Download CANINE OTITIS- WHAT WE CAN LEARN FROM CHALLENGING

CANINE OTITIS- WHAT WE CAN LEARN FROM CHALLENGING CASES
Alison Flynn-Lurie
Miami Veterinary Specialists
Background information is provided in the lecture notes. The lecture will highlight the key
points using a case based format.
Etiologies of Otitis:
A. Predisposing factors - factors that place the patient at risk of developing otitis. Many dogs
have these, not all dogs experience otitis.
B. Primary factors - factors that directly incite the otitis. If you can treat/ control these factors, the
otitis resolves.
C. Secondary factors - factors that contribute to or cause pathology, only in the abnormal ear, or
in combo w/ the predisposing factor or primary disease
D. Perpetuating factors - factors that prevent the resolution of the otitis.
A. Predisposing Factors
1)
Pendulous Ears
2)
Excessive hair on pinna (cockers) or in canal (poodles)
3)
Stenosis of the ear canal (Chinese shar pei, chow-chow)
4)
Climate temperature and humidity
5)
Excessive cerumen production. Sebaceous gland and hair follicle density (Cocker Spaniels,
Springer Spaniels, Labradors)
6)
Increased moisture- (excessive swimming or bathing)
a)
Additional moisture causes rehydration of the corneocytes and breaks downs the protective lipid
barrier of the stratum corneum, which allows opportunistic microbes to colonate in the canal
b)
Think maceration
7)
Excessive ear cleaning and vigorous hair plucking
8)
Obstructive ear disease (can be primary factor too)-neoplasia, polyp
9)
Systemic diseases-FeLV, FIV, Parvo, distemper
B. Primary Factors
1)
Parasites
a)
Otodectes cynotis is a nonburrowing psoroptid mite and an obligatory parasite. These mites
make up 50% of cases of otitis externa in cats and 5-10% in dogs. Otodectes infestation is more
common in dogs and cats less than 1 year of age. They can survive on the skin surface in areas such
as the head and neck. Within the ear canal the mites are protected from desiccation by thick dark
brown crust. They feed on lymph and whole blood from the ear canal epithelium, causing irritation of
the ceruminous glands.
b)
Otobius megnini is a spinous ear tick of dogs that is prevalent in the Southwestern US. The
parasitic larvae and nymphs induce a severe inflammatory reaction in the ear.
i)
Left untreated, larvae remain in the canal for 7 months before molting into the nymphal stage,
then dropping to the ground and maturing into the non-parasitic adult.
c)
Other parasites that can be found in the ear canal are Sarcoptes scabiei, Notoedres cati,
Eutrombicula alfreddugesi (chiggers) and Demodex cati and canis.
2)
Foreign Bodies
a)
Dogs with foreign bodies typically present with unilateral otitis. Various foreign bodies have been
incriminated. Plant awns (fox tails), dirt, stones, impacted wax, loose hair, and concreted otic preparations (i.e.
Otomax). They are often difficult to identify because they become coated with cerumen. Anesthesia and
thorough examination may be required for identification and removal.
3)
Intraluminal Tumors
i)
Tumors are relatively uncommon in the dog and cat.
ii)
By causing obstruction, the tumor may inhibit normal clearing of otic debris, leading to irritation
and secondary infection.
iii)
The tumors may be either malignant or benign.
iv)
Ceruminous gland tumors are the most common ear canal tumors in the dog and cat. The most
common malignant tumors are ceruminous gland adenocarcinoma and squamous cell carcinoma.
These tumors can become ulcerated and necrotic. Cats have higher incidence of malignant tumors
than dogs.
v)
In young cats, inflammatory polyps are common.
4)
Hypersensitivities
a)
Atopic Otitis
i)
Approximately 50% of atopic dogs have bilateral otitis externa, and in 5% it may be the first and/
or only symptom.
ii)
In uncomplicated, allergic otitis you may note mild to moderate erythema of the pinnae and
vertical canal while the horizontal canal remains normal.
iii)
With progression there is often erythema, inflammation and secondary infection throughout the
entire canal.
b)
Food Allergic Otitis
i)
80% of dogs diagnosed with food allergies are diagnosed with otitis.
ii)
20% of food hypersensitivities will present with otitis as the initial and/or only sign.
iii)
Food allergy is a top differential for chronic otitis externa in a young dog (<1 year of age) or in an
older dog with acute onset of otitis without previous history of ear infections.
c)
Contact Allergic Otitis
i)
Any product introduced into the ear canal can cause contact hypersensitivity.
ii)
The most common products incriminated are neomycin and otic formulations that contain
propylene glycol.
iii)
Clinically you will often note pinpoint papules, severe erythema, ulceration, and pain upon
administration of the product.
iv)
Degenerative neutrophils are a common cytologic finding, often the infection has resolved and
no microorganisms are found.
v)
If suspected, the topical product should be discontinued immediately.
vi)
Steroids should be considered in severe cases.
5)
Disorders of Keratinization
a)
Primary idiopathic seborrhea
i)
In this disease there is significant hyperkeratosis of the epidermis and hyper-proliferation of the
sebaceous glands.
ii)
There is an increase in epidermal free fatty acids and a decrease in epidermal diester waxes.
This results in increased cerumen production, altered cerumen composition, delayed desquamation,
and stenosis of the ear canal.
iii)
Secondary bacterial or yeast infections result.
6)
Endocrine disease
a)
Hypothyroidism
i)
Dogs with hypothyroidism have an increased mucin deposition within the dermis, hyperplasia,
and hyperkeratosis of the epidermis.
ii)
Alterations in the quality and quantity of fatty acids within the ceruminous debris occur.
iii)
Secondary bacterial or yeast infections of the skin and ears result.
7)
Autoimmune Disease
a)
Pemphigus foliaceus (PF)
