Ear Care and Disease

Otitis externa is one of the most frequent reasons for owners to seek veterinarians help. The prevalence of otitis externa in dogs has been reported to be between 10-20 percent, although in more tropical climates it is probably closer to 30-40 percent. Unfortunately, the term otitis does not refer to a specific disease but to an inflammation of the external ear canal. It is a symptom of many diseases and not a specific diagnosis. The actual underlying causes of otitis are numerous. The purpose of this lecture is to review the general principles of ear care and the most important causes of otitis externa. Physiology of the Ear Canal

The ear canal in the dog and cat can be divided into a vertical segment (which is continuous with the pinnae) and a horizontal segment that abuts the tympanic membrane. The canal is almost entirely surrounded by cartilage that offers stability to the structure. Besides the obvious auditory function of the external meatus, the canal also offers protection of the tympanic membrane and the middle ear from direct injury. Preventative Ear Care and Ear Cleaning Preventative ear care begins with a complete history and thorough physical examination. Historical information and physical findings are necessary to identify patients at risk. Specific information about previous and concurrent medical disorders is essential, because ear disease may co-exist with other disease or be secondary to systemic diseases.

Routine cleaning of the ear canal is not necessary and may be contraindicated in the healthy dog and cat. Most dogs do not require cleaning of the ears. Mild to moderate amount of wax is normal. Cerumen has antibacterial properties that help to reduce the over population of bacteria and yeast.

Cleaning, when necessary, should be complete and non-irritating. A mixture of vinegar/water (1/10) is a good degreasing solution to remove wax and dry the excessive moisture in the ear canal. The liquid should be gently applied in the canal, the ear massaged to allow breakage of the cerumen and cotton balls used to remove the cerumen and wipe out the excess of liquid. Extreme care should be used when mechanically cleaning the ears. The use of cotton applicators should be avoided or limited as they may cause rupture of the tympanic membrane. Also powders should not be applied in the canal as they build up predisposing to the development of secondary infections.

Accumulations of cellular debris and exudates indicate the presence of ear disease. Swabs of this material should be collected and the canal should be cleaned. The color, texture and odor of the exudates from a diseased ear can provide clues regarding the underlying primary cause of the otitis and the perpetuating factors that may be involved. Dark brown

Robert Clipsham, DVM, PhDor black, granular, dry (like coffee grounds) exudates characterizes infestations due to ear mites. A moist brown discharge tends to be associated with bacteria (cocci) and yeast infections. Purulent creamy to yellow exudates are most often seen with bacteria such as Pseudomonas. Waxy, greasy, yellow to tan debris is typical of a ceruminous otitis. Thorough cleaning of the ear canals is vitally important for successful management of otitis for several reasons. Examination of the external ear canal and the tympanum cannot be complete until the canal is cleaned. Wax, oil and cellular debris may be irritating, prevent medication from contacting the canal epithelium, and produce a favorable environment for microorganisms to proliferate and inactivate certain antibiotics. Several products are available on the market and they should be used as directed by a veterinarian as some of them may interfere with the efficacy of the topical medications. Also some of them may be irritating if not completely removed thus appropriate flushing by a veterinarian might be required. These products are usually classified as either ceruminolytic or drying agents.

1. Ceruminolytic agents (e.g. Cerumene) emulsify the waxes and lipids to help flush them more readily from the ear canal. They contain surfactants and detergents (e.g. diotyl sodium sulfosuccinate or DSS, squalene, carbamide). In general such products should be applied 5-15 minutes prior to cleaning. General massage improves their effect. Most of these products are contraindicated with ruptured tympanum. However, frequently the condition of the tympanum cannot be determined until after the canal has been cleaned. In those cases the probability of ototoxicity may be decreased by flushing with water after the application of such agents. In a recent study several cerumuminolytic agents were applied in the middle ear and squalene was the only one that did not cause any damage.1 However, it should be realized that there is no completely safe solution for cleaning the middle ear. Even water can cause ototoxicity.

Some disinfectant cleansers, such as chlorhexidine, are contraindicated with ruptured tympanums.

