Otitis is an ear infection that affects both dogs and cats. Numerous factors, including bacterial or yeast infections, allergies, and parasites, might contribute to it. Otitis is a condition that affects pets frequently, especially dogs. According to studies, otitis can occur in up to 20% of dogs at some time in their life. Otitis can affect cats as well, though less frequently than in dogs. Overall, otitis is an illness that is frequently encountered in veterinary practice, and it is crucial for pet owners to be knowledgeable about the ailment's warning signs, symptoms, and risk factors.
An illustration comparing the anatomy of a dog's ear and that of humans
It's important to remember that prevalence varies depending on the geographic area, climate, and pet population under study. Overall, otitis is a problem that is frequently encountered in veterinary practice, and it is crucial for pet owners to be knowledgeable about the condition's clinical signs, symptoms, and risk factors.
What are the different types of Otitis?
In pets, there are typically three types of otitis: otitis externa, otitis media, and otitis internal.
Otitis externa refers to inflammation of the external ear canal, which is the portion of the ear that is visible and can be felt. This is the most common form of otitis in dogs and cats, and it is often caused by infectious organisms, allergies, or foreign bodies in the ear. Ear pinna (ear lobe) involvement is possible. It is one of the most common reasons that pets (particularly dogs) are taken to veterinarians. Otitis externa can be either acute or chronic, unilateral or bilateral. It is seen in rabbits too (usually due to the mite Psoroptes cuniculi) but is uncommon in large animals.
Otitis media refers to inflammation of the middle ear, which is the portion of the ear that lies behind the eardrum. This form of otitis is less common than otitis externa and is often associated with an underlying problem such as a congenital defect or a tumour though can be caused by an infection and allergies too.
Otitis interna refers to inflammation of the inner ear, which is the portion of the ear that is responsible for hearing and balance. This inflammation is also referred to as labyrinthitis. This form of otitis is the least common and is usually associated with a serious underlying condition such as a tumour or infection in the brain. The inner ear is part of the ear responsible for balance and hearing. It can be caused by a viral or bacterial infection, but can also occur due to other conditions like allergies, head injuries or exposure to loud noises. It can also be a complication of otitis media (middle ear infection).
What are the clinical signs of otitic conditions?
Clinical signs can include head shaking, pain, malodor, erythema, erosion, ulceration, swelling, and/or ceruminous gland inflammation. In the case of allergies, the clinical signs include chronic pruritus (scratching or licking), particularly of the front feet and ventral pinnae (base of the ear). If the animal suffers from hyperadrenocorticism, the animal will exhibit excessive drinking of water (polydipsia) and excessive urination (polyuria), truncal alopecia (loss of hair), thin skin and muscle weakness. For the ones suffering hypothyroidism, there will be non-pruritis (non-itching) alopecia (loss of hair) and systemic (general) signs e.g., lethargy, weight gain, poor exercise tolerance, etc.
Otitis Media
Symptoms in pets include head shaking, scratching at the ears, and discomfort or pain. In some cases, pets may also experience a loss of balance or coordination.
Otitis Interna
Clinical signs or symptoms of otitis interna can include vertigo, dizziness, nausea, vomiting, hearing loss, and/or tinnitus (ringing in the ears).
Otitis can either be an acute or chronic disease. The most typical type of otitis is acute otitis and a simple ear drop prescription is enough to prevent the infection from reoccurring. Dogs that frequently swim or have floppy ears may be more susceptible to acute otitis. Most of the time, there are no predisposing conditions.
Dogs with chronic otitis experience recurrent ear infections several weeks or months after initial treatment. These dogs receive the same initial treatment as dogs with acute otitis. The primary distinction is the need for more investigations into the underlying causes of chronic ear infections.
What causes Otitis in dogs and Cats?
Otitis is caused by numerous factors, categorized into Primary, Secondary, Predisposing and Perpetuating factors (The PSPP model). A healthy ear canal is particularly resistant to infection, with infections only arising when something "goes wrong" leading to either acute ('one time') or chronic (ongoing or recurring) otitis.
Primary causes
Primary causes of otitis externa create disease in a normal ear. They alter the environment in the ear, often allowing a secondary infection to develop. Primary causes include:
i. Allergy - atopic dermatitis (atopy), cutaneous adverse food reaction (food hypersensitivity), contact allergy (allergic contact dermatitis)
ii. Hypersensitivity reactions to ectoparasites (parasitic otitis) generally affect the ear pinna, e.g.,
a). Sarcoptes scabiei (scabies mite),
b) Flea bite hypersensitivity,
c) Otodectes cynotis (ear mites),
d) Demodex canis (mange mites),
e) Neotrombicula autumnalis,
f) Some tick species.