i)
PF is type II hypersensitivity reaction that targets desmoglein 1, a transcellular protein important
for keratinocyte cohesiveness and stability.
ii)
iii)
b)
i)
Subcorneal pustules are the primary lesion and occur on the skin and within the ear canals.
Secondary bacterial and yeast skin and ear infections may occur.
Juvenile Cellulitis
Juvenile cellulitis is a vesiculopustular disease seen in puppies most commonly between 3-16
weeks, but can be diagnosed in older dogs.
ii)
The etiology is unknown, and may be related to a hypersensitivity reaction and/or viral disease.
iii)
Dachshunds, golden retrievers and pointers are over-represented.
iv)
Head and facial lesions including purulent otitis, blepharitis and regional lymphadenopathy result.
v)
Secondary bacterial and yeast infections arise in the ears and skin.
C. Secondary Factors
1)
Bacteria
a)
Staphylococcus sp, Micrococcus sp and occasionally coliforms are the most common
commensal bacteria cultured from normal canine ears.
b)
The most common isolate in canine otitis is Staphylococcus intermedius (30-50%).
Staphylococcus spp. in low numbers can be found in a normal ear.
c)
Others- usually pathogenic:
i)
Proteus mirabilis
ii)
Coagulase-negative Staphylococcus sp
iii)
Beta hemolytic Streptococci
iv)
Pseudomonas auruginosa
v)
vi)
Corynebacterium sp
Escherichia coli
2)
Yeast
a)
Malassezia pachydermatis is the most common yeast in the dog and cat.
i)
It is isolated in 49% of normal dogs and 23% of normal cats.
ii)
It is always important to take into consideration the clinical appearance of the ear and the
patient’s comfort prior to treating an ear with Malassezia as it may be normal for that animal.
iii)
Ask yourself --is the dog head shaking, face rubbing, ear scratching, developing hot spots on the
neck, and is the ear red and inflamed? If no, then the yeast are likely to be normal flora.
D. Perpetuating Factors
1)
Pathologic changes of the ear canal
a)
Several changes of the ear canal can occur with chronic inflammation and infection.
b)
Hyperplasia, hyperproliferation and ossification of the ear canals can result in a permanently
stenotic ear that cannot be modified by aggressive corticosteroid therapy.
c)
These cases should be referred for surgical management.
2)
Tympanic membrane changes
a)
Thickening, dilation, and diverticulum are changes that may occur and prevent your ability to
adequately and appropriately assess the extent of infection in the ear.
3)
Otitis Media
a)
Much more to follow later in the notes!
Diagnostics
1. Cytology:
a.
It is important to perform cytology on ALL otitis cases.
b.
Take an ear swab of each ear, roll exudate on the slide, heat fix and stain with Diff
Quik.
c.
Assess slide under microscope on 100X.
d.
There are basically 3 types of organisms you will assess for:
1) cocci-shaped bacteria
2) rod-shaped bacteria
3) yeast
2. Culture:
To culture or not to culture…
a.
If you make the diagnosis of otitis and you have cocci-shaped bacteria, 99.9% of
the time this is a Staphylococcus intermedius otitis externa.
i.
You do not need to culture this ear unless rod-shaped organisms are
seen on the slide.
ii.
An exception would be if you are already treating appropriately for
Staphylcoccus intermedius, yet not seeing a positive response.
b.
Methicillin-resistant Staphylococcus intermedius or shleiferi will not respond to
cephalexin, cefpodoxime (Simplicef), or amoxicillin-clavulanate (Clavamox). These
resistant organisms are commonly sensitive to only clindamycin, trimethoprim-sulfa, or
chloramphenicol.
c.
Stop all therapy for at least 72 hours prior to culturing.
3. The clinical diagnosis
a.
If you make the clinical diagnosis of otitis and you note rod-shaped bacteria
(especially bipolar rods) on cytology, it is imperative that you culture to rule in or out
Pseudomonas otitis media, or other highly resistant gram negative infections.
b.
If you make the clinical diagnosis of otitis and you note yeast organisms, you do
not need to culture.
*One very important concept to remember is that you may be dealing with one organism in the
external ear and a completely different organism behind the tympanic membrane in the middle ear.
When you have a dog or cat under anesthesia for a deep ear flush you will need to repeat cytology
following the myringotomy. There may be cocci-shaped bacteria on external ear cytology and rodshaped bacteria in the middle ear following myringotomy.
Treating Otitis externa:
Treatment of external ear infections depends on identifying and controlling the predisposing
factors and primary causes whenever possible. In other words, if you do not control the food
allergy, or the atopic disease, or the pemphigus foliaceus, you will not control the Otitis Externa!!
Topical therapy will always be required utilizing both a flush and an anti-microbial product. There are
numerous products on the market and new ones are developed regularly.
Otitis externa requires a minimum of 3 weeks of topical antibiotics and/or antifungals depending on the
organism and culture results. Topical corticosteroids are often incorporated into topical products; they
help decrease inflammation, discomfort, and stenosis of the canal. Corticosteroids also decrease
exudate production into the ear canal. The steroid is not always necessary for otitis externa, often
times therapy for the infection is all that is needed to make the patient significantly more comfortable.
For example, Malassezia otitis is often associtated with significant erythema and discomfort. A current
favorite product is Conofite® (Miconazole 1%), this product has no steroid and simply treating the
infection resolves the discomfort.
Ultimately, the treatment is tailored to the individual case, based on cytology, appearance of the ear
canal, and comfort of the patient. A few currently available products include:

Malacetic® (Dermapet)

Epiotic® (Virbac)

Alocetic otic® (DVM)

Oticlens® (Pfizer)

Oticalm® (DVM)

Otipan®
Systemic therapy is indicated for if Otitis Externa is severe, marked proliferative changes are
present, or owners can not administer topical treatments. Appropriate antimicrobials should be given
until at least 1 week after cure, at minimum 4 weeks.
For systemic therapy:

Cephalaxin: 30 mg/kg/BID

Clavamox: 20 mg/kg BID

Simplicef: 10 mg/kg/day

Clindamycin: 11 mg/kg/BID

Others based on culture and sensitivity
Parasiticidal agents
Contain pyrethrin: Otomite plus®, Cerumite®, Mita-Clear®, Otic-Care®
Contain rotenone: Ear Mitecide®, Ear mite lotion®
Contain thiabendazole: Tresaderm®
Remember to treat all in contact animals.
Remember that whole body therapy may be needed (ie Otodectic & Notoedric mange), consider
Selamectin (Revolution®) or Ivermectin (not approved for Otodectes in US and caution with certain
breeds and kittens).
Monitoring therapy
Explain to the owner how important a follow up exam and cytology are. The owner will almost always
think the infection is resolved, of course they will, you identified the infection correctly and treated
accordingly. Additionally, if the product you prescribed contained a steroid, the ear will definitely
improve simply from the anti-inflammatory effects. Recheck at 2 weeks, it is always wise to treat 7
days past resolution of signs.
OTITIS MEDIA
Otitis Media is inflammation +/- infection of the middle ear. Causes include:
1) Extension of otitis externa
2) Infection ascending through the eustachian tube
3) Hematogenous spread of infection
Otitis media must be suspected in chronic recurrent, relapsing otitis externaIt is often difficult to
diagnose by otoscopic exam alone, as stenotic changes and exudates within the ear canal obscure
visualization of the tympanic membrane.
Radiographs can be helpful, especially in chronic cases.
However, radiographs may not show evidence of otitis media in up to 25% of surgically confirmed
cases. MRI and CT-scans are more sensitive, but not readily available to all practitioners and are still
susceptible to false negative and false positive results.
In dogs, otitis media occurs in approximately 16% of acute otitis externa cases and up to 84% of
chronic recurring cases. Otitis media should be suspected if there is a history of relapse within days to
weeks following appropriate therapy for otitis externa.
If a patient presents with peripheral neurological signs including vestibular disease, Horner’s
syndrome and/or facial nerve paralysis, assessment of a middle/ inner ear infection is imperative.
Diagnosis of otitis media via external ear canal examination is not always easy. The ear canal of the
dog is long, and stenosis or otic debris can obstruct the view of the tympanic membrane. A normal
tympanic membrane appears translucent and the attachment of the malleus inside the tympanic bulla
should be visible. If you observe the tympanic membrane on otoscopic examination, assess for
abnormalities such as opacity, scarring or bulging. These findings may indicate the tympanic
membrane has been ruptured in the past or there is active otitis media. It is important to note that
otitis media can be present in the face of an intact tympanic membrane. Commonly, a dog may
present to the veterinarian with otitis. The lack of an intact tympanic membrane may be missed due to
inflammation, purulent debris, and stenosis of the ear canal. Topical therapy is instituted for otitis
externa. With treatment the infection improves, and the tympanum may re-grow. The dog now
appears to have responded to topical therapy. Unfortunately, the middle ear remains infected and will
fulminate, causing rupture of the tympanum and relapse of the symptoms of otitis externa within days
to weeks.
The following scenarios should raise your suspicion to the presence of otitis media:
1. A history of chronic, relapsing otitis (relapse rate of days to weeks)
2. Inability to visualize the tympanic membrane on otoscopic exam
3. Clinical signs and cytologic results compatible with Pseudomonas otitis
4. The presence of peripheral neurologic symptoms (vestibular disease, facial paralysis, Horner’s
syndrome)
Neurologic complications (Peripheral or Central)
Dogs and cats can present with peripheral neurologic disease with or without an obvious otitis. Cats,
more often than dogs, can develop otitis media/interna via the eustachian tube due to an upper
respiratory infection or a nasopharyngeal polyp. In these cases the tympanic membrane may be
abnormal (bulging, opaque), but signs of otitis externa may not be present.
Only a minority of cases with otitis media present with neurologic symptoms. However, some patients
with otitis media have neurologic symptoms. Differentiating between a peripheral and a central
neurologic deficit can be challenging is some cases. The patient with middle/inner ear disease may
present with facial nerve paralysis, vestibular disease (i.e. head tilt, nystagmus) and/or Horner’s