2. Drying agents (e.g. Epi-Otic) are applied after the ear has been cleaned and is relatively dry. Most contain alcohol and one or more of the following: boric acid, benzoic acid and acetic acid. Some products are a combination and they tend to have less drying agents and mildly ceruminolytic than the standard desiccants (e.g. Epiotic, Oticlens). When flushing an ear with a ruptured tympanum the use of saline of 1:1 or 1:3 dilutions of five percent acetic acid (white vinegar) are recommended. The fluid is discarded with every flush and suck cycle and the canal is filled again with clean saline. This is repeated multiple times using a fair amount of saline. The best results for deep ear cleaning or flushing are obtained with the patient under general anesthesia. Cleaning cannot be done on very swollen, stenotic, ulcerated or painful ears. Such cases need to be treated symptomatically initially and cleaned at a later date when the inflammation has been reduced and the canals have opened.

Causes of Otitis Externa

Otitis may have numerous causes and a common classification is to break them down into predisposing, primary and perpetuating. Predisposing factors are those that place a patient

at risk but by themselves are not able to cause otitis externa. Primary causes are usually the actual inciting agent that directly causes otitis externa. Perpetuating factors are those that prevent the resolution of otitis externa once the problem has been established. Predisposition Factors and Risk Assessment

The most successful management requires that these factors are recognized and, whenever possible, controlled. Early detection may prevent unnecessary pain/hearing loss and reduce the prevalence of chronic and refractory disorders. 1. Breed Predisposition and Anatomic Conformation Otitis occurs more frequently in breeds of dogs that have pendulous ears (e.g. Cocker Spaniel) and those with hair growth in the ear canal. Originally this difference was thought to be secondary to variations in the temperature and/or humidity of the ear’s microenvironment in dogs with different ear types, however no difference in temperature was found between ear types. It is becoming more and more evident that variations in the anatomy and the number of glands may predispose certain breeds to otitis externa. Dogs with longhair coats and pendulous ears should have the hair clipped frequently around the auricular orifice and the concave surface of the pinnae. Hair in the ear canal should be removed with a forceps and twisting (rather than plucking, which is more painful) the hairs out by twirling the forceps to improve ventilation in the canal. Great care should be used when removing these hairs as excessive trauma to the area may predispose to an infection. Stenosis of the ear canal (e.g. Shar-Pei) is another variation in the anatomy that can predispose dogs to otitis externa. In Shar-Peis the stenotic canal and the conformation of the pinna that is tightly folded over the external orifice increases the risk of otitis externa. Stenosis of the canal can also be acquired (e.g. abscess, neoplasm). 2. Climatic variations In a recent study monthly variation in ambient temperature, rainfall, and relative humidity correlate positively with increases in the number of first-time otitis externa cases seen. 3. Life Style Dogs used for activities that involve exposure to field are at increased risk of ear disease. Foreign bodies, especially plant material, often become trapped in the canal. These animals should be examined frequently. 4. Maceration of the Ear Canal Any increase in the moisture of the ear canal can lead to maceration. Moisture in the canal, whether introduced by swimming, bathing, or inappropriate treatment may cause otitis externa of inflammation of the external part of the ear canal. A combination of water retention, epidermal maceration, increased ceruminous gland activity and secondary infections may be responsible for disease. Dogs that swim may benefit from prophylactic treatment with a drying agent (e.g. acetic acid). 5. Excessive Ear Cleaning Mechanical trauma of the ear canal through vigorous hair plucking and the use of cotton swabs or other objects to remove wax, as well as the use of irritant topical solutions and excessive cleaning that alters the normal micro-flora, are all factors that predispose to the development of infections.

DISEASES OF THE EAR FLAP aka the “Pinna”

Infections of the Pinna

Bacterial or fungal infections of the pinna (earflap) commonly occur. Scrapes and scratches to the pinna can allow bacteria to invade the skin. Often damage is done when the dog scratches at the ear as ear canal problems are present. This allows natural, resident bacteria (often staphylococcus species) to invade and start an infection. These bacterial infections of the earflap present signs such as local areas of hair loss, small bumps where infection is present (called pustules) and crusts or scabs in areas where the infection is trying to heal itself. Sometimes similar patches of infection are present on other areas of the body. (aka pyoderma).

Fungi can also invade the earflap. Although not very common, superficial fungal dermatitis (ringworm infections) will cause local areas of hair loss, sometimes in a ring or circular pattern and occasionally as crusts on the pinna. As with bacterial infections, lesions on other parts of the body may also be present. Diagnosis of these infections is based on examination, woods light screening, and microscopic examination of plucked hair root samples and/or special cultures. Hair and skin sample preparations should reveal either internal (endothrix) or external (ectothrix) fungal bodies (spores or hyphae) affecting the shafts and root. Ectothrix fungi fluoresce while endothrix do not due to the UV light of the Wood’s lamp not reaching them. Some fungi are only in the skin and must be prepared with a 10-20% potassium hydroxide solution (KOH).

