Evaluating Otitis Externa

Otitis externa is among the most common skin diseases of dogs. In this study, investigators compared 2 methods for evaluating histologic changes in the external ear canal. Normal ear tissue (n = 53 ears) was harvested from cadaver dogs, and affected tissue was harvested from dogs undergoing surgery for end-stage ear disease (n = 20 ears). Tissue was routinely processed and stained with hematoxylin and eosin.

For subjective scoring, the entire ear specimen was examined; the dermis,epidermis, and appendages were considered. For objective scoring, photomicrographs were taken of 3 randomly selected fields with a 10× objective lens. A free software program called ImageJ was used to measure the thickness of the epidermis, dermis, and area and diameter of the lumen of ceruminous and sebaceous glands. Subjective and ImageJ measurements correlated for epidermal hyperplasia, ceruminous gland dilation, and hyperplasia and tissue inflammation.

This article described a new use for ImageJ, an image-processing program used extensively in research. Clinicians do not generally obtain biopsies to evaluate otitis severity or treatment response but to evaluate patients based on subjective evaluation of gross changes. The primary value in using ImageJ for otitis evaluation would be in clinical treatment trials. Most otitis evaluation is done through subjective means. Although subjective measurements showed good correlation to severity of ear disease, objective measurement offers additional benefits such as allowing for independent review. Validating an objective otitis measurement tool will hopefully raise the bar in clinical trials and result in more rigorous product evaluation.—William Oldenhoff, DVM, DACVD