ear
1.The ear canal consists of the vertical and horizontal canals. The horizontal canal terminates at the tympanic membrane (TM) which consists of the dorsal pars flaccida (opaque, pinkish to white in color with superficial vessels) and the ventral pars tensa (semi-transparent, glistening). The malleus (auditory ossicle) can often be seen beneath the pars tensa.
2.The epidermis lining the ear canal contains hair follicles, sebaceous glands and modified apocrine (ceruminous) glands that contribute to ear wax (cerumen) production. Beneath the dermis and subcutis is the rolled cartilage (auricular, annular) which supports the external ear canal.
B. Middle ear
1.The middle ear includes the tympanic membrane, tympanic cavity, tympanic bulla, auditory ossicles (malleus, incus, and stapes), and auditory (eustachian) tube which connects the tympanic cavity to nasopharynx.
2.The facial nerve along with branches of the sympathetic and parasympathetic nerves course near the middle ear.
3.Function: air vibrations strike the TM and are transmitted to inner ear by auditory ossicles. Stimulation of auditory receptors in inner ear results in the perception of sound.
C. Inner ear (cochlea, vestibule, semi-circular canals): function in hearing and balance.

From: Current Veterinary Dermatology: Griffin, Kwochka, MacDonald Mosby 1993
Otitis Externa
II. General considerations
A. Incidence: otitis externa is common
Otitis externa occurs in about 15 - 20% of canine and 4 - 7% of feline cases presented. The lower incidence in the cat is likely due to anatomical factors (more erect ear, less hair, and shorter vertical canal).
B. Pathophysiology
1.Chronic inflammation results in hyperplasia of epidermis and apocrine glands, dermal edema, and fibrosis. These changes cause swelling and stenosis of the ear canal.
2.Long-standing chronic irritation can result in mineralization and subsequent ossification of the annular and auricular cartilages (rock hard on palpation).
III. Etiology
A. Multifactorial disease process: predisposing, primary and perpetuating factors
Predisposing factors change the microclimate in the ear and increase the risk of disease, primary factors directly induce disease, and perpetuating factors tend to complicate otitis and prevent resolution.
1.Predisposing factors: conformation of ear (droopy ears, etc.), excessive moisture or hair in ear, treatment with irritating topical agents, tumors, polyps, and underlying systemic disease.
2.Primary causes: parasites, dermatophytes, atopy, food allergy, contact allergy, primary seborrhea, autoimmune disease, foreign bodies, glandular hyperplasia,
3.Perpetuating factors: underlying otitis media, ear pathology (hyperplasia, edema, fibrosis), bacteria, and yeast.
B. What's most common?
1.Cats frequently suffer otitis externa due to Otodectes cynotis and dogs often due to underlying atopy, food allergy, or keratinization disorders.
2.Obtain a good history, examine the animal carefully and perform basic diagnostic tests to identify likely predisposing, primary, and perpetuating factors.
IV. Diagnosis
A. History
Head shaking, aural pruritis, otic discharge, and malodor are common. Aural hematomas may occasionally develop secondary to self-trauma/head shaking.
B. Physical exam
1.General exam: look for underlying diseases that predispose to otitis
*Q: What clues on physical exam are suggestive of underlying atopy? Food allergy? Hypothyroidism? Keratinization defects? Demodex?
2.Appearance of otic discharge: may provide clues
A "coffee-grounds" appearance is suggestive of ear mites, a moist brown exudate suggests yeast or Staph, oil yellow to tan discharge suggests ceruminous otitis, and a purulent cream-yellow discharge suggests gram negative bacteria.
C. Examination of the ear
1.Appearance of ear canal
a.The normal ear canal is pale to light pink in color and slightly moist with cerumen. Some animals may have hairs in the vertical ear canal.
b.The ear canal becomes erythematous, swollen, and narrowed with acute otitis. As inflammation continues, increased sebaceous gland secretions, hyperplasia of the epidermis, and dermal edema occur. Edema causes constriction of the canal lumen and pain from entrapment of nerves against the cartilage.
c.With chronicity, proliferation of connective tissue in the dermis and subcutis gives rise to fibrosis and additional thickening of skin. Further occlusion of the ear canal occurs ("cauliflower ear") and ossification of auditory cartilage may occur.
2.Otoscopic exam
a.Use aseptic cones soaked in cold sterile solution (rinse prior to use). Examination of the inflamed ear is uncomfortable and painful - don't hesitate to use adequate sedation or general anesthesia. It may be necessary to treat firstto help alleviate swelling and pain and facilitate adequate otoscopic exam.
b.Tympanic membrane (TM): may be difficult to visualize (one study showed that a satisfactory view of the tympanic membrane in patients with chronic otitis was only obtained in 28% of patients). Chronic otitis externa inevitably gives rise to otitis media (see later).