Young pups with poorly developed immunity can have severe, sterile inflammatory disease of the face and ears known as puppy strangles, properly called Juvenile Cellulitis. In these cases, the face, eyes and/or ears are very red, swollen and often discharge oozing pus. The pup may also have a fever and nodes in the neck will swell and sometimes rupture. The cause of this condition is unknown.

TREATMENT OF INFECTIONS OF THE PINNA

Bacterial and fungal infections of the pinna are treated using topical and/or oral antibiotics or antifungal medications, medicated creams and shampoos to disinfect and cleanse the ear. If ear canal disease is present, that too must be treated for any level of success to occur. With severe infections, clipping and scrubbing the area with antiseptic preparations often helps quicken the recovery. Puppies that have Juvenile Cellulitis are frequently treated with prednisolone, antibiotics and astringent topically.

PARASITE INFECTIONS OF THE PINNA

Demodicosis due to demodectic mange will generally show lesions of reddened, localized, circular areas of hair loss, itching (prorates) and crusting of the skin. Lesions on the face and legs are usually present. Sarcoptic Mange will produce a very pruritic (itchy) and (often) crusting dermatitis along the edges of the earflap as well as other areas of the body. This parasite causes such an intense itching that simply rubbing the edge of the pinna will cause the dog to try to scratch with the hind leg. Diagnosis of these parasites is based on physical exam and positive skin scrapings. Demodex mites are easy to diagnose and will be present in large to huge populations. Srcoptes mites are very hard to find and will require dozens of scrapings in some pets and/or surgical biopsy to diagnose them definitively.

Dogs left outside in areas where flies are present, particularly around horses, often suffer from Fly Bite Dermatitis aka “flystrike” when they attack the edge of the pinna. The bites ulcerate the skin, which bleeds, then black crusts will form in the area. The pet may scratch the ears or shake the head to relieve the local irritation. Myiasis is the result of blowfly larvae feeding on living tissue. Repellents may help prevent this problem. Fly control is accomplished by picking up dog wastes and fly traps are crucial for any degree of control. Ear hematomas often result and require expensive surgery when fly control is not practiced. Fly Bite Dermatitis is treated by cleaning the earflap and applying medicated ointments to prevent further damage.

TREATMENT OF PARASITES OF THE PINNA

Treatment for Sarcoptes or Demodex is the same as per these problems generally. Clipping hair from the ears and scrubbing scabs and crusts away with medicated shampoos is very helpful. Antibiotic treatment is also needed if secondary infections have occurred. Local creams are used for small skin spots while whole body baths and dips for several weeks are used for extensive infections. Fortunately, specific spot on medication formulas sold as flea control can be used for both types of mange at two week intervals for most cases. It is not uncommon to treat sarcoptic mange suspects rather than biopsy them to expedite recovery without anesthesia and surgery.

ALOPECIA OF THE PINNA (HAIR LOSS)

Loss of hair from the pinna without inflammation, crusting, or other symptoms is known as Idiopathic Pinnal Alopecia. This most often occurs in male Dachshunds and is considered to be a hereditary disorder similar to human male pattern baldness. Sometimes an endocrine (hormonal) disease may be involved. Miniature Poodles may suffer from a related form of this problem but the hair will usually regrow several months later while the Dachshund may never regrow the hair. Treatment is usually not needed or effectual.

EAR MARGIN SEBORRHEA

Seborrhea is a disorder of keratinization that most often occurs in breeds with pendulous ears such as the Dachshund or the Cocker Spaniel. Seborrhea will usually also affect other parts of the body, as well. However, when the ears are involved, signs including scales, crusts and loss of hair will occur along the margins of the ear, especially near the tip. Itching is uncommon, but the problem may become quite unsightly. Diagnosis is based on clinical signs, skin scrapings and skin biopsy and lack of other causes.

