Otitis Externa

Otitis externa is an inflammation of the external ear canal. The ear canal begins at the outside opening of the ear and extends inwards to the eardrum. Causes include bacteria, yeast, fungi, ear mites, accumulation of wax, thick or matted hair in the ear canal, debris, impaired drainage of the ear, and infections from elsewhere in the body. Ear infections are even affected by the weather, with more happening in humid conditions. The most common underlying cause of otitis that we see are allergies that are potentiated by yeast.

The ears of dogs (especially those with pendulous ears) and cats are ideal for the growth of bacteria and yeast because they are moist and warm, and contain wax and other debris. The funnel shape of the ear canal effectively traps debris, further complicating treatment of infections.

There may be underlying causes of repeated ear problems. These include allergies, hormone imbalances, narrow ear canals, growths and polyps within the ear and resistant bacteria. Sometimes further testing or surgery is needed to treat some of these problems.

Diagnosis of the Cause

We will often take a swab of the ear canal to look at under the microscope during the consultation. We will roll this out on a microscope slide, stain it with special stains and then heat fix it before looking at it at 10 to 1000x magnification. We will usually see little dots (Staphylococcus), rods (Gram negative bacteria) or purple “snowmen” (Malazzesia - yeast). This tells us which ear medication we should be using. Some cases of ear infection with gram negative rods will require us to send a sample to an external laboratory so they can grow the bacteria and find out what antibiotics they are susceptible to.

Many cases of otitis require sedation or an anaesthetic in order to clean the ear and look down the bottom of the ear canal.

Important Points in Treatment

  • General Anaesthesia is often necessary to allow thorough cleansing of the ear canal and to obtain specimens for bacterial culture.
  • The longer the infection has been present, the more difficult it is to clear up. In severe longstanding infections, surgery may help to control the problem.

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