Dog Ear Disease
11 Apr, 2018

If your dog has an infected ear, maybe with yeast or bacteria or ear mites, he is not alone. The most common ear disease, otitis externa, which means inflammation of the external ear canal, is among the most frequent reasons to seek veterinary care. We will discuss this particular set of conditions shortly. Additionally we will briefly describe some other ear disorders, too. If you take away nothing else, understand that otitis externa is a clinical sign rather than a primary disease. It indicates something is a amiss, like an itch or cough or rapid heart rate or a smoky room.

FIRST THE VET EXAM. An otoscope is a handheld magnifying light source used to look inside the ear canal. It, or a video otoscope, is always used unless the ear tissue appears too painful or contaminated or swollen to examine. The doc looks through the scope and notes the condition of the ear, the canal, and if possible, the ear drum. He has already inspected the pinna, or ear flap. He examines both ears, even if only one is affected. A twofer.

WHAT HE/YOU SEE: A diseased external ear canal may look painful, red, moist, swollen, ulcerated, proliferative (reactive tissue growth), narrowed, purulent (pus), waxy, plugged. There might be evidence of self-trauma. It may have a foreign body or mass. It may be occluded. Behavior may include head shaking, scratching, rubbing, vocalizing and resentment to being touched there..

WHAT HE/YOU SMELL: Anywhere from stinky to foul to rank. You get the idea.

ADDITIONAL OBSERVATIONS: Ear disease may be associated with other disorders such as food reactions and allergy, both of which may have additional symptoms. Additionally, 15% of acute and 90% of chronic otitis have associated middle ear disease, even if the ear drum is intact. Thus, dizziness or facial drooping, signs of otitis media, may accompany fido’s appearance.

YEAST. Malassezia pachydermatis is present in nearly half of normal dog ears and in up to 80% of dogs with otitis externa. A third of the middle ears of dogs with Chronic Otitis had yeasties. The decision to treat for yeast infection is based on lab results, history, response to previous therapy, and severity of clinical findings.

BACTERIA. Staphylococcus, Streptococcus, Pseudomonas spp and Coliforms are both normal isolates and are associated with ear disease. (Proteus spp is likely present only in disease.) In cases of chronic or recurrent bacterial otitis externa, the most common problematic opportunistic pathogen is invariably Pseudomonas aeruginosa.

Concurrent external ear and middle ear infection frequently have different bacterial populations with different susceptibility to antibiotics.

PARASITES. Otodectes cynotis is the ear mite most commonly implicated in parasitic otitis. They reside both in the ear canal and elsewhere on the host’s body, and are highly contagious among different species of pet animals. Clinical signs result either from the irritation they produce or allergies to them, and their presence in small numbers does not always create symptoms. Yet, to those who are allergic, as few as three mites can cause clinical signs. In patients with much debris or liquid in the ear canal, they might not even be available for observation, and so the primary cause is therefore missed.

WAX and SCALES.

You may have seen a wax scale after pruning your holly. Florida wax scales are a serious pest of citrus plants throughout the southern US. Moreover, you might market candles and need to weigh your ingredients. None of these observations have anything to do with canine ear diseases. Sorry. However, diseases that cause increased accumulation of wax (cerumen) and greater production of scales (keratinization disorders) may cause a form of otitis externa. They include certain endocrine (hormone) and skin diseases.

ALTERED EPITHELIAL MIGRATORY PATTERNS

And you thought climate change primarily affected the migration of birds and mammals. Disturbances in microclimates effects changes on land at sea and in the ear. (Sorry again). In fact, rather than the normal clearance mechanism of canal epithelium migrating to the outer ear orifice, these cells slough backwards, falling down deep into the central canal, congesting its depths with all kinds of wax and scales and hair and debris which ultimately become caustic and obstructive and allow for infectious overgrowth.

LAB and MICROSCOPIC RESULTS and interpretation. Frequently a pet owner will treat their pet’s affected ear/s without regard to how appropriate the therapy. As a result, the pet often is presented to the vet long after the condition has been established, making the diagnosis and treatment more frustrating for everyone. Additionally, our office is occasionally called asking if we wouldn’t mind dispensing ear medication without an examination. Granted, that is less costly, but only in the short term, unless it is a continuation of recent therapy.

In addition to visual inspection of the vertical and horizontal ear canals and associated structure, and clinical presentation, evaluation of the patient includes cytology. This means gently swabbing the ear canal for material to be examined under the microscope. This tissue harvest is stained, or mixed with mineral oil, and the number and characteristics of bacteria, yeast, white blood cells, and parasites are noted and evaluated. Also, if a bacterial culture is needed, a separate swab is collected for submission.

WHITE BLOOD CELLS (WBC or LEUKOCYTES)

Normal ear canals do not have white blood cells. They are present only as a result of infection, which can be a result of ulceration or exudative inflammation of the epithelial lining of the external canal or, of crucial significance, extension from the tympanic cavity of concurrent otitis media. They are often absent even during the overgrowth of organisms on the epithelial lining of the external canal. Their presence encourages the prescription of systemic antibiotics and monitoring for their disappearance indicates improvement. The rare exception is the immune mediated skin disease called Pemphigus foliaceus (among others) characterized by sterile (ie no bacteria) pustules.

Patients in pain often won’t allow for these procedures to be performed while they are conscious. Thus, general anesthesia is sometimes required. At that time, additional investigation and therapy can be instituted, such as middle ear diagnostics, flushing, imaging, biopsy, foreign body removal.

CAUSES OF OTITIS EXTERNA.

We could classify causes as the underlying condition or primary cause, predisposing causes, perpetuating causes.

