ACCREDITED CPD - DERMATOLOGY
ment is as for O. cynotis.
Foreign material may be grass awns, grass seeds or
ticks as well as certain irritant topical agents. Atopy,
cutaneous adverse food reactions, and contact hypersensitivities frequently play a mayor role.
Sensitivity to otic preparations may occur, although
this is rare. Keratinization disorders include seborrhoea and endocrine disorders causing otitis include
hypothyroidism, hyperadrenocorticism and sex hormone imbalance. Auditory polyps occur in both the
canine and the feline, although they are extremely
rare in dogs.
Figure 1. Typical appearance of otitis externa
a hirsute (Fig 2a,b) or stenotic meatus, and pendulous
pinnae. Excessive moisture occurs in dogs that swim.
Systemic disease such as immunosuppression, renal
disease, hepatic disease, and in cats, FeLV and FIV infection, may predispose to otitis.
There is increased risk for tumours in pets with a history of chronic otitis. Benign or malignant tumours
can develop in the external ear canal of dogs and cats,
and arise from the apocrine or ceruminous glands
that line the ear canal. The most commonly encountered tumour is the ceruminous gland adenocarcinoma and is more commonly seen than adenomas in
both dogs and cats.
Primary causes
These include parasites, foreign material, hypersensitivity, neoplasia, polyps, keratinization disorders, and
endocrine disorders.
Hypersensitivity is a very common underlying cause of
otits externa, even if only one ear is affected. Animals
such as golden retreivers and German Shepherd dogs
have the most perfect anatomy - wide open canals,
minimal hair in the canal and in GSDs' upright ears yet they are predisposed to otitis. It’s because they are
predisposed to allergic disease: atopy or food allergic
dermatitis. Often just managing this underlying cause
will cause resolution of the otitis. Without managing the allergic disease the otitis will be recurrent and
chronic changes will develop in the ear canals which
will perpetuate the problem. Parasites include mites
(Otodectes, Demodex, Sarcoptes), ticks (Otobius) and
biting flies (Stomoxys calcitrans). Otodectes cynotis
(Fig 3) the ear mite of dogs and cats, spend their entire
3-week life-cycle deep in the ear canal of the host.
Otoscopic examination reveals these long-legged
mites. The mites produce a marked reaction which
is probably allergic in origin. Dogs shake their heads,
which may lead to the formation of othaematomas.
The tympanic membrane may perforate, leading to
otitis media and nervous symptoms.
A roll smear of ear canal debris often reveals pathogenic organisms. Demodex infestation may intra- or peri-aural. Acaricides (e.g. benzyl benzoate
and thiabendazole) can be inserted into the ear canal. Spot-ons containing acaricides (e.g. moxidectin,
milbemycin, eprinomectin or selamectin) are advised
concurrently, since the mite will often be found in the
peri-auricular regions. Otobius megnini, the spinose
ear tick, may occasionally invade cats’ ears. Manage-
Figure 2a. Schnauzers and Poodles typically have a lot of hair
lining the ear canal.
Figure 2b. Otoscopic view of an ear canal with a lot of hair
showing how plugs form within the ear canal.
vet360
Issue 02 | APRIL 2016 | 20
April 2016 Vet360 for Madaleen Review.indd 20
2016/03/24 2:24 PM