Inner ear disease

All our small pets share a very similar ear anatomy made up of three main sections – the outer ear, middle ear and inner ear. The outer ear comprises all the visible parts of the ear and the ear canal up to, but not including, the eardrum. The middle ear includes the eardrum and the space beyond it that houses three small ear bones known as the ossicles. The inner ear is made up of the cochlea, the auditory nerve and the vestibular, or balance system. The middle and inner ear are very closely associated and will often be affected by disease at the same time. Inner ear disease is sometimes called Otitis interna or labyrinthitis.

All vertebrates have this ear physiology so all are at risk of inner ear disease. In the case of rodents, this will include mice, rats, guinea pigs, hamsters, gerbils, chinchillas and degus.

The most common cause of inner ear disease is an infection, which often starts as a respiratory infection before tracking up the Eustachian tube connecting the back of the nose and the middle ear. Other disorders in this area can include benign growths known as polyps, tumours or trauma such as a skull fracture.

Often the first signs of inner ear disease are due to disturbances in the vestibular system and include a head tilt, loss of balance and falling or rolling to one side. Other symptoms may include scratching at the affected ear, facial nerve paralysis meaning they are unable to blink on the affected side and signs of just generally being unwell such as lethargy and going off food.

Most cases of inner ear disease will be diagnosed based on appropriate clinical signs and a relevant history. Sometimes signs of middle ear disease (and therefore presumed inner ear disease) such as a bulging eardrum can be seen on otoscopic examination, but because rodents are so small, this is not always possible. Confirmation would require taking an x-ray of the skull and looking for changes in the tympanic bulla (the part of the skull that contains the middle ear).

Because inner ear disease is most often caused by an infection, antibiotics will usually be the first choice of treatment. Anti-inflammatories and painkillers can sometimes be useful too. If the cause is thought to be physical such as a polyp or a tumour, treatment is often symptomatic as surgery in rodents in this area is incredibly risky and complex. Aside from antibiotics and anti-inflammatories, in other species anti-nausea drugs can be used as the disturbance to the balance system is thought to cause a vertigo-like feeling, but these are not documented in rodents, and so would not routinely be prescribed.

In many cases, if the cause is treatable such as an infection, and that treatment is started promptly, then often it will result in a cessation of the disease. However, as with many conditions that involve the neurological system, some symptoms such as facial paralysis or a head tilt may be permanent. If mild, most animals can live like this quite happily but if the symptoms don’t resolve and are more severe or if the animal doesn’t respond to treatment and their quality of life is negatively affected, then euthanasia should be considered.

It is impossible to completely prevent the risk of developing an inner ear infection but as prompt treatment gives the best chance of a resolution, being on the lookout for suspicious signs is vital. Any respiratory symptoms should also be assessed by a vet and treated appropriately if infection is suspected, minimising the chances of the infection spreading.