WITH grass seed season upon us,
cases of acute onset otitis externa
will start to ood through the door,
and most of the time the problem
is easily solved by removal of the
offending foreign body.
Unfortunately, treating cases of
chronic or recurring ear disease is not
always that simple and can sometimes
be the source
of a client’s
discontent
when this
seemingly
simple issue
(in the eyes of
the client) just
won’t go away.
The Webinar Vet organised Dr Klaus
Loft to lead a webinar covering otology
in the dog and cat discussing how we
approach and best manage these cases.
Dr Loft, of Angell Animal Medical
Center (MSPCA) in Boston, has
published articles and lectured both in
Scandinavia and the United States; his
special interests are feline dermatology
and chronic ear disease.
He wanted to emphasise rstly
that a patient showing ear disease is
always a dermatology case until proven
otherwise, and a full case history is
absolutely key in deciphering whether
these patients have ever suffered any
previous dermatological episodes. Dr
Loft also stressed the importance of
performing a full clinical hands-on
examination.
The pinnae should be checked
thoroughly, the temporomandibular
joint should be manipulated for signs
of pain and the cranial nerve re exes
assessed. A thorough otoscopic
examination is essential using good
equipment.
At this stage Dr Loft expressed
concern that many cases referred to
him will often not mention being either
able or unable to visualise the tympanic
membrane. He believes that in 20-
30% of his own cases he is unable
to visualise the tympanic membrane
(perhaps there is wax in the way or the
dog won’t tolerate full examination) and it is always imperative that we note this down for comparative reasons at a
re-check.
The three Ps
When considering how to best
approach otology cases, Dr Loft
explained that we needed a good
understanding of the three Ps affecting ear disease: predisposing factors,
primary factors and perpetuating
factors.
- Predisposing factors
Predisposing factors are conditions
that facilitate and increase the risk of
inflammation within the ear canal.
Anatomy and confirmation fall under
this category with
breeds like the Shar Pei
suffering from marked
stenosis of the ear
canals.
Pendulous ears
in dogs such as the
Basset hound are also a
predisposing factor but
Dr Loft believes they are
not a causal factor for
developing inflammation in the ear, but
once inflammation has developed, this
particular design is likely to increase the
severity of the problem.
He also discussed damage to a
mechanism known as epithelial
migration which could also be a
predisposing factor. This mechanism
consists of a mixture of cellular
glands within the ear canal which grow
upwards from the tympanic membrane
as a conveyor belt of cells.
In people, if this “conveyor belt”
is damaged, perhaps by excessive
use of ear buds, ear wax will be less
effectively removed, increasing the risk
of inflammation. Although not proven,
Dr Loft believes this may also be a
problem in dogs potentially caused by
trauma such as hair plucking (a practice
Dr Loft does not recommend) or just
by us traumatising the ear canal with an
otoscope.
Other predisposing factors include
obstructive disease such as benign
and malignant neoplasia as well as
keratinisation defects such as sebaceous
adenitis, and iatrogenic causes such as
“swimmer’s” ear.
- Primary factors
Primary factors are
conditions which initiate
inflammation of the
ear canal. Cutaneous
adverse food reaction
and atopic dermatitis
fall under this category.
Usually these cases will have a history
of multiple recurring
episodes of otitis
externa and most will
have bilateral disease.
According to Dr Loft there is an
80% incidence of otitis externa in
cases of cutaneous adverse food
reaction and is seen as a single entity
with no other clinical signs in 24% of
these cases. In comparison, there is a
50-80% incidence of otitis externa in
dogs suffering from atopy and is only
seen as a single entity in 5-10% of
these cases.
Other primary factors include
foreign bodies and parasites such as
Otodectes. Dr Loft also explained that demodicosis can
cause otitis externa,
and he recommended
to always consider
this parasite especially
if a case worsens
after use with topical
steroids. Immune-
mediated disease
such as pemphigus
complex, especially in the cat, puppy strangles and erythema
multiforme are also primary factors.
- Perpetuating factors
Perpetuating factors maintain or
worsen inflammation within the ear
canal of which over-treatment and
under-treatment are two of the main
culprits.
Over-treatment such as over-use of
an ear cleaner can lead to an excess of
moisture within the ear canal and could
cause mechanical trauma.
Under-treatment, however, is the
biggest reason for failure in managing
cases of otitis. Drugs may not have
been administered for long enough and
in many cases we may just be under-
dosing.
Dr Loft explained the total length of
an ear canal can be up to 5 or 7.5cm,
especially in breeds such as the Basset
hound. This is a lot of “skin” that we need to treat and the standard 4-5
drops administered topically may just
not be enough.
Owner compliance is also key and
Dr Loft will often get owners to
administer drops twice daily just to ensure compliance,
even though
more frequent
administration may be
preferable.
Secondary bacterial
and fungal infections
are also significant
perpetuating factors and Dr Loft
recommends always
performing cytology
in any case of ear
disease.
He advises using Q tips to obtain the
sample and this should be done prior
to any manipulation of the ear canal.
Fungi, rods, cocci, inflammatory cells
and intra-cellular bacteria should all be looked for under microscopy after
performing a Diff Quick stain.
He also recommends treating as a
bacterial otitis if you see four or more
cocci per high-power eld (phpf)
and/or one or more rod phpf. He
recommends treating as a fungal otitis
if you see two to three or more yeast
phpf.
On seeing inflammatory cells, Dr
Loft always recommends using an anti-
inflammatory. He generally considers
performing a culture and sensitivity
if, after treating according to the
cytology results, rods are still present
on repeat cytology or are continuing to
increase and could raise suspicion of a
pseudomonas infection.
Culture and sensitivity is also
necessary in cases of otitis media so
these cases can be treated systemically.
Principles of treatment
Treatment of otitis externa using
topical medication is usually all that is necessary in most first line cases. The
use of cleaners to remove debris and
also alter pH is useful as well as the
topical administration of anti-fungals,
antibacterials and anti-inflammatories
according to the cytology results.
Once again Dr Loft wanted to
emphasise the point that the size of
the ear canal needed to be considered
when deciding on an appropriate dose
of topical medication.
He recommends administering 2-4
drops in the cat, 8 drops in the small
dog, 10-15 drops in the medium to
large dogs and 20 drops in the ears
of dogs such as the Basset hound.
For compliance reasons Dr Loft
recommends administering these doses
twice daily.
He uses systemic treatments in less
than 10% of first line cases but uses
it in almost all of his chronic cases.
The use of glucocorticoids to reduce
inflammation and open up the ear
canal is key and Dr Loft uses these at
a dose of 0.5mg/kg every 12 hours in
dogs and 1mg/kg every 12 hours in
cats.
He has also found oral cyclosporine
useful where there are chronic
proliferative changes, although it only
tends to be of bene t in 20-25% of
cases.
He always uses systemic treatment
in cases of otitis media and where
there has been evidence of tympanic
membrane rupture, although he
warned us that tissue penetration is
unlikely to be very good.
Summary
Dr Loft’s webinar was an excellent
insight into how we can best manage
ear disease by considering the broader
issues around this condition.
For example, the anatomy of the ear
needs to be taken into account when
considering how much medication
to administer and, as for skin, any
underlying factors such as allergic skin
disease need to be addressed.
This was a thought-provoking
webinar which looked at ear disease
from a different angle compared
to other forms of CPD I have
encountered on this subject matter and
is well worth an hour of your time.
