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

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.