Otitis media/interna

Introduction

Cause: bacterial infection of the inner and middle ear.
Signs: peripheral vestibular signs.
Diagnosis: imaging (radiography, ultrasonography, CT scan, MRI).
Treatment: surgery.
Prognosis: guarded.
Otitis media and otitis interna are terms that refer to inflammation of the middle and inner ear, respectively .
Otitis media and otitis interna are commonly referred to one single pathology. While they have a lot in common, there are some differences:
- Otitis media is easier to visualize with diagnostic imaging, but does not produce peripheral vestibular signs.
- Otitis interna more difficult to visualize with diagnostic imaging, but produces peripheral vestibular signs due to labyrinthitis.
- Otitis interna without otitis media may occur.
- Otitis media without otitis interna may be common, as many rabbits with detected changes in the middle ear are asymptomatic.

In rabbits, these conditions are most commonly associated with bacterial infection.
Disease may be unilateral or bilateral, but often bilateral.
Otitis media and otitis interna often occur concurrently; subclinical otitis media may have prevalence of 10-30% in rabbits.
Otitis externa is correlated with otitis media/interna.
Prevalence of CT changes in middle/inner ear in rabbits with vestibular signs is 55%. The rest of rabbits with vestibular disease may be false-negative results, otitis interna without otitis media, encephalitozoonosis or other conditions.
Rabbits that are housed in or originate from large breeding colonies, commercial units or rescue centers that report outbreaks of respiratory disease are thought to be at higher risk.
The association of otitis media/interna with respiratory disease is controversial.

Print off the Owner Factsheet on Ear canker to give to your clients.

Clinical signs vary from none (asymptomatic cases) to severe neurological disturbance depending on the nature and severity of the disease and the anatomic structures involved.
The onset of signs may be acute or chronic/progressive.
Rabbits with otitis media (without otitis interna) may present with non-specific clinical signs, eg lethargy, inappetence, and/or pain or pruritis associated with the base of the ear .
Facial paralysis may occur and can be unilateral or bilateral. Unilateral facial paralysis is more common. Facial paralysis is seen as contraction of the affected side .
Purulent material may be present in the external ear if the tympanic membrane has ruptured or if otitis externa is associated (and maybe the initial cause) with otitis media/interna.
Otitis interna is a common cause of peripheral vestibular disease in rabbits and affected animals usually present with neurological signs, including head tilt Head tilt , rolling, ataxia and/or nystagmus.

Disease incidence does not appear to be related to geographic location.
Countries where lop rabbits are more popular, eg UK, may have increased prevalence.

Lop eared rabbits have a much higher incidence of otitis media secondary to otitis externa .
Lop eared rabbits are predisposed to otitis externa due to the abnormal conformation of the external ear canal and the poor ventilation inside the ear; this can lead secondarily to otitis media/interna.

It can occur at any age.
There are no reported age or sex predispositions associated with otitis media/interna. Due to chronicity and slow progression of otitis media in some cases, clinical disease may be more prevalent in older rabbits.

Variable, but generally moderate to expensive. Definitive diagnosis, particularly if CT or MRI are used, is expensive. Surgical treatment, many times involving both ears in two separate surgical events, is expensive.
Rabbits with clinical disease affecting one ear may be more predisposed to develop the same problem in the other ear.
In early cases with mild clinical signs, empirical treatment is generally inexpensive.
Most cases are chronic in nature by the time of presentation/diagnosis, therefore long courses of medication and frequent revisit appointments may be required.

To prevent traumatic injuries, rabbits with torticollis Head tilt due to otitis interna must be handled carefully, as they tend to roll uncontrollably when stressed.
Surgery is very aggressive and has some associated risks: facial nerve paralysis, lack of improvement or even worsening of clinical signs.