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derm
11/16

A practical approach to otitis externa

otitis 
externa: inflammation of the outer ear; can lead to otitis media or 
interna.
[re: handout - first several pages give background info in 
outline form - detail is in small animal derm textbook. back of handout 
has info from an article published in 1997 outlining all the meds out 
there for ears.]

etiology:
there are three categories 
1. predisposing 
factors: things that make a particular dog more prone to otitis externa, 
be it from genetics or environmental factors. things like ear anatomy, 
things the owner does, things the dog does like swimming
2. primary 
causes: things that cause infection to keep coming back, things you need 
to find and remove. if you get rid of it maybe it won't come back. 
allergies, hormonal disorders, etc.
3. perpetuating factors: things that 
bring the dog back - bacteria, yeast, fungi, that cause the problem.


when dealing with recurrent otitis you really want to dx primary cause: 
does dog have bilateral problem? if yes, is dog pruritic? if yes, look at 
hypersensitivities - food allergy, atopy, flea allergy - do food trials, 
intradermal testing, and flea comb.  if not pruritic, but is bilateral, 
look at hormonal imbalances, systemic dz - do cbc/chem, fT4/TSH, ACTH.
if 
not bilateral, do an otoscopic exam and maybe bulla rads to look at 
middle ear. when you have unilateral problem it's more likely to be 
tumor, foreign body, or middle ear disease. 

otoscopy: simple to do in 
the office, as long as the dog cooperates. can see if tympanic membrane 
is intact or ruptured, can see tumors. some dogs aren't cooperative. in 
our hospital we have a video otoscope - like endoscope with special oto 
attachment. gives a better 3D picture. can see more stuff, can pass 
biopsy instrument through a port to remove FB or biopsy a tumor. 

bulla 
rads:
mineralizing otitis can be seen - this is a consequence of chronic 
otitis with fibrosis, which becomes mineralized. in the area of the ear 
canals you see bone density fragments. 

hypersensitivity diseases - a 
very common primary cause.
-atopy: the 2nd most common - otitis externa 
may be the only clinical sign, in about 3% of the cases. 
-food 
hypersensitivity: 3rd most common - 80% of food allergic dogs have 
otitis, some present only with otitis
-contact hypersensitivity: less 
common - usually contact reaction to neomycin or propylene glycol in ear 
meds
-cutaneous drug reaction - least common - systemic reaction usually 
accompanied by erythema multiforme. ears aren't the only problem.


[slides]

scaling and erosion of epidermis - cutaneous drug eruption, rxn 
to neomycin

Keratinization disorders: 
primary idiopathic seborrhea - 
common in cocker spaniels, dx by biopsy. ears are not the only affected 
area. 
hypothyroidism - affects metabolism of all systems including 
glandular secretions and keratinization. 
sex hormone imbalances - rare, 
but seen. bx alopecic skin.

glandular disorders:
ceruminous gland 
hyperplasia - see w/otoscope
sebaceous gland hyper/hypoplasia
altered 
secretion
altered types of secretions

autoimmune:
pemphigus foliaceous 
or erythematosis
lupus
cold agglutinin dz
distemper virus

why use an 
otoscope?

-foreign body may be present even if bilateral dz
-tumors and 
polyps
-ruptured tympanic membrane
-anatomic abnormalities (stenosis, 
torturous canal?)
-assist in ear flushing esp if under anesth using video 
otoscope

grass awn plucked from ear - slide
cystic apocrine glands with 
otodectes - looks like grapes or swollen ticks in there! this is the 
glands becoming cystic secondary to the mites.
papillomas - another ear 
tumor- less common

anatomic abnormalities: stenotic ear canals in shar 
pei, excessive hair in canal in cocker spaniels, pendulous pinnae as in 
bassett hound; tortuous ear canals

changes seen with chronicity:

hyperkeratosis, hyperplasia of glands and epidermis, edema - these all 
complicate things by reducing air circulation. 
apocrine gland 
hypertrophy/hyperplasia
hidradenitis - increased apocrine secretion

fibrosis
mineralization

sebaceous glands displaced by apocrine glands 
--> apocrine glands hypertrophy, dilate, then eventually the cystic 
glands rupture --> big inflamamtory response with histiocytes, mast 
cells, PMNs, giant cells, fibroblasts -->dermal fibroplasia and 
ossification occurs at which point usually surgery is only option. 


slide: dog 2 yrs post Zepp procedure who developed stenotic 
mineralization.
study showed that most cocker spaniels who had zepp 
procedures did go on to need total ear ablations despite having the Zepp. 
so, realize if you do not take care of the primary cause, these surgeries 
won't really help that much - some dogs have total ear ablations and 
still have "pinnitis" 

perpetuating factors must be diagnosed and 
treated also - but again, also want to find primary cause!! anyway, to dx 
perpetuating factor - 
ear mites - coffee grounds d/c

mineral oil prep - 
swab out some d/c put on slide with oil and look at it --> might see 
demodex, but usually there will be other affected sites --> tx mitaban, 
ivermectin.

might see otodectes - most common ear mite - tx 
thiabendazole, ivermectin, carbaryl, pyrethrins, rotenone. it is 
contagious so have to tx other animals in the house. 

