Stuart Fitzgerald
Dr Stuart Fitzgerald (MVB MANZCVS, University College Dublin)
 
Closeup of a vet cleaning a dog's ear

Problems affecting the ears are very common in dogs, and though some are relatively simple to resolve, others can be extremely troublesome, and may require lifelong management.

Failure to control chronic ear disorders can lead to scarring and narrowing of the ear canals, further predisposing to future problems. In this article, I will discuss the symptoms, causes, and treatment of a range of ear disorders commonly seen by owners and veterinary surgeons.

Anatomy of the Ear

Dog ear anatomy

Dogs have incredibly sensitive hearing, being able to pick up on sounds of a far lower intensity and higher frequency than we humans. Eighteen different muscles attach to the ears, giving our pets the ability to rotate and lift their ears to follow and locate sounds with astonishing accuracy.

As well as being highly sensitive to sound, a dog’s ears are also sensitive to pain, having a rich supply of nerves innervating their lining. The ears are comprised of the outer ear flap, which is properly called the pinna. The shape and position of the pinna varies widely between the breeds, from being small and upright in the Cairn Terrier to the rounded, dropped ear seen in the English Springer Spaniel.

The pinna helps funnel sounds into the ear canal, which is a tubular structure made of cartilage, and consists of two parts: the vertical canal, which runs from the entrance inside the pinna directly downwards, and the horizontal canal, which it meets at close to a right angle. The horizontal canal then runs directly inwards, towards the skull, where it meets the tympanum, a thin membrane more commonly known as the ear drum. The tympanum separates the outer ear from the middle ear. The middle ear is a bony chamber, containing the nerves and associated structures responsible for sensing motion and sound. The portion responsible for motion detection is called the vestibular apparatus.

Signs of Ear Problems

Dog shaking head

Being a sensitive organ, the earliest signs of trouble within the ear are usually a manifestation of pain and discomfort. Dogs will scratch and paw at the affected ear, or may shake their head vigorously and repeatedly in an attempt to dislodge the unseen irritant. Others prefer to rub the side of their face against an abrasive surface, such as a carpet. If the pain is severe, the dog will resent having the ear handled, and may yelp or attempt to bite anyone that lifts the pinna or touches the side of their head.

With many of the problems we commonly see, the ear may produce pus or excess amounts of wax, this being another defence mechanism used to flush foreign materials from the ear canal. The canal and the underside of the pinna may be appreciably wet, or a foul smell may be noticeable. In severe cases, blood may be seen to ooze from the canal. Inflammatory problems of this nature affecting primarily the ear canal are termed otitis externa.

Should an ear disorder become a chronic problem, it may extend into the middle ear. This may or may not involve rupture of the ear drum, but is likely to result in severe pain. In addition, the inflammation will often cause dysfunction of the vestibular apparatus involved in maintaining balance. Dogs with middle ear disease, or 'otitis media', may exhibit a tilted head carriage or characteristic, rhythmic to-and-fro movements of their eyes, similar those seen in a child that has spun rapidly in circles.

Breed Predispositions

Certain unfortunate pedigree breeds are known to be predisposed to otitis externa. In some cases, this is due to either the conformation of the ear or a tendency to excess production of wax. As an example of the former, the Shar Pei has very small, folded ears, which tend to sit quite tight to the entrance to the ear canal. This arrangement impedes aeration of the canal, providing a warm, moist environment that can facilitate bacterial and fungal overgrowth.

Spaniels and Labrador Retrievers are examples of breeds producing large amounts of wax. This may be an adaptation to their working origins, providing protection from seeds and other materials lodging in the ear, or aiding in expelling water after a swim. However, in some dogs it can also provide a medium for the growth of yeast, and removal of excess wax on a regular basis can help manage otitis in some of these dogs.

Significantly, some breeds are predisposed to skin allergies. These allergies are the major cause of chronic ear disease, and will be discussed below.

Parasites

Many dogs with a sudden onset of ear irritation are found to have parasites within the ear canal. These ear mites, of the species Otodectes cyanotis, resemble microscopic blue-tinged spiders, and spend their lives foraging in the ears of dogs and cats, feeding on cells and debris. The adult mites lay their eggs within the wall of the ear canal, and the presence of both adults and eggs causes intense irritation in some dogs.

In contrast, other dogs appear far less bothered by these creatures, and it is not uncommon in my clinic to see two dogs form one household, one of whom is experiencing extreme pain and distress, while the other gives no indication of the mites’ presence whatsoever. As a response to the mites, infested ears produce copious amounts of dark brown or black wax, and usually have a dry and scaly surface to the skin of the ear.

Eliminating the mites requires treatment of all in-contact animals. In the scenario above, treating only the painful dog is a waste of time and money, as the mites are extremely contagious and will re-infest the treated dog within weeks. It is equally important to remember that Otodectes will also parasitise cats, and so all cats within the household also need to be treated at the same time.

Allergy

Vet inspects dog's ear

A large proportion of dogs with ear infections have acquired the problem as a result of an underlying skin allergy. Studies have shown that as many as 90% of dogs presenting to a veterinary clinic with bilateral otitis externa will eventually be proven to be sensitive to one or more allergens.