TREATMENT OF EAR MARGIN SEBORRHEA

Rarely is there a cure for Seborrheic diseases, so treatment often centers on controlling the symptoms which includes the buildup of scales, crusts, plugs and excess oil on the ears and other body areas. Medicated shampoos such as Allerseb®, T-lux® or benzoyl- peroxide (Pyoben®) based products among others are very good at cleansing the skin. Antibiotics and cortisone are used in cases where infection and inflammation has become apparent. Retin-A, vitamin A, zinc, essential fatty acid (EFAs) supplements extracted from fish oils and several other drugs may have applications in various forms and secondary problems of the disease that occur.

AURAL HEMATOMA

An aural hematoma is a blood and fluid filled swelling of the pinna. It most often occurs secondary to traumatic head shaking and scratching of the ear from any problem which causes the ear to itch. Some studies indicate that immune-mediated disease may be present causing a spontaneous bleeding between ear layers. The swelling may be localized or encompass the entire area of the flap; diagnosis should include a search for the initiating cause.

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TREATMENT FOR AURAL HEMATOMA

First, an attempt to determine and treat the initiating cause of a hematoma is very important. If a hematoma was secondary to a foxtail in the ear for instance, and that was left untreated, the problem would not be solved. Rarely will a hematoma resolve by itself and if so, the ear is often left grossly deformed. Drainage with a syringe or test tube may produce results if repeated frequently or left in place for long periods of time, but most often, the ear will refill with blood after such treatment. The best recognized therapy is to surgically open the skin of the ear on the inside surface, remove a small flap of tissue, place numerous regular sutures along the line of the incision in some fashion for 3-4 weeks to help encourage smooth healing. The goal is that the layers of skin and cartilage will "weld" together to form a permanent bonding of the pinna tissues. Surgery is usually successful and permanent.

ENVIRONMENTAL DISEASE OF THE PINNA

Sunburn of the earflap is uncommon but can occur in areas of high sun exposure on dogs with white or light colored ears. The earflap will show signs of localized hair loss and redness, followed by crusting and possibly ulceration. Frostbite can occur when the dog is exposed to subzero temperatures for prolonged periods of time. Damaged areas may be whitish or blue and will later slough. This predisposes the patient to skin cancers later. Pale pigmented cats and dogs (esp. boxers and pit bulls) should NOT BE ALLOWED to sun outside for more than a few minutes! Diagnosis is based on the history of exposure and physical examination.

SYSTEMIC ILLNESS AND THE PINNA

Immune-mediated diseases (autoimmune induced), endocrine diseases and allergies can all affect the pinna. Signs may range from redness and itching of the flap, to hair loss, ulceration, severe infection and crusting of the area. Most often other signs of illness are present and treatment of the primary problem will return the pinna to normal. Diagnosis is based on history, physical examination, blood counts, serum chemistry and hormonal analysis as indicated.

DISEASES OF THE EAR CANAL

INFECTIONS OF THE EAR CANAL (OTITIS EXTERNA)

It is important to understand that most infections of the ear canal have some initiating cause; rarely do these infections simply erupt on their own. Bacteria, yeast's and fungi reside in and around the ear canal and under normal circumstances do little more. Parasites, moisture, diseases of the pinna and allergies can all initiate ear canal disease.

The usual signs of ear canal disease are head shaking, scratching the ear, rubbing the face and/or ear, soreness when touched, a sharp fetid odor and possibly some type of exudate or discharge coming from the ear canal. Many people quickly and erroneously conclude that most dogs with these symptoms have ear mites, which is not the usual case. The type, color or consistency of the discharge does not always reveal the cause of the problem. Again, as ear canal problems are often secondary to other disease processes, the dog may be showing signs of skin disease or other problems that must to be taken into account.

Your veterinarian will make a diagnosis by examining the ear, including a deep otoscopic exam and perform cytology or possibly a culture to determine the cause of the problem and the best course of therapy. Often cleaning the ear under sedation may be needed to

reveal the initial cause if deeper ear problems are present. In cases where the ear disease has kept returning after treatment, or fails to respond to therapy, middle or inner ear problems may be present.

Signs of Middle Ear and/or Inner Ear Disease include head shaking, rubbing the face and ear, scratching, discharge and pain. Poor appetite, fever, dry eye, drooling, a head tilt, facial nerve paralysis, trouble walking or balancing and circling to one side or direction may additionally occur. Diagnosis is made by otoscopic exam, which may reveal a ruptured eardrum in many cases. Cultures and X-rays are also important to establish a diagnosis and prepare a treatment plan.