syndrome (miosis, enophthalmos, ptosis, and protrusion of the third eyelid). Diseases of the
middle/inner ear can cause injury to the vestibular receptors of the membranous labyrinth.
Peripheral vestibular disease is characterized by ataxia and loss of balance, with preservation of
strength. Despite the ataxic gait and tendency to fall, strength and proprioception are preserved with
peripheral lesions. Animals with peripheral vestibular disease are typically alert and have normal
mentation. Nausea and vomiting may be present because of the connection of the vestibular system
to the vomiting center. Cranial nerves that run through the middle and inner ear can become inflamed,
the animal may present with variable cranial nerve deficits. A head tilt and nystagmus can be seen
concurrently or alone. Typically, if you have a patient with peripheral neurologic deficit, the animal will
show neurologic signs on the same side of the lesion (ear infection) without other central neurologic
deficits (hypometria, hypermetria, altered mentation or proprioceptive deficits).
With central lesions the head tilt is opposite to the lesion. There is an exception to this rule when
assessing head tilt: If a central lesion is affecting the vestibular nerve at the level of the medulla you
may see a head tilt toward the lesion, but this patient will have additional neurologic deficits (i.e.
proprioceptive deficits).
Nystagmus in peripheral disease is usually horizontal or rotary, but in central disease nystagmus is
more commonly to be vertical, positional or rotary. However, these are not reliable indicators. A dog
with central vestibular disease will exhibit additional neurological symptoms such as proprioceptive
deficits, hemiparesis, or quadriparesis which may support a brainstem lesion. Head tremors,
hypermetria, or hypometria would provide evidence of a cerebellar lesion.
Facial paralysis commonly accompanies middle and inner ear disease. The facial nerve exits the
cranial vault through the internal acoustic meatus accompanied by the vestibular and cochlear nerves.
From the meatus, the facial nerve runs through the petrous temporal bone and through the middle
ear. The motor portion of the facial nerve supplies the superficial muscles of the head and face. The
facial nerve also supplies preganglionic parasympathetic fibers to the lacrimal gland and salivary
glands. Therefore, diseases of the inner ear may damage the facial nerve, resulting in ipsilateral facial
paralysis. Patients may present clinically with ear, lip, and eye droop on the affected side. Over time
chronic nerve damage leads to contracture of the facial muscles. Owners may complain that the dog
may drool excessively or drop food from the affected side. Palpebral, menace and corneal responses
are reduced due to the inability to close eyelid. Neurogenic keratoconjunctivitis sicca (KCS) is often
associated with middle ear disease and can be mistaken for an autoimmune etiology. Once the ear
infection is treated, the KCS will resolve.
Horner’s syndrome may be seen in patients with middle ear disease. Sympathetic innervation to the
eye arises from specific spinal cord segments. Preganglionic sympathetic fibers pass through the
thorax and neck and synapse in the cranial cervical ganglion deep to the tympanic bulla.
Postganglionic fibers pass into the middle ear and run along the tympano-occipital fissure and join the
ophthalmic nerve. Sympathetic fibers innervate smooth muscle that lifts the eyelids, pulls the eyes
rostrally, retracts the third eyelid, and dilates the pupil. Clinically miosis, enophthalmos, ptosis, and
protrusion of the third eyelid may be seen on the same side as the infected middles ear.
You have diagnosed otitis media/interna…now what?
Many dermatologists who routinely treat otitis feel that the most important procedure following
diagnosis of otitis media/interna is anesthesia and deep ear flush after myringotomy (purposeful
rupture of the tympanic membrane). Treating solely with systemic antibiotics/antifungals and topical
ear products will often result in therapeutic failure.
Treating Otitis Media:
Treatment of middle ear infections requires a minimum of 6-8 weeks of systemic antibiotics and/or
antifungals depending on the organism and culture results. Topical therapy is directed at the
organism(s) identified through culture. Topical corticosteroids (Synotic®) and/ oral prednisone (0.5
mg/kg/QD to BID in a tapering dose over 10-14 days) is often indicated to decrease inflammation,
discomfort, and stenosis of the canal. Corticosteroids also decrease exudate production into the ear
canal. The treatment is tailored to the individual case, based on cytology and culture results,
appearance of the ear canal, and comfort of the patient.
Staphylococcus intermedius Otitis Media:
For systemic therapy ideally based on culture/ sensitivity: given for minimum of 6-8 weeks. If cultures
are not available:

