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Hearing and Vestibular Problems in Cats

By Dr. Lana Kuenzi - Kuenzi Family Pet Hospital, Waukesha, WI


Dr. LanaWe immediately associate ears with a sense of hearing; however, ears also can help to maintain an animal’s balance and coordination. Anatomically, the ear can be divided into three distinct units: external, middle, and inner ear.

External Ear:
The pinna (ear flap) is a thin, fleshy funnel-shaped structure that captures sound waves, up to 60 kilohertz, and redirects the sounds down the ear canal. The ear canal is the channel that links the outside environment to the intricate auditory system within the cat’s skull.

The cat’s external ear is extremely mobile due to the numerous muscles attached at the base of the external ear. This ear mobility allows the cat to capture sounds in virtually every direction.

Middle Ear:
The middle ear begins with the tympanic membrane (eardrum). This translucent and taut membrane vibrates from the sound waves hitting it and transmits the vibrations to the three auditory ossicles (small bones). The ossicles transmit the vibrations to the inner ear.

The Eustachian tube connects the middle ear cavity to the back of the throat. This connection equalizes air pressure on both sides of the eardrum.

Inner Ear: The vibrations are transferred from the middle ear to the fluid-filled cochlea, which contains the actual organ for hearing (organ of Corti). This organ transforms vibrations into nerve impulses, which are carried by the auditory nerve to the brain for interpretation.

The inner ear also contains three semicircular fluid-filled canals and two chambers (utricle and saccule) that aid in the cat’s balance and coordination. Sensitive nerves are located within the membranous lining of the structures, and provide information to the brain relative to movement of the cat’s head and position to gravity.

Warning Signs
Your cat could become hearing impaired and uncoordinated if you ignore the signs that signal existing ear problems. Typical warning signs include:

  • Pain or resentment when ears are touched
  • Persistent scratching of the ear which can lead to further trauma
  • Constant twitching of the ears and headshaking
  • Encrusted exudate on ears' surface which may be accompanied by an unpleasant odor
  • Swollen appearance
  • Head tilting, circling, rolling, or stumbling

Common Ear Problems

Exposure
If exposed to harsh outside weather conditions, the outer ear can be damaged. White cats are predisposed to sunburn. Also, excessive exposure to sunlight can lead to squamous cell carcinoma. However, you can provide protection by applying a sun block lotion to exposed ear tips.

The earflap is an easy target for biting insects, such as mosquitoes and gnats. The pesky insects can be deterred from biting your cat’s ears by applying a small amount of an insect repellent to the tips of the ears.

Inflammation
Otitis is the term used to describe an inflammation of the ear that can occur in the outer ear (externa), middle ear (media), or inner ear (interna).

Fifty to 84 percent of otitis externa in cats can be attributed to ear mites (Otodectes cynotis). A higher percentage of ear mite infestations occurs in young cats and kittens. Ear mites live on the ear canal surface and the irritation they cause stimulates the ceruminous glands to produce more wax (cerumen), which they continue to feed upon. Chronic (long-term) ear mite infestations can initiate thickening of the ear lining. Treatment for ear mites may take a minimum of three weeks to ensure that all life stages of the mites have been eliminated.

The dark, moist and warm environment of the ear canal provides the perfect location for yeast, fungal, and bacterial infections to grow and flourish. If these infections are left unchecked, they will become progressively worse and eventually infect parts of the inner ear. Also, the scarring and thickening of ear canal tissues will cause a loss of hearing. Fortunately, these types of infections can usually be prevented by routine ear checks. If infections do occur, your veterinarian will prescribe the proper medication to rid your cat of the microorganisms causing the problem. However, the medication is of little use unless you follow your veterinarian’s instructions on administering the medication.

Middle ear infections are usually the result of untreated external ear infections. These infections are much more painful to the cat. If left untreated, the ear drum may become perforated and result in a loss of hearing, cause facial paralysis by interfering with facial nerve function, or cause Horner’s Syndrome.

Horner’s Syndrome occurs when certain neurons of the nervous system are disrupted from trauma to the upper spinal cord or to the soft tissues in the neck, or middle-ear inflammation. The signs include constriction of the pupil, protrusion of the nictitating membrane (third eyelid), sinking in the of the eyeball, and drooping of the upper eyelid. Prognosis is variable, depending on the cause.

Untreated middle ear infections can progress into the inner ear. Besides the loss of hearing, the cat can have a loss of balance and coordination. Inner ear infections can be potentially fatal by leading into meningitis and brain abscesses.

Polyps
Polyps are fleshy, noncancerous growths that protrude from the mucous membrane lining the middle ear or Eustachian tube, and often protrude into the ear canal or back of the throat. Chronic ear mite infestations or chronic infections may predispose a cat to polyps. Surgery is required to remove the fleshy growths.

Idiopathic Vestibular Syndrome

This is a common disease in adult cats of any age. In the Northeast the incidence is higher in the summer and early fall. The syndrome affects the peripheral nervous system and parts of the inner ear that control balance. Mildly affected cats show only a slight head tilt, while severely affected cats will lie down and roll. The cause is unknown; however, it is hypothesized that it may be caused from environmental factors. Spontaneous recovery occurs within two to three weeks. Your veterinarian may recommend supportive care such as cage rest and administering antiemetics and cortisone. Fortunately, permanent neurologic damage rarely occurs.

Summary

Hearing helps the cat make sense of its environment. Fortunately, most ear problems can be prevented with routine ear care and cleaning. If you have doubts about your cat’s hearing ability, make an appointment with a veterinarian to have the problem diagnosed and treated.