There are several tick species that can cause otitis (ear inflammation) in dogs and cats, including:
Otobius megnini (spinose ear tick)
Dermatocentor variabilis (American dog tick)
Rhipicephalus sanguineus (brown dog tick)
Ixodes scapularis (black-legged tick)
Ixodes pacificus (the western black-legged tick) and
Ixodes ricinus (the sheep tick).
These ticks can cause ear infections by burrowing into the ear canal and releasing bacteria and other toxins and transmitting the bacteria called Borrelia burgdorferi and Anaplasma phagocytophilum. Otitis caused by ticks can be very painful and can lead to hearing loss if left untreated.
iii. Autoimmune/immune-mediated diseases, e.g., pemphigus foliaceous, erythema multiforme. Other immune-mediated diseases affect the ear pinna, e.g., cutaneous vasculitis.
iv. Endocrine disorders, e.g., hyperadrenocorticism, hypothyroidism, sex hormone abnormalities (alopecia X).
v. Glandular disorders e.g., sebaceous gland hyperplasia, neoplasia, sebaceous gland hypoplasia, lipid-responsive seborrhea, primary idiopathic seborrhea, granulomatous sebaceous adenitis, vitamin-A responsive dermatosis, zinc-responsive dermatosis, idiopathic inflammatory/hyperplastic otitis of cocker spaniels and juvenile cellulitis.
vi. Foreign bodies, especially grass lawns.
vii. Fungal infections - dermatophytosis, aspergillosis (Aspergillus)
vii. Viral otitis - Canine distemper disease.
viii. Miscellaneous - proliferative necrotizing otitis of cats, juvenile cellulitis.
Secondary causes
Secondary causes of otitis externa create disease in an abnormal ear. These are often chronic/recurrent problems when the primary cause is not addressed and the ear canal becomes inflammed due to the primary causes. The causes include:-
Bacteria e.g., Staphylococcus, Streptococcus, Enterococcus, Pseudomonas, Proteus, etc. with acute otitis predominantly caused by gram-positive organisms especially Staphylococcus spp, Streptococcus spp and Enterococcus spp while chronic disease switch to a more gram-negative infection especially Pseudomonas spp, Escherichia coli and Proteus spp.
Yeast - Malassezia yeast disease (Malassezia pachydermatis) and Candida spp (Candida albicans) which is an uncommon cause of otitis.
Medication reactions
Overcleaning
Perpetuating factors:
Perpetuating factors are usually chronic changes to the anatomy and physiology of the ear canal as a consequence of disease otic inflammation. Unless properly managed and where possible resolved, the otitis will not respond to therapy. These factors include:
Chronic changes within the ear canal lead to epithelial changes that cause failure or alteration of migration of the ear canal epithelium. Migration of the epithelium of the ear canal provides a natural cleaning mechanism in normal ears.
Ear canal stenosis or oedema due to proliferative changes of the ear canal wall, e.g., glandular hyperplasia (apocrine or sebaceous gland), pericartilaginous fibrosis or calcification.
Tympanic membrane (ear drum) abnormality - dilation, rupture, or cholesteatoma (an ear cholesteatoma is a cyst-like growth behind the eardrum).
Chronic change within the tympanic bulla leads to otitis media. The tympanic bulla is a smooth bulbous enlargement of the tympanic part of the temporal bone which is one of the bones that form the skull and cover the middle ear.
Predisposing factors:
Predisposing factors, usually breed associated conformational problems of the ear canal anatomy, pre-exist otitis externa and increase the risk of it occurring. These include:-
Conformation e.g., pendulous ear pinna, stenotic (narrow) canals, hairy concave pinna, or excessive hair in canals. These do not cause disease in their own right.
Excessive moisture in the ear canal - swimming, bathing, humid climate.
Ear canal obstruction - polyp, neoplasia (can also be a primary cause) or feline apocrine cystadenomatosis.
Primary otitis media.
Systemic catabolic state or immune suppression.
Unnecessary overtreatment or reaction to topical treatment, eg irritation from prolonged use of topical medications, water-based products, acids, propylene glycol, and alcohol. This leads to changes in normal flora in the ear canal.
Physical or chemical damage from cleaning.
How is Otitis Diagnosed?
Otitis is diagnosed by one of the following methods:-
1. Clinical history and signs
Aural disease.
Aural pain
Head shaking or scratching the affected ear.
Otic (ear) exudate.
Pain on palpation.
Malodor.
Aural hematoma.
Acute moist dermatitis of skin over the vertical canal.
Red, hot, swollen pinna.
Pinnal scaling.
Pinnal crusting.
