Page 1537 - Clinical Small Animal Internal Medicine

167 Otitis 1475

Table 167.2 Cytologic findings and interpretation
VetBooks.ir Finding Normal ear Abnormal ear

Cerumen Low numbers of Larger numbers of anucleate and nucleated corneocytes
anucleate corneocytes
Malassezia Low numbers adherent Peanut‐shaped organisms >5–10/high power field (hpf) considered significant
to corneocytes
Bacteria Low numbers adherent Large cocci in pairs, fours or clumps usually Staphylococci spp. Smaller cocci
to corneocytes in chains usually Streptococci spp.
Rods cannot be differentiated from each other and may be Proteus spp.,
Escherichia coli or Pseudomonas spp.
Inflammatory cells Absent Neutrophils only in acute disease, neutrophils and macrophages in chronic
disease. Neutrophils are seen in all bacterial skin infections, neoplasia, and
irritant and allergic dermatitis
Acantholytic cells Absent Seen in autoimmune disease (e.g., pemphigus foliaceus)
Neoplastic cells Absent Uncommon. Some neoplasms may shed cells into cerumen; fine needle
aspirates are more useful
Ectoparasites – Otodectes Absent Eggs, immature stages, and adults can be found in cerumen
cynotis, Demodex spp.

0.15%), rotenone (0.12%), piperonyl butoxide (1.5%),
milbemycin oxime (0.1%), and thiabendazole (4%). All
products have activity against Otodectes cynotis. In addi-
tion, ivermectin and milbemycin applied topically would
be expected to have some activity against Demodex spp.
Products with generalized effects such as topical
selamectin and moxidectin may also be used to treat ear
mites. Finally, excellent results have been reported for
orally and topically administered, long-acting, systemic
parasiticides of the isoxazoline class for the treatment of
O. cynotis and demodicosis in dogs and cats.
Antibiotic therapy may initially be based on cytology.
However, where rods or mixed infection are seen on
cytology or where cocci are identified and the case has
not responded to previous therapy, culture and suscepti-
bility should be performed. Antibiotics can be consid-
Figure 167.6 Ear cytology stained with Diff‐Quik showing
numerous rod‐shaped bacteria consistent with Pseudomonas ered as first, second or third line for topical therapy of
spp. intermixed with cocci. otitis externa and indeed for otitis media (Table 167.4).
Glucocorticoids are useful in the therapy of otitis externa.
EDTA‐tris, lactic acid, salicylic acid, isopropyl alcohol, They reduce swelling, pruritus, inflammation, and glandu-
parachlorometaxylenol (PCMX), and microbial adhesion‐ lar secretions. They can also help to open up the ear canal
blocking carbohydrates. EDTA‐tris has been shown to to allow adequate penetration of topical drugs. They may
have antibacterial potentiating activity and will render bac- be given systemically or topically (Table 167.5).
teria more sensitive to topical antibiotic therapy with ami- The more potent topical steroids, such as mometasone
noglycosides or fluoroquinolones when the ear is presoaked furoate and hydrocortisone aceponate, produce more
with this product 10 minutes before antibiotic application. marked antiinflammatory effects than dexamethasone
The cleaning solution should be used to flood the ear canal or betamethasone, which are both more potent than
and then gently massaged to dissolve debris before an prednisolone.
absorbent pad is used to remove excess material. Antiyeast drugs are rarely needed systemically. The
Antiparasitic agents are found in many different azole antifungals miconazole, clotrimazole, and posacon-
ear preparations. Active ingredients with antiparasitic azole as well as nystatin are available in a range of licensed
actions include ivermectin (0.01%), pyrethrins (0.05– veterinary ear drops in the United States and Europe.