Dogs that have heavy, pendulous ears, such as the Cocker Spaniel, seem to be more prone to ear problems, although the German Shepherd is a notable exception, being a dog with upright ears but also an increased risk for infections. Dogs that swim or live and play in a moist environment are also at increased risk. Dogs that have keratinization disorders or produce excess wax in the ears for any reason will have more trouble with ear canal disease. Breeds such as the Poodle or Schnauzer, which tend to have heavy hair growth in the ears, are also prone to frequent ear infections.

Another problem commonly seen in dogs which have had repeated and/or uncontrolled ear infections is that of sclerosis of the ear canal; a thickening and narrowing of the canal itself. Given enough time, an infection can cause scar tissue to build up. This may become a permanent change and require surgery to reopen the ear so that air may dry the canal and medication to be administered regularly. Dogs like the Shar Pei are often born with a small, twisted ear canal, predisposing even the youngest of puppies to infections.

TREATMENT OF DISEASE OF THE EAR CANAL

While the causes and exacerbating causes of ear canal disease may vary, basic principles of treatment are consistent:

1. Cleanse the ear of any debris and exudates. Wash solutions may be used daily at home in minor cases, while more advanced cases require sedation and flushing of the ear with medicated solutions. Ceruminous otitis is also treated this way as to cleanse the ear of the waxy buildups.

2. Physically remove any foreign objects; again, sedation will most likely be needed. Excess hair should also be removed from the ear.

3. Bacterial infections will be treated with antibiotic drops (or ointments) and oral medication; Yeast infections with antifungal drops and oral medications. Mites will be treated with topical drops and possibly injections of ivermectin. It is also advisable to treat dogs that have ear mites with a flea powder around the ear, neck and rump areas.

PREVENTION AND CONTROL OF EAR CANAL DISEASE

Not only is treatment for ear canal disease important, but as many dogs are prone to recurrent attacks of ear infections, preventative measures are very important. Dog owners can take a few simple steps to control this problem. Three basic principles can be employed:

1. Keep excess hair pulled and clipped from the ear canal to aid air circulation.

2. If your dog gets wet, swims or after a bath apply a few drops of rubbing alcohol to the ears to speed drying and follow a few hours later with a preventative wash.

3. Use a preventative wash solution weekly (or more often) and as advised above to clean debris from the ear and disinfect the internal environment. Avoid the concoctions sold in pet supply stores as these often contain ingredients that can promote or exacerbate ear canal disease.

TREATMENT FOR MIDDLE, INNER AND CHRONIC EAR PROBLEMS

As many chronic infections result in damage and narrowing of the ear canal, treatment and preventative care can become difficult if not impossible. For this reason a Zepp procedure is often performed, which in short, is removal of part of the vertical portion of the ear canal to open the ear for ventilation. It is not always a perfect cure, especially if grossly scared tissue is present. Some ear canals may become so badly damaged and infected as to necessitate complete removal (Alblation) of the ear canal. While such a procedure may sound radical, the alternative to it is often chronic suffering.

Middle and inner ear infections are treated with antibiotic medications, like other ear canal infections and by establishing drainage for exudates produced during the infection. This may necessitate the performance of a Bulla Osteotomy that involves opening part of a bone in the skull where fluids from these types of infections can collect and flushing out the material therein. A drainage tube may be installed. Sometimes, simply rupturing the eardrum and flushing and aspirating the material from this area may be effective. Cultures are very important to determine the type of infection and help insure the best possible chance for cure.

EAR MITES (Otodectes species)

Ear mites are probably the most over diagnosed problem of the ear. Mites cause signs including a buildup of black crusty debris in the ear and intense itching; every time a dog owner notes these symptoms the diagnosis seems automatic. Most commonly, ear canal infections that produce similar exudates are present.

Ear mites are caused by the mite Otodectes cynotis that is common to both the dog and cat, but does not attack humans. The mites burrow and feed within the ear canal, which in itself can cause intense itching, but as time goes on and the mites multiply, infection of

the ear canal and allergic reactions to the mites can occur, compounding the problem all the more so. ((Ear Mite))

The mites can easily move between animals with even minimal contact but cannot live for long without a host. They also lay eggs in the ear canal, which hatch and molt into adult mites about every 19 days. Diagnosis is based on clinical signs and visualization of the mites under the microscope; a procedure called ear cytology.

