Otitis externa

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Otitis externa

Introduction

Otitis externa, or inflammation of the external ear canal,
is a common condition in dogs and cats. It is characterized
by inflammation of the soft tissue components of the
external ear canal and is particularly prevalent in dogs
with long, floppy ears.

ear-dog 

Left: as
demonstrated by the above ear-model, the ear canal has a
vertical and a horizontal component. This predisposes the
animal to ear infections as debris must work its way upward
rather than straight out.

Right: otitis externa with brown exudate

Anatomy of the
ear


The ear of the dog and the cat is composed of three parts:
the external ear, the middle ear and the inner ear.
Together these components allow the animal to locate a
sound and the direction from which it emanates, to
orientate the head in relation to gravity and to measure
acceleration and rotation of the head.

Selective breeding, of dogs in particular, has resulted in
a wide variation in relative size and shape of the
components of the external ear. Compare, for example, the
French Bulldog, the Cocker Spaniel, the German Sheperd Dog,
the St. Bernard and the Persian cat. The pinnal shape and
carriage, the diameter of the external ear canal, the
degree of hair and amount of soft tissue within the
external ear canal, and the shape of the skull within which
the middle and inner ear lie vary from one breed to
another.

The
external ear canal


An importrant difference between the tissues of healthy
ears and infected ears is the appaerance and distribution
of the glandular structures. In a healthy ear, sebaceous
glands are usually numerous , large and actively secreting.
In chronic otitis externa, they are less active and much
smaller. The external ear canal may normally contain a
small amount of wax that is yellowish-brown in color.

Signs of
ear disease

Every day we see
dogs and cats who have problems with their ears. Signs of
these ear problems include:

• Odor

• Scratching or rubbing of ears and head

• Discharge in the ears

• Redness or swelling of the ear flap or canal

• Shaking of the head or tilting it to one side

• Pain around the ears

• Changes in behavior such as depression or irritability

Causes of
ear disease


Allergies such as
atopy or food allergies

Parasites – ear
mites. Adult mites are large, white and free-moving. the
life cycle of the ear mite is three weeks. Mites are
characterized by thick, reddish-brown or darkbrown exsudate
and crusts in the ear. Ear mites are the single most
frequent cause of otitis externa in the cat. Mites are
highly contagious.

Bacteria and Yeast
infections
. Staphylococcus or Streptococcus
(Gram-positive bacteria) infections are most frequently
associated with acute otitis externa. There is a
light-brown, creamy exudate. Gram-negative organisms
(Proteus, Pseudomonas, E.Coli) are most frequently observed
in chronic otitis externa or recurrent ear disease. There
is a yellow exudate. Malassezia canis is a budding yeast: a
brown, waxy adherent exudate.

Ticks. The spinous
ear tick is found in the external ear canal of dogs and
cats. The ear canal become packed with immature ticks.
Treatment involves mechanical removal, spraying or dipping
the coat with an insecticide.

Foreign bodies, e.g.,
plant awns

Trauma

Hormonal
abnormalities
, e.g., hypothyroidism

The ear environment,
e.g., excess moisture and ear anatomy

Hereditary or immune
conditions


Tumors

Treatment

The first step in otitis externa is a thorough cleansing of
the ear canal followed with irrigation of the canal with a
warm antiseptic solution (chlorhexidine or betadine). A
warm sterile solution should be used if there is any
indication of ruptured membrane.

Most topical ear medications are combinations containing
one ore more antiparasitics, antibacterial, antimycotic,
anti-inflammatory, local anesthetic, ceruminolytic and
drying and cleaning agents. Oil or ointment bases help
moisturize the skin and are effective in dry, scaly or
crusty lesions. Solutions or lotions are most frequently
used in exsudative ear lesions.

Cotton applicator swabs can be used to clean the inside of
the earflap and the part of the ear canal you can see. They
should NOT be used farther down in the ear canal since that
tends to pack debris in the ear canal, rather than removing
it!

Chronic otitis externa is usually associated with
underlying skin conditions such as seborrhea,
hypothyroidism or improperly or neglected ear disease.ar
problems caused by a systemic disease such as a hormone
abnormality or allergy must include a therapy that treats
the whole dog, such as hormonal replacement or allergy
testing and hyposensitization (immunotherapy).

Surgical
treatment

Depending on the severity of the problem,
the vertical canal may need to be opened surgically. This
enables debris to be removed more effectively. This is done
to prevent severe scarring after prolonged specific medical
therapy has been ineffective. This procedure is called a
lateral ear resection. There are several surgical
techniques for this surgery.

If the canal becomes so scarred that it is practically
closed, ablation may be the final option. In this surgical
procedure, the entire ear canal is removed and healthy
tissue is allowed to grow in. This procedure is a last
resort after severe infection has made effective medical
treatment impossible. A specialist is called in for these
cases and although surgery is expensive, dogs with chronic
severe otitis usually require no further ear treatment for
the rest of their lives.



Aural
hematoma



Complication of ear
disease:
aural hematoma

When a dog or cat with uncomfortable ears shakes and
scratches vigorously, a blood vessel in the ear flap may
rupture.  This leads to bleeding into the tissues of
the pinna (see above illustration). The usual
recommendation is to have the blood clots removed and the
ear bandaged and cleaned under anesthesia. If the hematoma
is not so big as to occlude the ear canal (thus preventing
medication), the option to forgo surgery exists; but
without surgery, the ear may scar down into an abnormal
appearance.

Preventing
ear disease

The key to healthy
ears is to keep them clean. Check your cat’s and dog’s ears
weekly. A slight amount of waxy buildup may be present in
normal ears. If your dog swims a lot, has pendulous ears,
or a history of ear disease, routine cleaning (often once
to three times per week) is recommended. Use the same
procedure as described above. Excess hair around the ear
can be clipped to allow more air flow. Treat any underlying
condition that predisposes your dog to ear problems.

Remember, if your dog or cat is showing severe discomfort,
the ears have a bad smell, or the ear canals look very
abnormal, do not delay in contacting your veterinarian. If
your dog has a ruptured or weakened eardrum, some ear
cleansers and medications could do more harm than good.




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