D. Diagnostic evaluation
1.Samples of otic discharge
Obtain specimens from horizontal ear canal (place Q-tip through guarded lumen of otoscope cone). Harvest samples from both ears.
a.Cytology: roll a small amount of discharge on glass slide, heat fix, and stain (Diff-Quik). Evaluate for microorganisms (bacteria, yeast) and inflammatory cells. *Q: Do dogs normally have microorganisms in their ears? Yes, small numbers of yeast (Malassezia pachydermatis) and gram positive cocci (Staph, Strep) are normal.
b.Oil smear: place small amount otic discharge on a slide and mix with oil to look for Otodectes cynotis.
2.Pursue additional diagnostic tests as indicated
a.Unless underlying causes of otitis externa are addressed, treatment will only temporarily ameliorate clinical signs.
b.Perform allergy testing, skin scrapings, DTM culture, endocrine testing, etc. as indicated
i.Hypersensitivity (allergic) disease: is the most common cause of persistent bilateral otitis externa in the dog. Up to 55% of dogs with atopic dermatitis and 80% of dogs with food allergy have concurrent otitis externa (and some will have just unilateral signs). Otitis externa (pruritis or erythema of the ears) may be the ONLY sign in 5% of atopic dogs and 25% of food allergic dogs.
ii.Keratinization defects and endocrinopathies: may see chronic ceruminous otitis externa.
3.Other diagnostic tests
Culture/sensitivity is indicated in cases of chronic otitis externa and otitis media/interna to help guide systemic antibiotic therapy (see later).
V. Treatment
A. General guidelines
1.Clean the ears first - topical medications are often ineffective in the face of inflammatory exudate.
2.Sedation or general anesthesia is frequently required for exam and treatment of an inflamed and painful ear. Treatment prior (with glucocorticoids) helps alleviate inflammation and allows for a more effective otoscopic exam.
3.If the integrity of the tympanic membrane is compromised, ruptured, or unknown DO NOT use potentially ototoxic cleansing solutions or medications.
B. Glucocorticoids (GC's) (see table)
1.Systemic GC's (prednisone, prednisolone)
Indicated if inflammation, swelling, and stenosis of the ear canal are present. Treatment helps to "open" the ear canal and allow for more effective topical therapy. Dose: anti-inflammatory dose of oral prednisolone (0.5 - 1.5 mg/kg/day in the dog and 1 - 3 mg/kg/day in the cat) for 3 to 5 days.
2.Topical glucocorticoids: beneficial in most
Decreases inflammation, pain, swelling, pruritis, exudation, and proliferative changes thus facilitating drainage and ventilation. Most topical otic preparations contain steroids (see table).
C. Cleaning the ear
1.Remove excess hair. *Q: How would you do this?
Clippers can be used to gently remove excess hair at entrance to external ear canal. Plucking hair from the vertical ear canal should only be performed if hairs are thought to be directly contributory to otitis.
2.Cleansing solutions (see table)
a.Ceruminolytics: emulsify waxes and lipids so they can be flushed from ear - helpful if excessive waxy secretions are present. Some products are ototoxic (do not use with compromised TM).
b.Cleansing agents: mechanically flush away otic debris. Some have antibacterial activity, anti-yeast activity, or drying effects. Many (such as chlorhexidine) are potentially ototoxic. Solutions safe to use in face of ruptured eardrum include sterile lukewarm 0.9% saline, DermaPet Ear/Skin Cleanser, and acetic acid preparation (white vinegar diluted 1:1 with water).
c.Technique: BE VERY GENTLE as the TM is easily injured. *Q: What complications may result from poor technique? A: Ruptured eardrum, vestibular signs, Horner's and hearing loss.
i.In awake animal, fill ear canal with cleansing solution, massage thoroughly, allow animal to shake head, and gently wipe away dislodged debris.
ii.Anesthetized animal: gently infuse cleansing agent, massage ear canal, and then suction using red rubber catheter attached to 12 ml syringe while observing through otoscope cone. An ear loop is helpful for removing debris lodged near TM. The MedRx Video Vetscope allows for magnified exam, flushing, and suctioning under direct visualization.
iii.At home: have owners fill ear canal completely, massage base of ears, let animal shake, and then wipe away loosened debris. Clean ears once daily for 7 to 10 days; follow with once to twice weekly maintenance cleaning. Monitor response to therapy with recheck exam and cytology.
d.Drying agents: helpful in dogs susceptible to moist ears (swimmers, etc.). Apply weekly to help facilitate evaporation.
VI. Therapeutics for specific diseases (see table)
A. Bacterial otitis
1.Common pathogens include Staph intermedius (most common), Pseudomonas aeruginosa, Proteus mirabilis, E. coli, Corynebacterium, and Streptococcus spp. Multiple organisms are often present in cases of chronic otitis.
2.Cleansers: purulent discharge will inactivate many antibiotics, so ears must be clean for effective therapy. Chlorhexidine, dilute povidone-iodine, or acetic acid based flushes work well.
3.Topical antibiotics: products containing neomycin and polymxyin B, are usually effective in uncomplicated cases while antibiotics with extended spectrum (fluroquinolones, aminoglycosides) are used for more severe or resistant cases. See otitis media (below) as well as table for listed antibiotics.
4.TrisEDTA: helpful in treatment of gram negative infections (such as Psuedomonas). Promotes an alkaline pH (8.0) and facilitates increased antibiotic efficacy.