TREATMENT OF EAR MITES

Mites are easily killed with good quality mite drops, but these will need to be used for about 21 consecutive days. Ivermectin injections have been used with good success with and without the drops. If the ears are full of secondary debris, cleaning or flushing of the ear canals should be performed first. The use of flea powders on the neck and rump of the dog will also hasten the death of these mites.

FOREIGN OBJECTS OF THE EAR CANAL

Foreign body otitis is quite common. Ticks and grass awns, called "foxtails" can easily and quickly make their way deep into the canal. At first, they may simply cause head shaking and itching of the ear, but as these invaders rupture the ear drum and damage the lining to the ear canal, infections generally occur and exudates may hide the object as they accumulate. Pain may also occur, often in proportion to the damage being done by the foreign object. Damage to the pinna and surrounding skin may occur as the dog tries to scratch the ear.

Tumors and polyps that often occur in the ear canal are mentioned here as they most commonly manifest as a foreign object will. Masses in the ear can plug the canal and set up an infection therein. Surgery to open the ear canal and remove the mass may be the only option to stop the infections that then occur.

TREATMENT OF EAR CANAL FOREIGN OBJECTS

Most times, with the help of sedation, the veterinarian will be able to capture and remove foreign objects and then medication will be useful to heal the ear. Plugs and other masses may require some degree of surgery to remove them.

CERUMINOUS OTITIS

Ceruminous Otitis is an increased production and accumulation of waxy debris in the ear canal and can become quite irritating for the dog. Owners often mistake it as a primary ear infection. Yellow oily or waxy material is often seen coming from the ear canal.

Bacteria and yeast in some cases may cause a secondary infection. Many of these dogs have generalized Seborrhea, a disorder of keratinization that most often occurs in breeds with pendulous ears such as the Dachshund or Cocker Spaniel.

Seborrhea will usually affect other parts of the body, but when the ears are involved symptoms include scales, crusts and loss of hair will occur along the margins of the ear, especially near the tip, often with the buildup of the waxy secretions in the ear canal. Itching is common as increased accumulation or secondary infection begins and the problem may become quite unsightly. Diagnosis is based on clinical signs, skin scrapings and skin biopsy. ((Ceruminous Otitis))

TREATMENT OF CERUMINOUS OTITIS

While there is currently no cure for this condition, your veterinarian will have several products available that when used on a regular basis will help dissolve and keep the ear clean of these exudates.

IMMUNE MEDIATED DISEASES

Allergies to airborne irritants, foods or contact with certain objects can lead to inflammation of the ear, as well as other areas of the skin. The earliest clinical signs include redness and itching to the ear canal and the pinna. Sometimes the ear may appear normal, yet be very itchy. Fleas, mites and drugs can also cause these allergic reactions and need to be considered by your veterinarian. Autoimmune disease can also cause eruptions of the earflap and canal and should not be overlooked. Diagnosis is based on history, physical examination, blood tests, skin scraping and skin biopsy in some cases.

DEAFNESS

By definition, deafness is a partial or complete inability to hear. Deafness may occur in one or both ears. Some animals may be born deaf, most times due to genetic defects. These defects are often hereditary so affected dogs and their parents should not be bred.

Other causes of deafness include middle and inner ear disease, foreign objects of the ear canal, ear infections, excessive wax buildup, neoplasia of the ear, trauma to the head or ear(s), poisons and toxins and hypothyroidism. Many older dogs, like many older people, suffer from simple degeneration of the organs of the inner ear which perceive sound. This too produces an often gradual but noticeable loss of hearing in the geriatric dog.

TREATMENT OF DEAFNESS

Dogs with congenital or genetic deafness most often cannot be treated. Dogs with deafness secondary to some other ear disease will often regain most if not all of their hearing once the primary condition is resolved. Age-related hearing loss is usually permanent although adapting human hearing aids to them has helped some patients. In general, most dogs can survive and live happy normal lives with partial or complete hearing loss as long as they are kept away from busy roads and other dangers.

Primary Causes of Otitis Externa

When discussing the primary causes of otitis externa, it is important to remember that the epithelium of the external ear canal is simply an extension of the rest of the skin. Most causes of otitis externa are associated with generalized dermatologic conditions. A complete dermatologic history and work up may therefore be necessary in the diagnosis of many primary otitis externa cases. The most common causes seen in dermatology are atopy (inhalant allergies), food allergy, diseases of keratinization (e.g. primary seborrhea of Cocker Spaniels), and ear mites. It is critical to long-term management of otitis externa that a primary cause can be found.

