A pilot study to develop an objective clinical score for canine otitis externa

Background - The lack of an accepted clinical scoring system in canine otitis externa makes it difficult to compare clinical trials.
Hypothesis/objectives - To develop a score that is clinically relevant, reliable, and sensitive to change.
Animals – Client owned healthy dogs (n=55) and dogs with otitis externa (n=60).
Methods - We compared 0-3 and 0-5 assessments of erythema, oedema/swelling, erosion/ulceration, exudate and pain of the ear canals to a reference 0-2 scale. Additional data included odour, pruritus scores, tympanic membrane condition, treatment outcome, and neutrophil, bacterial and Malassezia counts.
Results - There were no significant differences between the vertical and horizontal canal scores (correlation coefficients >0.93). Correlation coefficients for the 0-3 and 0-5 scales were also >0.9 for all parameters, but the 0-2 scale was more variable. Pain and pruritus did not correlate well with the lesion scores, and were associated with suppurative and erythroceruminous otitis respectively. Neutrophil and microbial counts were variable and could not be used to generate cut-off values to differentiate healthy and affected ears or determine the response to therapy. Total scores ≥4 differentiated affected from healthy ears with 91.1% sensitivity and 100% specificity, and scores ≤3 were 100% sensitive and 91.9% specific for clinical success. The intra- and inter-observer reliability was high (intraclass correlation coefficients >0.95 and Cohen’s kappa coefficients >0.65).
Conclusions and clinical importance – This pilot study showed that the 0-3 Otitis Index Score (OTIS3) for erythema, oedema/swelling, erosion/ulceration and exudate is suitable for further validation by a larger group of clinicians.