Lecture 2 - Diseases
of the Ear
Lecture 2 - Diseases of the Ear
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).
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. Â Â Continuare cursului nr. 2 aici .
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