Cephalaxin: 30 mg/kg BID

Clavamox: 22 mg/kg BID

Simplicef: 10 mg/kg/ SID

Clindamycin: 11 mg/kg BID
For topical therapy, cleaners:

Malacetic® (Dermapet)

Epiotic Advanced® (Virbac)

Alocetic otic® (DVM)

Oticlens® (Pfizer)

Oticalm® (DVM)
Have the owner use one of the above products as a flush at home, this helps remove residual
medication from the canal, providing a “clean” canal into which the true anti-microbial medication can
then be placed. Once daily should suffice. Instill a moderate amount into the ear, massage well, wipe
with cotton, and allow animal to shake.
Follow 10-15 minutes later with the appropriate topical antibiotics:

Tresaderm (Neosporin, thiobendazole, dexamethosone) 6-8 drops twice daily

This is the best choice of topicals based on current available products

Baytril Otic (Enrofloxacin, Silver sulfadiazine)

Silver sulfadiazine 1% solution
Malassezia pachydermatis OM:
Systemic medications:

Ketoconazole 5 mg/kg BID (avoid in cats due to nausea and vomiting)

Itraconazole 5 mg/kg/day (better tolerated but expensive in large dogs)

Fluconazole 5 mg/kg/day
Topical therapy:

Cleaner: Malacetic® (Dermapet), Epiotic®, Alocetic otic®, or white vinegar/H2O (50:50) Instill
moderate amt into the ear, massage well, wipe w/ cotton, allow to shake.

