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Otitis Interna


What structures form the inner ear of dogs and cats?

 

The inner ear of both dogs and cats is similar in structure and function to the inner ear of other mammals, including humans. It is responsible for detecting sounds and maintaining balance.


The inner ear of a dog or cat is composed of two main parts: the cochlea and the vestibular system.


The cochlea is a spiral-shaped structure that is responsible for converting sound waves into electrical signals that can be interpreted by the brain. The cochlea contains specialized hair cells that vibrate in response to sound and send signals to the auditory nerve.


The vestibular system, on the other hand, is responsible for maintaining balance and detecting changes in head position. It contains three semicircular canals that are perpendicular to each other, each containing fluid and hair cells. When the head moves, the fluid inside the canals moves and stimulates the hair cells, sending signals to the brain that help the animal maintain balance.



Overall, the inner ear of dogs and cats is highly specialized and essential for their ability to hear and maintain balance. Any damage to the inner ear can result in hearing loss and balance disorders.

The inner hair cells are the actual sensory receptors, and 95 of the fibres of the auditory nerve that project to the brain arise from this subpopulation. The terminations on the outer hair cells are almost all from efferent axons that arise from cells in the brain.

What causes otitis interna?

 

Dogs and cats can develop otitis interna, an infection of the inner ear. The delicate inner ear tissues become inflamed and infected in this illness, typically as a result of bacterial or yeast overgrowth. The main contributors to this include bacteria from the Staphylococcus spp., Streptococcus spp., Clostridium welchii, and (notably) Pseudomonas aeruginosa. Most of the implicated yeasts are Malassezia. Iatrogenically, head trauma or the use of ototoxic substances when irrigating the middle ear might cause otitis interna due to high pressure from overzealous irrigation. Otitis interna can develop idiopathically as a result of the hematogenous spread of infectious diseases, possibly viral ones.


The German Shepherd Dog, English Springer Spaniel, dogs with pendulous or hairy ears, and dogs with widespread skin disorders are examples of breeds that are predisposed to otitis externa.



Otitis interna is typically brought on by the unilateral spread of otitis media through the round cochlear window to the inner ear, which can damage the facial nerve and sympathetic trunk to the eye, resulting in facial paralysis and either partial or complete Horner's syndrome on the affected side. The cochlea and semicircular canals then cease to function, resulting in unilateral deafness and balance problems.


What are the Clinical Signs of Otitis Interna?

 

Symptoms of otitis interna can include head shaking, scratching at the ear, loss of balance (staggering towards the affected side), dizziness, and hearing loss. If left untreated, this condition can lead to severe complications, such as permanent hearing damage or facial nerve paralysis (Unilateral facial paralysis, involving the upper and lower face).


Other signs include the following:-

  1. Head tilt (affected side down), circling (circling towards the affected side) and nystagmus (fast component away from the affected side - vestibular syndrome).

  2. Concurrent long-term otitis externa.

  3. Concurrent otitis media

  4. The recent treatment of otitis by instilling potentially ototoxic agents into the ear.

  5. Recent bulla irrigation or bulla osteotomy.

  6. Vomiting.

  7. Head trauma.

  8. Seizures.

  9. Sudden onset.

  10. When held up vertically, the body hangs straight down.

  11. General dullness and inappetence

  12. Rolling and falling towards the affected side.

  13. Partial or complete Horner's syndrome: miosis (small pupil), slight ptosis (drooping upper eyelid), enophthalmos (sunken eye), protrusion of third eyelid, conjunctival flare.


How is Otitis Interna Diagnosed?

 

Diagnosis of otitis interna in dogs and cats typically involves the following steps:

  1. Medical history and physical examination: The veterinarian will ask about the animal's symptoms and medical history and perform a thorough physical examination to look for signs of infection or inflammation in the ear.

  2. Examination under anaesthesia: Eardrum rupture identified by palpation with a blunt needle or probe Otitis media and if the Eustachian tube is not patent then there is a high chance of Otitis media.