In my experience, the majority of the remaining 10% will have bilateral ear mite infestation when they are examined with an otoscope (the instrument for looking down the ear canal). Unfortunately, arriving at a diagnosis of allergy relies on a process of excluding other conditions, which proves costly and is frustrating for many owners.

Determining the Cause of the Allergy

When first examined, these dogs are likely to have active bacterial or yeast infections (discussed below), and so often improve with an initial course of treatment. However, this improvement is likely to be short-lived. Careful examination, submission of microbiology samples to an external laboratory, and microscopic evaluation of ear swabs are the initial steps in the work-up, possibly eventually followed by blood or intradermal tests to identify allergens. A food trial is also necessary, a step that involves exclusively feeding a hypoallergenic diet for a period of 2 months in order to assess the dog’s response.

Food Allergies

Of the potential sources of allergens, food is the easiest to deal with, and dogs with food allergy can be managed largely by feeding the correct diet, though dietary indiscretions are inevitable, and occasional medical treatment may be warranted. Dogs with allergies to environmental agents (e.g. pollens) are more difficult to manage. However, recent advances in the treatment of allergy mean that a range of effective medications are now available, albeit at considerable cost, particularly for larger dogs.

Holistic Approaches to Allergies

Far from relying only on medication in these cases, most veterinary surgeons will try other measures in a holistic approach to the treatment of otitis externa. Omega-3 oil supplements, for example, can be effective in some dogs, as omega-3 is metabolised to produce anti-inflammatory substances within the skin. Regular ear cleaning with a suitable antiseptic preparation will help to reduce the number of microbes in the ear, and prevent secondary infections. In some cases, immunologic vaccinations can be produced to desensitise the patient to allergens identified during testing.

The key to successful management of chronic otitis externa is to appreciate and acknowledge that it is a long-term disorder, and that, rather than striving for a cure, you and your veterinarian are attempting to establish a sustainable programme of management to keep the problem at bay.

Bacterial Infections

Bacterial infections occur in almost every case of otitis, whether the underlying primary cause is allergy, mite infestation, or foreign body. Once inflamed, the skin of the ear canal becomes porous, oozing fluids in which bacteria thrive, and allowing microbes to invade the canal’s surface. In most cases, the bacteria involved are commensals, which means they normally live within the healthy ear canal without causing problems. When the normal environment of the canal is disturbed, the number of bacteria swells, and an active infection is established.

Of more concern are the truly pathogenic bacteria, often of faecal origin, that can cause bacterial otitis. E.coli, Proteus mirabilis, and Enterococci are those most commonly encountered, along with Pseudomonas aeruginosa, which is often found in stagnant water. These bacteria are capable of causing severe otitis without any assistance from an underlying disorder, and result in a foul smell and the production of copious amounts of pus. The reason these bacteria pose a difficulty is that they are capable of rapidly and effectively developing antibiotic resistance, a difficult situation can arise in veterinary practice in which a patient has an active and problematic ear infection that is resistant to all available medications.

When presented with a dog with otitis externa, veterinarians must always take a swabbed sample from the affected ear(s) to allow laboratory sensitivity testing. This procedure will identify the most suitable antibiotic to use for that particular infection, accelerating the dog’s recovery, and preventing the development of resistance.

Fungal Infections

Fungal organisms cause problems within ears in much the same way as the commensal bacteria above, normally living within the canal in small numbers, but proliferating when the ear’s micro-environment is disturbed. The type most commonly involved is Malassezia pachydermatis, which is the source of the strong “canker” smell sometimes picked up from very waxy ears. Malassezia can be managed with ear washes, wipes, or systemic medications, but yeast infection is generally an indication of some other underlying primary ear problem.

Foreign Bodies

Occasionally, foreign material, such as grass seeds and other plant matter, can find their way into the ear canal. Dogs with otic foreign bodies are usually extremely distressed and painful, and will paw and scratch at their ears frantically, while being very reluctant to have the ear examined. While some of these foreign bodies can be dislodged by these efforts, many need to be removed at the veterinary surgery under sedation or anaesthesia.

Management of Ear Disorders

Vet gives a dog ear drops after careful inspection

The most appropriate treatment of an ear disorder clearly depends on its cause. However, a number of points hold true for all of these problems. First, it is vital that owners never put home remedies into their dog’s ear without veterinary guidance. I have seen all sorts of strange concoctions used over the years, though olive oil and cider vinegar remain the most popular. Many dogs with signs of otitis will have perforated ear drums, and anything poured into the outer ear can therefore make its way into the sensitive tissues of the middle ear.

In the same way, veterinary products, such as antibiotic, antifungal, steroid, and cleaning preparations should not be used in an inflamed ear without the express advice of your vet. Almost all of these products have the potential, as do the home remedies previously mentioned, to cause sudden and total deafness should they leak into the middle ear. The most common cause of deafness in younger dogs is this inappropriate use of prescription medications. Less commonly, certain antibiotic preparations can cause systemic toxicity and severe kidney disease if used inappropriately. Should your pet be prescribed a course of topical treatment for a bout of otitis, the remaining product should be discarded at the end of the treatment course to prevent these problems arising.

Dog Breeds