Drops: Conofite® (Miconazole 1%), or Lotrimin® Solution (Clotrimazole 1%) - Apply 6-8 drops
into affected ear twice daily.
Rod-shaped organisms, almost always a sure sign of OM! ALWAYS SELECT ANTIBIOTIC
BASED ON CULTURE RESULTS!
Systemic medications:

Enrofloxacin 20 mg/kg/day-on empty stomach for best absorption. Avoid in cats-Blindness!!!

Ciprofloxacin 30 mg/kg/day--on empty stomach for best absorption. Avoid in catsBlindness!!!

Marbofloxacin 5 .5 mg/kg/day--on empty stomach for best absorption.
Topical treatment, cleaner:
Triz-ETDA® (Dermapet) or T-8 Solution® (DVM) –Instill generous amount, allow 5-10 minute contact
time, allow dog to shake head, and wipe with cotton or tissue. I usually have clients wait 2-3 days
after the deep ear flush/myringotomy to start the flush depending on the discomfort of the ear before
starting to flush at home. This flush should be done twice daily 10-15 minutes prior to instilling the
anti-microbial product. These products work as chelating agents, essentially punching holes in the
membrane of the microbe, allowing better penetration of the anti-microbial product.
Topical antibiotics for empirical treatment of Pseudomonas otitis:

Neomycin, Polymyxin B, Hydrocortisone 1% (Cortimycin)

Silver sulfadiazine 1 % solution

Bayril injectable (used as topical)

Gentamicin injectable (used as topical) (Caution for ototoxicity)

Amikacin injectable (used as topical) (Caution for ototoxicity)

Ticarcillin injectable (used as topical)
Monitoring therapy:
The patient should be rechecked every 2 weeks. Owners should see a steady improvement in the
next 6-8 weeks. An increase in discomfort, redness, discharge should prompt a call from the owner.
The complications that arise following the start of treatment include: 1) resistant organism, 2) new
organism, or 3) contact hypersensitivity to ear medications (i.e. neomycin, PPG).
If excessive amounts of exudates remain within the ear canal at recheck, repeat anesthesia and deep
ear flush. The presence of purulent debris within the ear canal can inactivate antibiotics and can
serve as a nidus for relapsing infection. It is not uncommon to repeat the ear flush at least once.
The systemic medications should be continued for 6-8 weeks regardless. You may see re-growth of
the tympanic membranes at 2 or 4 weeks and your ear cytology may be negative. In spite of this,
systemic therapy should be carried through in order to appropriately treat the middle ear.
Topical antibiotic/antifungal therapy is discontinued at 4 weeks if the following criteria I are met: 1)
tympanic membranes visualized as completely re-grown 2) ear canal is without erythema and
inflammation 3) ear cytology is negative.
Ear cleaning is either discontinued or decreased from a daily routine to 1-2 times per week depending
on the individual case and your assessment.
Tips on how to maximize the successful therapy of otitis:
1. Know your patient’s history
2. Make a list of all predisposing, primary, secondary, & perpetuating factors
--Address each one of those factors in a timely manner
3. Know what type of infection you are treating. Culture when appropriate
4. Know what is in the medication you prescribe
--Do you need gentamicin for a Staph otitis?
à the answer is NO, it is best used for gram (-) infections
--Do you need a potent steroid like betamethasone?
à the answer is likely NO, unless there is severe stenosis
5. Treat topically for the appropriate length of time:
--Prescribe a flush and an antimicrobial agent
6. Treat systemically with the appropriate drug, drug dosage, and length of time
7. Recheck your patient: an owner’s observation is not a substitute for cytology and otoscopic
exam
Not all cases go as planned, refer early for a better chance at resolution and to avoid a surgical
resolution.