might see 
sarcoptes though this would be rare. tx lime sulfur, ivermectin - whole 
body. also tx contact animals. 

another diagnostic method is cytology - 
take swab, insert deep into ear canal, swab directly onto slide, stain 
with diffquick

may see cocci: s. intermedius, strep spp -- tx 
gentomicin, neomycin - topically should be safe but do not apply if 
ruptured eardrum present.

may see malassezia: very common, very 
pruritic. tx miconazole, clotrimazole, nystatin, thiabendazole. these are 
very easy to get. miconazole is least likely to encounter resistance. 

may see rods: pseudomonas, proteus, e.coli, enterobacter - pseudomonas 
often highly resistant...when you see rods, do a c & s - you want to make 
sure bacteria are susceptible to your antibiotic. 

pseudomonas otitis is 
very inflammatory, with erosions, ulcers, purulent foul d/c 

malassezia 
- peanut shaped organism

treatments: 

ceruminolytic agents - it's 
important to clean the ear b/c putting meds in a dirty ear won't help . 
but you want to avoid causing more trauma, too.

ClearX ear cleansing 
solution (DVM) - DSS, Urea peroxide
(DSS is a good ceruminolytic, urea 
peroxide is another)

Cerumen (Evsco) - squalene - a study was done to 
see which ceruminolytic was best to use in dogs with ruptured tympani - 
this is the only one that didn't cause significant trauma to the middle 
ear. this stuff feels really oily and greasy. 

Murine Ear drops - 
carbamide peroxide
Adams Pan-otic - DSS

cleansing agents:

Nolvasan otic 
- chlorhexidine - not good with ruptured eardrum. antibacterial
Oti-Clens 
(Pfizer) - malic, benzoic, salicylic acid - pretty safe, could be 
irritating and sting in ulcerated ear. does have antifungal activity

solvaprep - surfactants
Epi-Otic (virbac) - lactic, salicylic acids

Chlorhexiderm flush
Corium 20 - SDA-40B
GentLClnes - lactic, salicylic 
acids...

ear flushing equipment: flush bowl, tomcat catheters, red 
rubber catheters, ear bulb syringe. 

topical meds:
-preferred method of 
tx for otitis externa
-tx 14-21 days depending on severity of infxn. some 
meds labelled like otomax for 7 days, but you should use 14-21 days.

-look at vehicle ingredient is in - for dry, scaly ears use an ointment 
or oily vehicle; for moist, exudative ears use a solution or lotion. 


panalog, otomax, tresaderm, gentocin otic, etc. many things.
otomax has 
an antiinflammatory, antibiotic, and antifungal. not all dogs need all 
that stuff though. if you have a yeast infection, just use conofite with 
miconazole in it. 
liquichlor - not recommended - very oily, contains 
cerumene and chloramphenicol. probably still on the market simply because 
it was grandfathered in. 
panalog pretty cheap - antifungal, 
antibacterial, antipruritic. 
tresaderm - has thiabendazole in it which 
can kill malassezia and otodectes. warn owners it contains dexamethasone 
which is very potent - if owner gets it on hand and wipes face, it could 
cause some scarring on the face. 

topical meds:
antibiotics:

aminoglycosides most common - gentamicin, neomycin, amikacin, polymyxin B 
- these are associated with ototoxicity, though rarely seen. these can 
all be inactivated by pus, too.
enrofloxicin - can make this yourself 
using injectable prep
timentin - as above
silver sulfadiazine 1% - as 
above using powder
chloramphenicol - avoid

antiparasitics: 
thiabendazole, pyrethrins, carbaryl, rotenone
antifungals: miconazole, 
nystatin, thiabendazole, acetic acid, chlorhexidine 4%

glucocorticoids 
useful in hyperplastic canals - triamcinolone, betamethasone, 
dexamethasone, hydrocortisone (least potent, so best choice for longterm 
use - BurOtic HC good for allergic otitis not complicated by microbes)


systemic therapy:
indications: severe otitis externa, otitis media, 
marked proliferative changes, inability to administer topicals.

systemic 
meds alone aren't likely to cure otitis externa, but make a good adjunct 
to topical therapy. 

systemic meds:

antibiotics - always choose based 
on culture and sensitivity, esp if treating otitis media. 
antifungals - 
ketoconazole is the drug of choice for yeast otitis media. this won't 
really help yeast otitis externa though.  
antiparasitic - ivermectin, 
offlabel
glucocorticoids - may be necessary with marked inflammation and 
stenosis of ear canal. short course 5-10 days may be enough to open canal 
so topical meds can get in there.

other conditions affecting the ear:


these are relatively uncommon.

solar dermatitis - common in lightly 
pigmented animals in sunny climate
frostbite - in the north - affects 
tips of ears
vasculitis/opathy
juvenile cellulitis - young puppies - 
affects muzzle, face, sometimes ears, tx steroids, noninfectious dz.

sterile eosinophilic pinnal folliculitis
relapsing polychondritis - dz of 
cats in which ear cartilage degenerates
ear margin seborrhea - most 
common in spaniels, keratinization disorder

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