Associations Between Otic Cytological Findings and Clinical Severity by Pathogen Group in Canine Otitis Externa: A Retrospective Study of 318 Cases.

Bacterial burden and neutrophil presence, not Malassezia load, best predict clinical severity in canine otitis externa.

This retrospective study of 318 client-owned dogs evaluated the relationship between otic cytological findings and clinical severity in canine otitis externa (OE), stratified by pathogen group. Clinical severity was objectively measured using the Otitis Index Score 3 (OTIS3, range 0–12), while cytological burden for cocci, rods, and Malassezia was graded on a semiquantitative 0–3 scale; neutrophil presence was also recorded. A moderate but statistically significant correlation was identified between total cytological score and OTIS3 (Spearman's r = 0.45, p < 0.0001). When analyzed by pathogen group, higher cocci and rod scores were significantly associated with greater clinical severity (Kruskal-Wallis, p < 0.0001), whereas Malassezia burden did not demonstrate a significant association with OTIS3. Neutrophil presence was independently associated with higher OTIS3 scores, suggesting a role as a marker of more severe or suppurative disease. Interestingly, the clinical impact of cytological findings varied depending on the predominant pathogen group, underscoring the importance of pathogen-specific interpretation. These findings reinforce the value of combining structured cytological evaluation with a validated clinical scoring tool such as OTIS3 for comprehensive assessment and longitudinal monitoring of canine OE. Clinicians should place particular emphasis on bacterial burden and neutrophil presence when estimating disease severity, while recognizing that Malassezia burden alone may not reliably predict clinical severity in this population.

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