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Chronic pathological changes
The ear canals should be carefully examined to determine the severity of pathology changes. Healthy ears should be pain-free, pliable and freely mobile with pale pink, smooth and thin skin.
Otoscopic examination
Most dogs accept this conscious. Clean the ears or use anti-inflammatory treatment to open stenosed ears if necessary. Use sedation or anaesthesia in fractious or animals or painful cases.
Otoscopy can identify foreign bodies, Otodectes, Otobius ticks, inflammation, ulceration, stenosis, the condition
of the tympanic membrane, exudation and chronic changes. Healthy ear canals have a thin, smooth, pale pink lining with a little waxy pale yellow-brown cerumen. The tympanic membrane should be thin, translucent, sloping ventrally and slightly concave.
Acute inflammation results in moist erythematous swelling. Chronic changes have a firm indurated surface. Ceruminous hyperplasia results in a ‘cobblestone’ appearance, which later develops into single or multiple polyp-like growths. The tympanic membrane may be torn, inflamed, discoloured, thickened and/or convex. Its integrity can be assessed by gently probing with a soft tube. Debris can mimic the membrane, but tubes pass into the middle ear without resistance. If the membrane is not visible, use anatomical cues (e.g. the hairs at the ventral insertion of the tympanic membrane) to check that you are at the right level.
Video otoscopy
Video otoscopes have many advantages. The magnification, illumination and image quality allow assessment of fine detail. The working channels facilitate ear flushing, foreign body or polyp removal, minor surgery, laser procedures and myringotomy. Image and video capture improves client communication and helps with follow up of cases.
Nature of the discharge
The dried material at the ear opening can be misleading; always look at material from the ear canals.
Cytology
Cytology samples should be taken from the external ear canals and middle ear as the results may differ. Debris can be collected using cotton buds, catheters, spatulas, curettes or loops. It can be mixed into liquid paraffin to
An Urban Experience
look for mites. Adhesive tape can be used to collect material from the pinna.
Diff-Quik® or Rapi-Diff® type stains are quick and easy, although heat fixing may be necessary with waxy or oily samples. The one-stain method can be very effective for staining microorganisms in thick and greasy smears (put one drop of the basophilic stain on the sample and place a cover-slip).
Large cocci in pairs or clusters suggest Staphylococcus, whereas Streptococcus and Enterococcus are smaller and form chains. Long narrow rods are typical of Pseudomonas, while Proteus and other Gram-negatives are shorter or bipolar. Peanut-shaped yeasts are characteristic of Malassezia.
Staphylococci and Malassezia often form overgrowths without neutrophils. Degenerate neutrophils with intracellular bacteria are usually seen with Pseudomonas and occasionally other infections. Neutrophils are also seen in contact reactions and with ulceration. Mucoid slime is evident with biofilm forming organisms.
It is possible to obtain material for indirect impression smears or fine needle aspirates from lesions or the middle ear in the ear canals or middle ear using fine swabs, curettes or long needles passed through an otoscope. This is best done using the working channel of a video otoscope.
Bacterial culture and antibiotic sensitivity
This is not always required. Microorganisms are easily identified on cytology; Malassezia and staphylococci have predictable sensitivity, but Gram-negative rods (especially Pseudomonas) are frequently antibiotic resistant. However, antibiotic sensitivity data does
not predict the response to topical therapy as local concentrations are ~1-4,000x those used in sensitivity tests. The response to treatment is best assessed by clinical signs and cytology, but any ear not responding to treatment as expected should be cultured. Material should be taken from the ear canals and middle ear if necessary.
Diagnostic imaging
Diagnostic imaging is primarily used to investigate otitis media, but it can also be helpful in chronic otitis externa. It’s possible to perform this using sedation but anesthesia facilitates positioning.
In dorso-ventral or ventro-dorsal views the ear canals should be visible and air-filled. Soft-tissue filling indicates occlusion with debris or stenosis. Mineralisation of the ear canals may be seen in severe cases. Diluted soluble contrast material (e.g. 50% Hypaque® diluted 1:10 in saline) can be used to delineate the canals and test the tympanic membrane – if it is ruptured contrast leaks into the middle ear. However, the fluid may not leak through
 Colour
  Dark brown
  Pale brown to grey
    Pale brown to yellow
   Yellow to green
   Dark green to black
  Consis- tency
  Waxy and adherent
Waxy to seborrhoeic
  Sebor- rhoeic to purulent
 Purulent
 Thick and slimy
 Association
 Cerumi- nous otitis
  Malassezia
    Staphylo- cocci
   Pseudomo- nas
   Biofilm
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