1. Parasites

The ear mite (e.g. Otodectes) is the most common mite, being responsible for up to 50 percent of the cases of otitis externa in cats; in dogs the incidence is controversial but most authors agree that it is responsible for 5-10 percent of cases. They are most commonly found in the external ear canal, but can survive for some time on the surface of the skin, typically of the head and neck. In the ear the mites are protected by desiccation by a typical dark brown crust. In recurrent cases, it is possible that other in contact animals can act as asymptomatic carriers.

Other mites that can be responsible for otitis include Sarcoptes (mite that causes scabies), Demodex (mite that causes the so-called red mange), Eutrombicula (chiggers) and Otobius (the spinous ear tick of dogs). 2. Micro-organisms

Dermatophytes (which cause “ringwormâ€␣ ) are a relatively common cause of disease of the pinna and in rare occasions may cause otitis externa. Bacteria are most commonly perpetuating factors. 3. Allergies

Allergies are the most common underlying cause for otitis externa in dogs. They include inhalant allergy (also called atopy), food allergy and contact allergy. Inhalant allergy is extremely common in dogs and cats and is the most common underlying cause for recurrent otitis externa in dogs. At least 50 percent of atopic dogs have bilateral otitis externa. In up to five percent of cases, otitis may be the only

complaint. Atopic dogs tend to have itchy feet (e.g. they lick and chew their feet), itchy face (e.g. they rub their face against the carpet or pieces of furniture) and itchy ears. They are predisposed to secondary skin and ear infections that tend to recur after treatment unless the underlying allergy is well controlled. A familial history is present in most cases and strong breed predilection has been reported (e.g.Dalmatians, Terriers, Golden Retrievers). Clinical signs are initially seasonal. Progressive worsening with time is also typical. Diagnosis is based on history, clinical signs, exclusion of other diseases and intradermal skin test.

Food allergy is not as common as the inhalant allergy, but over 20 percent of these cases start with just otitis externa, and ear disease is present in 80 percent of the cases. Food allergy should be considered as a top differential for otitis externa in any young dog (less than one year of age). Food allergy is diagnosed by appropriate food trial (a novel source of protein is selected based on the individual history and used for a minimum of two months).

Contact allergy can result from medications used to treat otitis externa. Whenever a case of otitis externa fails to improve with therapy or worsens after therapy, a contact dermatitis should be suspected. 4. Foreign bodies

Plant material (fox tails), dirt, sand, impacted wax, loose hair and dried medications are frequently responsible for otitis externa. In most cases this is a unilateral otitis. 5. Diseases of keratinization (e.g. primary seborrhea of Cocker Spaniels) Excessive and abnormal composition of cerumen in these cases is responsible for the development of otitis externa and secondary infections of skin and ears. It is usually seen in young animals.

6. Endocrine disorders

Hypothyroidism (decreased production of thyroid hormone) and Cushing’s disease (disease associated with excessive production of steroid hormones) are the most common endocrine diseases that can cause otitis externa. If a middle-aged dog keeps relapsing with otitis externa and is not itchy, then endocrine diseases should be considered as possible underlying causes. 7. Autoimmune disorders Pemphigus (disease in which the organism produces antibodies against component of its own skin) affects the pinna and may extend to the ear canal causing otitis. Lupus (other autoimmune disease in which the organism produces antibodies against various components of the body) can also cause ear disease.

Perpetuating Factors

They include anything that prevents the resolution of an already present otitis externa. Perpetuating factors are a major reason for poor response to therapy regardless of the predisposing factors and the primary cause. In early cases treating the primary cause might be sufficient to resolve the otitis, while in more chronic cases perpetuating factors have to be addressed to resolve the case.

1. Bacteria

In most normal ear canals a variety of bacteria can be cultured. Once predisposing and primary factors cause alterations in the ear canal environment, these bacteria may proliferate and perpetuate an inflammatory reaction. In most cases of chronic otitis

externa bacteria such as Staphylococcus and Pseudomonas are present. Aggressive treatment is warranted as resistance to antibiotic may easily occur, especially in cases when Pseudomonas is cultured. Although bacteria are not a primary cause of otitis, once the infection is established, they can cause significant inflammation and damage. These dogs often present with purulent discharge in the ears. Pain on palpation of the ears is quite common and a strong odor is usually present.