Bleeding from ears.
Pain eating.
Head tilt.
2. Otoscopy/video otoscopy
Otoscopy is a clinical procedure used to examine structures of the ear, particularly the external ear canal, tympanic membrane (ear drum), and middle ear. Veterinarians and clinicians use the process during routine wellness physical exams and the evaluation of specific ear complaints.
Sedation is often required for otoscopic examination and in cats and dogs with painful and swollen ear canals, it is often helpful. The changes that can be assessed with otoscopy include type and extent of exudate within the canal, proliferative changes, presence of the foreign body, ulceration of the canal, ruptured tympanic membrane, presence of ectoparasites - Otodectes cynotis mites.
3. Microscopy
Samples of exudate from the ear canal are obtained and rolled onto a microscope slide and examined after staining (Diff Quik or Gram stain) to look at cellular detail and the presence of microorganisms and unstained to check for ectoparasites (Demodex spp, Otodectes cynotis). The organisms that can be identified include bacteria, yeasts, and parasites including other findings like inflammatory cell infiltration and acantholytic epidermal cells suggestive of the pemphigus complex.
4. Bacteriology (Culture and sensitivity/susceptibility testing)
Culture and susceptibility tests are indicated when cytology (microscopy) demonstrates the presence of bacteria or where the infection has failed to respond to rational therapy on the basis of cytology and multi-resistant organisms are suspected. Culture and sensitivity testing is therefore done to help diagnose an infection. It may also help the doctor to decide which medicines to use in treating the infection. This test involves taking a tissue or fluid sample from your body and testing it to see if germs will grow in it.
5. Histopathology
Histopathology is the diagnosis and study of diseases of the tissues and involves the microscopic examination of tissues and/or cells in order to study the manifestations of disease and help clinicians to manage patients well. It involves taking a biopsy of the ear canal (rarely indicated) and can lead to the identification of neoplasia, polyps, keratinization disorders and auto-immune diseases.
6. Diagnostic imaging
a. Radiography (X-ray)
Skull radiographs are done to pick up severe chronic changes where there is calcification of the ear canal. Radiographs are rarely indicated as a diagnostic imaging modality for ear disease. Calcification can generally be diagnosed by palpation of the ear canal without the need for radiographs for the diagnosis of otitis media.
Advanced diagnostic imaging techniques are superior for the diagnosis of otitis media and otitis interna.
b. Computed tomography (CT-Scan)
CT-Scan of the head is superior to MRI scanning for otitis media.
c. MRI
MRI is the modality of choice for otitis interna. This type of scanning is important if chronic irreversible damage of the bulla is suspected and bulla osteotomy is being considered.
d. Ultrasonography
This is important for the evaluation of the middle ear.
7. Brainstem auditory evoked response (BAER) hearing testing
This test is used to detect some types of hearing loss, such as hearing loss caused by injury or tumours that affect nerves involved in hearing. Electrodes are placed on the head and certain tones or clicking sounds are made. The electrodes measure nerve signals in the brain when it reacts to the sounds. It is helpful to establish the extent of hearing that remains in an ear Hearing test.
A significant proportion of hearing loss in otitis externa is conductive loss caused by chronic changes within the ear canal that lead to canal narrowing or occlusion.
Hearing loss in otitis media is conductive due to chronic changes in the bulla and sensorineural due to damage to the inner ear caused by the ototoxic effects of drug infection.
The only reason to keep an ear canal is to allow for hearing, so if this is lost, total ear canal ablation with bulla osteotomy is recommended rather than continuing medical treatment.
What is the best treatment for Otitis?
Successful treatment is multifaceted and should include the following steps:
Primary causes of otitis externa must be identified and managed.
Ear exudate should be removed via irrigation of the ear canal
Cytologic evaluation is key to proper treatment selection.
An appropriate antibiotic from the results of culture and sensitivity should be identified and used at an effective dosage for an appropriate duration
Concurrent otitis media should be identified and treated.
Pain and inflammation must be managed in addition to infections.
Treatment should be done both topically and systemically until the infection resolves (weeks to months)
Owner education and compliance are important factors for success.
Can Otitis Treatment Fail?
The following can cause treatment failure:-
Predisposing factors
Primary and perpetuating factors not identified or treated, eg presence of otitis media, ear canal narrowed due to stenosis.
Inadequate ear cleaning before applying topical medication.
Resistance to antibiotics, especially when Pseudomonas spp is present.
Lack of cooperation from the owner or the dog, e.g., when the dog won't allow therapy or when the owner is unable or unwilling to medicate the dog. In these circumstances, it's crucial to use enough pain medication to provide the dog with comfort.
Reference
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