Chronic ear infections can represent a particular challenge; stenotic ear canals make a thorough examination of the ear canal difficult and together with the debris and discharge present in a chronically infected ear, visualisation of the tympanic membrane may be impossible. Selecting appropriate topical medication or ear cleaners can be challenging in these circumstances and if there is any doubt as to the integrity of the tympanic membrane, products with low ototoxicity should be used.
So, when are we most likely to see a ruptured eardrum in a dog? Let’s start with a brief overview of canine ear disease.
Canine otitis externa
Otitis externa (inflammation of the external ear canal) is the commonest ear disease in dogs. The causes of this frustrating condition are multifactorial, usually involving a primary underlying cause such as allergy and secondary predisposing or perpetuating causes such as microbial infections. The most common microbial agents involved in the pathogenesis of ear disease are:
- Staphylococcus species
- Malssezia pachydermatitis
- Pseudomonas aeruginosa
Most cases of otitis externa can be managed with appropriate topical therapy. Cytology plus bacteriology and sensitivity testing should be used to select an appropriate antimicrobial medication. However, many cases of otitis externa will recur if the primary underlying cause is not successfully addressed.
Canine Pseudomonas otitis
Pseudomonas otitis can be very challenging to treat. The infectious agent, Pseudomonas aeruginosa, is a gram-negative bacillus and its high capacity for becoming resistant to antibiotics can make treatment of these infections difficult.
The key to successfully managing Pseudomonas otitis is to address any underlying conditions such as allergy, select an appropriate antibiotic based on culture and sensitivity testing and clean the ear regularly and thoroughly. Successful cleaning will have a positive effect on treatment success.
Ear cleaning in dogs with Pseudomonas otitis should aim to break down the biofilm and remove purulent debris from the ear canal. The biofilm is an extracellular matrix containing bacteria and other microorganisms. It hides bacteria from the immune system, making it harder for topical antibiotics to be effective. Thorough flushing helps to physically break down this barrier.
Canine otitis media
Inflammation of the middle ear (otitis media) usually develops as a sequel to chronic otitis externa but may also occur following foreign body penetration of the tympanic membrane. The middle ear consists of the tympanic bulla, the ear ossicles and the tympanic membrane. The canine tympanic membrane is thin, pale grey and translucent in appearance.
The most common clinical signs of otitis media are:
- Head shaking
The facial and sympathetic nerves run through the middle ear so clinical signs may also include:
- Facial nerve paralysis
- Horner’s syndrome (ptosis, miosis, protrusion of the third eyelid, enophthalmos)
- Dry eye (keratoconjunctivitis sicca)
In most cases, the tympanic membrane remains intact. On otoscopic examination the tympanic membrane may appear to be bulging and discoloured but advanced imaging (CT or MRI) is likely to be required for definitive diagnosis of otitis media. Diagnosis is more straightforward in those cases where the tympanic membrane is ruptured, and a fluid-filled middle ear may be visualised.
Canine otitis interna
Otitis media can progress to inflammation of the inner ear (otitis interna). The inner ear is housed in a bony labyrinth in the petrous part of the temporal bone and contains the sensory organs responsible for hearing and balance (the semi-circular canals, cochlea and vestibule). Clinical signs of dog otitis interna tend to reflect the involvement of these structures:
- Head tilt towards the side of infection
- Loss of balance
- Loss of hearing
- Head shaking
A thorough history and full clinical examination including otoscopy are needed for the diagnosis of otitis interna. Definitive diagnosis of otitis interna may require advanced imaging.
Visualising the tympanic membrane
Knowing whether the tympanic membrane is ruptured or intact is of key importance when managing cases of otitis. If a dog eardrum is ruptured, treatment plans will need to be adjusted accordingly to ensure only topical medications with low ototoxicity are used.
The normal canine tympanic membrane is a thin translucent membrane at the base of the horizontal canal. With a canine ruptured eardrum, the membrane will appear absent, and the middle ear cavity will be visible. With an acutely infected ear, the tympanic membrane can be easy to visualise, however with chronic infections, the canal may be stenotic with lots of debris and discharge making visualisation tricky. Pain associated with ear infections can add to the difficulties involved in a thorough examination.
So, what is the best course of action where it is not possible to visualise the tympanic membrane, or the dog will not tolerate otoscopic examination?
Sedating or anaesthetising the dog will make examination easier and less painful for the patient. Flushing the ear repeatedly with a cleaning product with no ototoxicity is advisable and preparations containing boric acid or zinc can be useful for this. Thorough ear cleaning may help in attempts to visualise the eardrum and will also improve the health of the ear canal, enabling antimicrobials to work more effectively.
Canine otitis media treatment: how to treat a ruptured eardrum in a dog
Treatment for a canine ear infection with a ruptured tympanic membrane can be challenging and a multimodal treatment plan is required for the best chance of success. The multimodal treatment plan should include:
- Topical treatment with ear cleaners with no ototoxicity
- Systemic antibiotics selected based on appropriate culture and sensitivity results. They may need to be continued for 6 to 12 weeks to achieve a clinical cure. Where topical antibiotics are used, care should be taken to avoid ototoxicity.
- Pain relief - otitis media is a very painful condition and appropriate analgesia should always be used.
If the eardrum is still intact, a myringotomy (surgical incision in the eardrum) may be required to aid in diagnosis and treatment.
Treatment protocols for otitis interna are similar to those for otitis media but may it be necessary to continue treatment for longer, up to 4 months in some cases.
So, can a ruptured tympanic membrane heal? A ruptured eardrum in a dog will heal if the underlying disease process that caused the damage is treated. And how long for a dog’s ruptured eardrum to heal? Healing can take several weeks or even months depending on the severity of ear disease.
The earlier in the course of ear disease that treatment is initiated, the greater the chance of success. In almost all cases there will be predisposing factors or primary causes that need to be addressed to avoid recurrence of signs. Many dogs will require lifelong treatment to keep ear disease under control and regular routine ear cleaning with an ear cleaner that is safe for long term use will be a vital part of their management protocol.