Disease of the outer portion of the ear canal (otitis externa) is one of the most frequent presenting problems seen, day to day, in first opinion veterinary practice. Representing inflammation of the cells that line the outer ear canal, otitis externa (OE) can be painful, recurrent and at times, frustrating to treat.

Occasionally, surgery is needed to address complicating components of the disease. In this discussion topic, we address the underlying factors of the disease and explain why dispensing medication or a cleaner (as may be requested) without examining the patient, offers suboptimal care.

So, what exactly is otitis externa (OE)?

As mentioned above, OE is inflammation of the skin (epithelial) cells lining the external ear canal. The ear canal extends all the way down to the eardrum. This inflammation narrows the ear canal and if severe, can prevent sound from reaching the eardrum. Inflammation also encourages increased production of ear wax (cerumen) and impairs normal upwards epithelial cell migration. With such changes, the normal processes of self-cleaning within the ear canal become less efficient.

OE is a complex disease which involves primary initiating factors but also many different predisposing and perpetuating components. Failure to treat any of these factors can lead to severe and progressive disease. Repeated and recurrent disease episodes can lead to potentially permanent and irreversible pathological changes within the ear canal. Long standing cases may also become resistant to medical treatment.

What are the symptoms of an ear infection?

Head shaking or scratching at the ears is commonly seen in affected animals. The skin of the earflap and the entrance to the ear canal, maybe red, sore and inflamed. An associated smell or malodour may also be detected. Your dog may yelp when you touch their head or lift their ears. Occasionally the dog may hold an ear/one side of the head, in a lowered position.

So, what are the “precipitating factors” for OE?

Dogs that suffer from OE usually have an underlying cause or disease. 

However, the primary causes of inflammation are those which produce the initial inflammation in the ear. The most common of these is an allergic skin disease. Such allergic skin may be a consequence of both environmental allergies, food allergies, or both. Ear disease may be the only symptom seen. In some cases, widespread body skin irritation, inflammation and itchiness maybe also noted. Certain breeds are over-represented as being more prone to allergic disease. For more information please, take a look at our blogs on inherited allergic disease; skin “infections”, yeasts, and food allergies.

Ear mites (Otodectes) also will cause ear irritation. Puppies may be predisposed.

In the Summer months, foreign bodies such as grass seeds may become trapped within the external ear canal. Such a case would manifest acutely, with an abrupt onset of ear discomfort.

In an older patient, hormonal problems (which alter the health of the immune system), are also possible causes of recurrent disease. Such diseases include an underactive thyroid gland (hypothyroidism) or a steroid excess (hyperadrenocorticism / “Cushings disease”).

Many middle ear diseases (otitis media) and tumours within the ear canal, are also possible precipitating causes.

Whilst bacteria and yeast infections are often found in OE, they are rarely the primary or initiating course of ear disease. Rather, living as harmless skin organisms, they will just readily take advantage of an altered and inflamed ear canal environment (caused by other factors). Typically, Staphylococci bacteria and Malassezia yeast are involved; these are secondary causes of inflammation. They contribute to the inflammation, itch and discomfort of ear disease, whatever has caused it, so do need addressing in the treatment plan. 

And what predisposes a dog to otitis externa?

Predisposing causes do not cause primary disease but make OE more likely to persist in the face of treatment. They include hairy ears that affect certain breeds (such as spaniels) and which increases the humidity of the ears. Dogs with heavy ear flaps will also suffer with reduced airflow over the entrance to their ear canals. Again, decreasing ventilation and increasing humidity within the ear canal. Narrowed ear canals (through either natural conformation or due to repeated or ongoing ear disease) also increase the risk, as does frequent swimming. 

And what are the perpetuating factors?

Perpetuating factors are those which arise due to a change in the local environment of the ear, resulting in continued disease. They may include accumulation of discharge (wax and pus in the ear canal, providing a suitable “home” for bacteria and yeasts) and swelling of the ear canal lining. These factors may also prevent healing of the ear disease and as such, must be identified, addressed, and treated as part of any successful management plan. 

So, what is the best advice for my dog with itchy ears?

Whilst it may seem frustrating, anticipating that “just some more ear drops” will be prescribed by your vet, it is vitally important that whenever possible if ear symptoms are seen, every dog is examined on every occasion. This will allow your Vet to establish the underlying precipitating and predisposing factors that are contributing to the disease. Nowhere is this more important than when the ear disease keeps coming back. 

It is usually wise that an otoscopic examination (looking down the ear with a specialised instrument called an otoscope), is performed in every case. OE can be a difficult and frequently painful condition to treat – however, treatment must be thorough and appropriate, otherwise permanent damage can occur. A ruptured eardrum and extension of the disease to the middle ear are possible serious complications. Follow on tests and investigations are likely to be needed, and ongoing management may well be required in many cases. 

There is also of course, the possibility that different diseases and factors contribute to symptoms on different occasions. For example, a juvenile dog that obtained a grass seed foreign body once, may go onto develop allergic disease as a young adult, and/or hormonal issues as a middle to older aged patient. So just because a treatment worked once, it does not necessarily follow that it will be effective a second time.

In addition to addressing underlying causes, your Vet may recommend regular ear cleaning at home. This has a variety of benefits including the breakdown and removal of excess wax and microbes (those bacteria and yeasts we previously discussed), whilst returning the ear canal environment to a normal balance. It also allows better action of topical medications since the surface cells are more readily exposed to topical medication.

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