  3. Otoscopic/Auroscopic examination: The veterinarian will use an otoscope, a special tool for examining the ear, to look inside the ear canal for signs of redness, swelling, discharge, and any foreign bodies. Auroscopic examination is important to rule out Otitis externa, ruptured eardrum and the presence of purulent aural discharge.

  4. Sampling and culture: The veterinarian may take a sample of discharge from the ear and send it for a bacterial culture to identify the type of bacteria causing the infection. Bacteriology and sensitivity of aural discharge usually reveal a mixed infection, including yeasts, susceptible to broad-spectrum antibiotics or polypharmaceutical preparations.

  5. Radiographs: In some cases, the veterinarian may recommend radiographs (X-rays) to get a better view of the middle and inner ear and check for any underlying structural abnormalities, to diagnose chronic otitis media, absence of normal air shadow in tympanic bulla, diffuse thickening of bulla wall, bony destruction and gross bony proliferative changes in the bulla or gross bony proliferative changes with involvement of the temporomandibular joint.

  6. Blood tests: Blood tests may be performed to check for underlying conditions such as diabetes or a weakened immune system that could contribute to the development of otitis interna.

  7. Caloric stimulation: When otitis interna is present, no nystagmus is initiated by irrigating the external ear canal with warm or cold water.

  8. Full neurological examination: Findings of central vestibular involvement include:-

    1. Abnormal function of cranial nerve V (trigeminal) - sensory to face;

    2. Cranial nerve VI (abducens) - eye position is downward strabismus (squint);

    3. Cranial nerve IX (glossopharyngeal) - gag response;

    4. Cranial nerve X (vagus) - vocal capacity;

    5. Cranial nerve XII (hypoglossal) - lingual function.

    6. Deficits in hopping and placing responses.

    7. When held up, the dog's body turned towards the side of the lesion.

    8. Unilateral hypermetria.

    9. History of recent onset of seizures.

  9. Other tests: Other tests, such as CT scans or MRIs, may be recommended in some cases to get a more detailed view of the middle and inner ear.

The veterinarian may use one or more of these diagnostic tools to diagnose otitis interna and determine the most appropriate treatment plan.


Treatment

 

Treatment for otitis interna typically involves the use of antibiotics (broad-spectrum, bacteriocidal antibiotics) or antifungal medications, as well as pain management (oral corticosteroids) and supportive care. In some cases, surgery (bulla or vestibular osteotomy with bulla irrigation if there is evidence of otitis media, marked tissue changes in tympanic bulla, granulation tissue or bony proliferation) may be required to remove debris or address underlying structural issues that are contributing to the infection. If you suspect your pet may have otitis interna, it is important to seek veterinary care as soon as possible to ensure prompt and effective treatment.


How is Otitis Interna Prevented?

 
  1. Prevention of otitis interna is done through thorough diagnosis and treatment of otitis externa and otitis media.

  2. Polypharmacy ear cleaners can also be used in dogs and cats to prevent otitis interna. Polypharmacy ear cleaners are products used to clean and maintain healthy ears in pets, such as dogs and cats. These cleaners often contain a combination of ingredients, including surfactants, emollients, and antiseptics, to help remove dirt, debris, and excess wax from the ears. Some polypharmacy ear cleaners may also include ingredients to soothe and moisturize the skin in the ear canal, as well as ingredients to help combat bacteria and yeast, which can cause infections. It's important to note that while these cleaners can be effective in maintaining healthy ears, they should only be used as directed and under the supervision of a veterinarian, especially if your pet has any existing ear problems.


References

 

Garosi L S et al (2001) Results of magnetic resonance imaging in dogs with vestibular disorders - 85 cases (1996-1999). JAVMA 218 (3), 385-391 PubMed.


Dvir E et al (2000) Magnetic resonance imaging of otitis media in a dog. Vet Radiol 41 (1), 46-49 PubMed.


Rosychuk R A Wet al(2000)diseases of the ear.In: Textbook of Veterinary Internal Medicine.5th edn. Eds: S J Ettinger & E C Feldman. Philadelphia: W B Saunders. pp 986-1002.


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