The feline hearing apparatus, when functioning properly, is amazingly effective. While the upper end of the human auditory range is typically between 16 and 20 kilohertz, a cat’s ears can capture acoustical signals up to 60 kilohertz from the environment. Due to a variety of congenital or acquired conditions, however, a lot can go wrong with a cat’s ears, with deafness among the potential consequences. Among all acquired feline ear conditions, the most commonly diagnosed by far is otitis externa, an infection of the outer ear canal that can lead to an overproduction of earwax, progressive tissue damage, and, if untreated, permanent deafness in an afflicted cat.

The most common cause of otitis externa and its frequently adverse consequences is the ear mite (Otodectes cynotis), a tiny, spiderlike parasite that can flourish within the feline ear. Although these parasites, says William Miller Jr., VMD, a professor of dermatology at Cornell University’s College of Veterinary Medicine, are “only about the size of a pinhead,” it is possible to see their minuscule, rapidly moving bodies with the naked eye. The mites are also detectable by the unpleasant mess they make inside an infected animal’s ear canal—a thick, dark, foul-smelling accumulation of wax and debris in which they thrive.

Another organism that can precipitate otitis externa, Dr. Miller points out, is a one-celled fungus, or yeast, known as Malassezia. “All feline ears have Malassezia in them,” he says. “It’s part of the natural flora. But if something changes the climate in the ear, the organisms begin to grow and become too numerous. And you end up with infection.”

If otitis externa is not appropriately treated, the infection can migrate to the middle ear, where it is termed otitis media, and to the inner ear (otitis interna). In the most severe cases, the inner ear can be irreparably damaged, resulting in partial or total loss of hearing. Also, since the inner ear contains the sensory structures that govern a cat’s equilibrium, an affected cat’s sense of balance may be compromised. Otitis externa is most commonly diagnosed in certain breeds—Himalayans, for example—that are more susceptible than other breeds to skin ailments.

Diagnosis of the condition will usually entail a review of an afflicted animal’s medical history and a thorough physical examination, with special attention given to the affected ear or ears. For this, the veterinarian is likely to use an otoscope, an instrument that provides a magnified view of the ear’s inner depths. This device will reveal the extent to which an ear canal is swollen or blocked and whether the ear drum is intact or damaged.

“If you don’t identify the cause and deal with it appropriately,” says Dr. Miller, “the infection may clear up temporarily but will come right back after treatment is stopped.” Treatment of otitis externa is usually a fairly simple matter, he notes, involving the use of antibiotics or antifungal medications. In some cases, however, medical management may be unsuccessful, and aggressive surgery may be required to remove all inflammatory material from affected areas. Unfortunately, the surgery may entail the removal of essential components of the ear’s anatomy, and—although successfully curing a deeply rooted infection—is likely to cause permanent deafness in an affected cat’s ear.