5.Systemic antibiotics: indicated in cases of suppurative or chronic otitis, or otitis media (see below).
B. Yeast otitis: usually due to Malassezia pachydermatis
1.Cleansers: acetic acid based solutions (DermaPet Ear/Skin Cleanser or white vinegar/water) may effectively address yeast overgrowth.
2.Topical anti-yeast preparations: include 2% miconazole, clotrimazole, and Tresaderm (containing thiabendazole). Baytril Otic (containing the antifungal ingredient silver sulfadiazine) may also be used. Thiabendazole and silver sulfadiazine are purportedly less efficacious.
3.Systemic agents: indicated in chronic refractory otitis externa or otitis media (see later).

Malassezia pachydermatis
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Otodectes cynatis
Diagrams from: Muller & Kirk's 5th edition.
C. Otodectes cynotis: ear mites
1.Overview
Ear mites are a common cause of otitis externa (50% of cases seen in the cat and 5 - 10% of cases in the dog). Mites feed on lymph and epidermal debris, inject mite antigen and induce host hypersensitivity reaction. As few as 2 - 3 mites can cause severe clinical signs. Mites may migrate to other areas of the haircoat (important to treat entire body) and are highly contagious (treat all in-contact dogs and cats). Treatment should continue for 4 weeks (to insure complete therapy as not all products are effective against incubating mite eggs).
2.*Topical otic preparations
Topical preparations include: Tresaderm (active ingredient - Thiabendazole), Acarexx (active ingredient ivermectin), Milbemite (active ingredient milbemycin) (latter two are licensed for use in cats), Cerumite (active ingredient pyrethins), and Revolution (active ingredient selamectin). *Consult package inserts for dosing instructions.
3.Topical body treatments
a.Revolution: treatment of choice. Safe, effective and labeled for treatment of ear mites. Dosing regimen (labeled instructions): apply once monthly for two treatments.
b.Systemic ivermectin: alternative therapy, not a first-line treatment
This drug is not labeled for this use. MUST test for heartworm disease first, do NOT use in Collie breed or any crosses thereof, and avoid use in animals < 4 months of age. Dosing regimen: 250 ug/kg SQ: repeat every 10 - 14 days for 2 to 3 treatments.
D. Ticks
1.Otobius megnini: spinous ear tick
Found in the southwest United States. Parasitic larvae and nymphs feed within ear causing a significant inflammatory reaction in the ear canal. Treatment = removal of ticks, tick control measures (see later) and management of secondary otic inflammation.
2.Other ticks (Dermacentor, Rhipicephalus sanguineus, etc): may also infest ear canal.
Treatment involves symptomatic ear care, removal of ticks and control of ticks on the body as well as in environment. Potential treatment options include Preventic collar, Amitraz dips, Frontline, Advantix, and Revolution (*consult package inserts for dosing instructions).
E. Other
1.Foreign bodies: remove and provide symptomatic ear care
Heavy sedation to general anesthesia may be necessary for removal. Alligator forceps can be advanced through otoscope cone to aid in retrieval of foreign bodies (such as grass awns).
2.Neoplasia: typically unilateral
a.Benign: nasopharyngeal polyps (cats). Usually arise from the mucosal lining of the middle ear, Eustachian tube, or pharynx. Nasopharyngeal polyps tend to extend through TM (causing signs of otitis) or into nasopharynx (causing respiratory signs). Etiology unknown, and most successfully managed via complete surgical excision (consult reference source).
b.Malignant: ceruminous gland adenocarcinoma, squamous cell carcinoma, other.
Ceruminous gland tumors are the most common ear canal tumor in both the dog and cat.
Otitis Media/Interna
A. Etiology
1.Otitis externa
Otitis media usually results from chronic (> 45 - 60 days) otitis externa (infection spreads across the tympanic membrane). Otitis media is present in > 50% of dogs with chronic otitis externa.
2.Ascension via eustachian tube
In the cat, otitis media may also result from upper respiratory tract disease, invasion of nasopharyngeal polyp across TM, or damage to the TM from ear mites.
3.Microbes
Staph intermedius and Psuedomonas aeruginosa (as well as Strep, Proteus, Klebsiella and E.coli). are common isolates in the dog. Staph intermedius, Strep and Mycoplasma have been isolated in cats (as well as Psuedomonas and others). Yeast otitis media is usually due to Malassezia pachydermatis.
B. Clinical signs
1.As for chronic otitis externa (otitis media is a major cause of recurrent otitis externa).
2.Tympanic membrane: may be normal or abnormal
a.The TM may appear discolored, bulging, ruptured, absent, or normal. In one study, 70% of eardrums in dogs with documented otitis media were intact (eardrum can seal with infection trapped inside bullae).
b.Mucoid exudate in bulla or horizontal ear canal: produced by lining of tympanic bulla and may be noted in horizontal ear canal when it leaks through ruptured TM.
3.Cranial nerve signs: may note Horner's (damage to sympathetic supply), facial nerve palsy (damage to facial nerve), or KCS (damage to parasympathetic nerve supply to lacrimal gland).