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Comparison of two ear cytological collection techniques in dogs with otitis externa

Choi, Nellie, Edginton, Heather D., Griffin, Craig E., Angus, John C.
Veterinary dermatology 2018 v.29 no.5 pp. 413
Bacilli, Malassezia, bacteria, cotton, dogs, ears, lymphocytes, macrophages, monocytes, otitis externa, rubber, t-test, veterinary medicine, yeasts
BACKGROUND: Canine otitis externa is a common disease. Cytological evaluation of otic exudate is a useful diagnostic test to direct and monitor treatment for otitis externa. One method of collecting ear cytological specimens utilizes a cotton‐tipped swab inserted into the vertical ear canal. A proposed alternative method is to aspirate exudate from the deep horizontal canal using a rubber tube. HYPOTHESIS/OBJECTIVES: To compare cytological findings between two different collection techniques by evaluating the numbers of bacteria, Malassezia yeast and inflammatory cells. ANIMALS: Thirty client‐owned dogs with otitis externa. METHODS AND MATERIALS: A prospective, randomized, blinded comparison study. Ear canals from each dog were sampled using cotton swab and rubber tube. Ear cytological preparations were evaluated independently by two investigators for polymorphonuclear leucocytes (PMN), monocytes/lymphocytes, macrophages, yeast, intracellular (IC) cocci, extracellular (EC) cocci, IC bacilli and EC bacilli. RESULTS: A paired Student's t‐test was used to compare the two techniques. The inter‐investigator reliability for PMN, EC bacilli and yeast was good, and for EC cocci was moderate. There were significantly higher numbers of PMNs obtained by the tube method (P = 0.0024) than by the cotton swab method. There were no statistically significant differences between cotton swab and rubber tube methods for monocytes/lymphocytes (P = 0.7780), macrophages (P = 0.1751), EC cocci (P = 0.1262), EC bacilli (P = 0.1162), yeast (P = 0.5371), IC cocci (P = 0.6606) or IC bacilli (P = 0.6761). The technique was well tolerated. CONCLUSION: An alternative ear cytological collection technique was identified which enables sampling of the deep horizontal canal.