PRIMARY causes might include any of a variety of parasites, foreign bodies, allergies, and endocrine diseases and immune diseases. The latter may be especially suspect with a history of UTI or skin infections. These are conditions that directly result in the development of clinical disease.

Note: Adverse immunologic response to otherwise harmless environmental or dietary antigens (atopic dermatitis and food allergies/food intolerance, resp) are important common primary causes of otitis externa. Ignoring their impact is terribly unsound. Ouch.

PREDISPOSING causes might include anatomic conditions like heavy floppy hairy ears, narrow ear canals, space occupying tissue like polyps, moisture from swimming or bathing, irritation from aggressive cleaning technique or medication. These are conditions that make the affected individuals more susceptible to developing disease and have more severe disease when afflicted by primary causes.

PERPETUATING causes would include the various infectious agents that become established when the opportunity presents, either normal inhabitants or additional migrants from the middle ear. These are conditions that once established can maintain worsen or prevent resolution even after theprimary cause has been resolved.

TUMORS, CYSTS, POLYPS, NODULES, GROWTHS.

Both benign and malignant conditions affect the ear canals of dogs and cats. They may present as innocent or hidden inhabitants until fleshed out.

OTITIS MEDIA (Middle Ear Inflammation)

Diagnosis and treatment of OTITIS MEDIA. (Middle Ear Inflammation)

(Note that the ear has disorders associated with its external, middle and internal geography. Internal ear conditions are a topic outside of this discussion.)

As noted way above, 15% of acute otitis externa cases and as many as 50-80% of chronic otitis externa cases have secondary middle ear disease. That’s remarkable and needs to be addressed even if it does not seem clinically apparent. Indeed, an intact ear drum does not rule out otitis media, but only makes the diagnoses more mysterious. The ear drum in dogs, less so in cats, is often difficult to see, and if the ear canal is narrowed, it might be impossible. Any externa case inadequately treated will damage the ear drum, weakening it and thus allowing invasion to occur more readily.

Cats: can be by extension of infection through the Eustachian tube or as a result of a polyp through the ear drum. It might be associated with viral upper respiratory infection, as well as Mycoplasma and Bordetella, which are difficult to isolate. Bacterial infection often incites accumulation of pus and liquid exudates. Poor kitty.

Dogs: usually there is a history of recurrent or chronic otitis externa. When a patient with a ruptured ear drum and otitis media is examined, lots of fluid discharge will be seen in the external ear canal. It’s useful to point out that mucus is not produced in the external ear canal, but is discharged from the tympanic bulla of the middle ear. Thus, the observation of mucus says that without question the ear drum is busted. There might be so much that it’s all over the side and top of the patient’s head. Additionally, a patient with otitis externa for 6-8weeks can be assumed to have otitis media.

Pain may cause head shaking, reluctance to chew, and resentment to palpation of the base of the ear. If the facial nerve is damaged, eye dryness or lip/ear/face droop may be noticed, as well as a consequent drool. Hearing may be deficient. Drainage through the Eustachian tube may interfere with breathing. Oral exam concentrating on the back of the mouth might reveal this.

As long as there is infection, the hole in the ear drum will not heal. With controlled but not completed therapy, the drum will repeat its contribution to sustaining the condition by leaking secretions. In fact, it may completely heal while trapping the source of the next outbreak beyond anyone’s ability to know.

When otitis media is suspected, examination of the ear drum (tympanic membrane or TM) is mandated. It’s done under gas anesthesia with a breathing tube because drainage through the auditory tube into the nasopharynx can be dangerous.

The TM may have a variety of appearances. It may be intact or ruptured. While normal is pearly and translucent, abnormal can be grey and opaque. Fluid may produce a bulge, while pus may be seen as yellow. If ruptured it may look like a deep dark hole.

One way to determine patency of the TM is to instill warmed saline with diluted fluorescein dye into the anesthetized patient’s affected ear. If if comes out the nose or into the throat, bingo.

Sometimes it’s necessary to puncture the drum in an anesthetized patient. The procedure is called a myringotomy. It’s done to relieve pressure or to collect cellular debris for examination or to growth a bacterial culture. It’s done following disinfecting and drying
False Middle Ear: External pressure on the ear drum from abnormal canal tissue coupled with reduced auditory tube function, pulls the ear drum into the middle ear. This hollow finger fills with debris making even calls for tasty treats hard to hear.

OTOTOXICITY. An incompetent eardrum allows fluids to seep into the middle ear. The cause of its reduced function is often the caustic nature of inflamed external ear secretions. Adding to the severity, many drugs administered into the ear but also including those ingested and by injection, damage the structures and thus function of the middle and inner ear. Deafness, dizziness, and difficulty in equilibrium ensue. Only some antibiotics, several antifungals, certain cortisone medications, and few cleaning agents can be used safely.

EAR SURGERY

Medical treatment is not guaranteed to work. Sometimes, unfortunately, surgery is required in End-Stage Otitis. Surgical Techniques include Lateral Ear Canal Resection (LECR), Vertical Ear Canal Ablation (VECA), Total Ear Canal Ablation (TECA) + Lateral Bulla Osteotomy (LBO). Significant hearing loss is a predictable accompaniment of TECA/LBO. At this stage of the disease, CT or MRI is often suggested. The most common reason for complications is failure to identify and treat the primary cause of the disease. Recovery can be complicated if inflammation, proliferation of tissue and dystrophic calcification entrap the facial nerve running near the juncture of the external canal and the tympanic cavity. Incomplete removal of secretory epithelium may create a fistula. Chronicity and severity can disrupt the architecture of the middle ear so that surgical landmarks are difficult to identify and the risk of surgery is heightened. Of course infection is always a potential visitor. These operations are onerous and complicated and not for the weak of heart or wallet. Nuff said.