Otitis externa is inflammation of the outer ear canal.
What is the cause?
There are many primary causes of otitis externa including :
* Atopy - one of the commonest causes of otitis externa
* Food hypersensitivity (80% of affected cats and dogs reported to have otitis)
* Contact hypersensitivity
* Autoimmune disorders
* Pemphigus foliaceous
* Diseases of glands in the skin
* Hyperplasia of glands reported in Cocker Spaniels
* Foreign objects in the ear canal
* Grass awns
* Excessive hair
* Sand, soil, water
* Generalised diseases of keratinisation
* Primary idiopathic seborrhoea
* Hormonal disorders - hypothyroidism, sex hormone imbalances
* Ear mites (eg otodectes cynotis) - one of the commonest causes in cats (50%) and dogs (10%)
* Flies, ticks and fleas
* Canine distemper virus has been implicated
* Other causes
* Eosinophilic infiltration of the pinna
What breeds is this seen in?
Animals with narrow auditory canals and flop ears are more likely to develop otitis externa than others. Cocker spaniels may develop glandular hypertrophy and German Shepherd Dogs are reported to have an increased predisposition. Working dogs and pet dogs that are exercised in rural areas are more likely to get grass awns and other vegetative foreign objects in their ears.
What are the signs?
There are many signs including :
* Reddening of the skin of the pinna
* A visible, often smelly, discharge in the outer ear canal. This can be any colour from black, brown, red-brown, red, yellow, to off-white.
* Head shaking
* Scratching at the affected ear(s)
* Drooping of the affected ear
* Pain when eating (if complicating otitis media involves tempero-mandibular joint)
* Holding the head to one side, (to the side of the affected ear)
* Walking in circles
* Fitting - if complicated by otitis media/interna
* Bacteria and yeasts are common secondary infections (they are rarely a primary cause). Chronic otitis externa leads to thickening of the skin of the pinna, with hyperplasia, hyperkeratosis, fibrosis and calcification. Swelling of the tissues closes off the auditory canal leading to reduced natural ventilation.
If the tympanic membrane is diseased or ruptured otitis media may develop with osteomyelitis.
How to diagnose
Thorough examination of the external ear canal with an auroscope is necessary to identify the presence of a foreign object. To get good visibility may require cleaning the wax and debris out of the canal and a general is needed in some cases to get good visibility of the horizontal canal and tympanic membrane.
Other diagnostic tests that may be helpful include :
* Cytological examination of the discharge in the ear canal
* Culture an sensitivity testing of swabs taken from the canal
* Biopsy and histopathological examination
There are several forms of treatment:
* Cleaning - use proprietory ceruminolytic product
* Removes foreign material and objects
* Removes excessive wax and other secretions as well as cellular debris
* Flush with sterile physiologic saline solution
* Polytherapy products are often used topically in the ear canal to treat otitis externa. These are usually given as oil-based drops or creams and include a combination of some or all of the following :
* Antiparasitic agent
* Corticosteroid - glucocorticoids for their anti-inflammatory and antipruritic effects.
* Antifungal agent
* Systemic antibiotics or corticosteroids have been reported to be helpful to treat otitis media.
In chronic otitis externa the external ear canal can become so narrow that the condition cannot be managed successfully with medications alone. In such cases surgical intervention may be needed - aural resection (opening of the lateral side of the vertical canal) or, in the worst cases vertical canal removal (ablation) or total removal of the external canal.
Bulla osteotomy is needed to treat persistent or recurrent otitis media.
What is the Prognosis?
Good if treated early. Guarded with chronic otitis externa ..can have a protracted course and .may result in surgery being needed.
What are the long term issues?
Hearing loss and recurrences are common