Diagnosis is based on cytology and culture. Initial topical therapy for a case of otitis externa is based on the results obtained from the cytology of the exudates, while in chronic cases is best based on results of culture and sensitivity. Pseudomonas-related infections are extremely frustrating and difficult to treat. Most effective treatments include topical Polimixin B and systemic enrofloxacin or ciprofloxacin. Doses that are used are higher than the ones suggested on the label as resistance occurs rapidly. A commonly used dose for these drugs is eleven mg/kg twice daily. Dogs with OM frequently require two months of systemic antibiotic. As Polimixin B is rapidly inactivated by the exudates, aggressive cleaning is an essential part of therapy. Other topical treatments used for Pseudomonas include acetic acid (vinegar/water 1:1) and silver sulfadiazine (one gram of silver sulfadiazine is mixed with 100 ml of sterile water and 0.5 ml of the mixture is applied twice daily). Also pre-soaking the ear with edetate trisodium (tris-EDTA) 15 minutes prior to application of the antibiotic increases the efficacy. Finally, topical enrofloxcin (Baytril otic) can be used in Pseudomonas infections. In cases where Staphylococcus is the cause of otitis, other antibiotics are usually used including cephalexin (22 mg/kg twice daily) and trimethoprim-sulfa (25 mg/mk twice daily).

2. Yeast

Malassezia is the most common perpetuating yeast that contributes to otitis externa. It is a budding organism with the shape of a peanut and is part of the normal flora (both skin and ears) of dogs and cats. It is a common complication with allergic otitis (80 percent of cases) and may result as a super-infection following antibiotic therapy. Grossly the discharge is thick, dark, and sweet smelling. Diagnosis is usually based on the physical findings and microscopic examination of the exudates (cytology). Topical therapy is usually sufficient and miconazole and clortrimazole (e.g. Conofite, Lotrimin) are the most commonly used ingredients. In rare cases of otitis media due to Malassezia, systemic treatment is necessary and ketoconazole (Nizoral tablets) is used at five mg/kg twice daily for three to four weeks. Side effects include anorexia, vomiting and diarrhea. 3. Progressive pathological changes

Chronic inflammation stimulates the proliferation of the skin lining the ear canal. As a consequence, thickening of the canal occurs leading to stenosis of the canal. More importantly the skin is thrown into numerous folds, which inhibits effective cleaning and the application of medications. These folds act as a site for the perpetuation and protection of secondary microorganisms (e.g. bacteria). Laser surgery has been used successfully to correct excessive stenosis and thickening of the canal.

4. Otitis media

Otitis media (inflammation of the middle ear) results from chronic inflammation of the external part of the ear canal, rupture of the tympanic membrane, and establishment of infection in the middle part of the ear. Exudate in the tympanic cavity is difficult to treat with topical therapy and often remains as a source for infection. Otitis media is usually

bacterial in origin. Clinical signs suggestive of otitis externa include head shyness and pain on palpation of the ears. Some cases of otitis media might present with head tilt, circling and dry eyes, but the vast majority does not have neurological abnormalities. As the tympanic membrane quickly grows back after rupture, otitis media may also be present even if an intact membrane is seen on otoscopic examination. Radiography cannot be used to completely rule out the presence of otitis media since 25 percent of confirmed cases had no radiographic evidence of the disease. In a study otitis media was present in 80 percent of cases of chronic, relapsing otitis externa therefore it must be considered as a possible cause of any refractory or relapsing otitis externa. Treatment of otitis media is based on bacterial culture/sensitivity results. Most cases require long-term antibiotic therapy (minimum of two months) and aggressive topical therapy. Conclusions

Otitis externa is a very common clinical presentation in small animals. A good history is very important in every case of otitis externa to identify predisposing and primary factors. Aggressive treatment is needed in most cases of relapsing otitis externa as an infection of the middle ear might be present.

1 Mansfield PD, et al. The effects of four commercial ceruminolytic agents on the middle ear. JAAHA 97; 33: 479-86.

1Griffin CE, Kwochka KW, MacDonald JM. Current Veterinary Dermatology: the art and science of therapy.Mosby Year Book, St. Louis, 1993