Multifocal papular deep bacterial pyoderma in a Boxer dog caused by Pseudomonas aeruginosa

A young adult Boxer dog was presented with a papular dermatitis on the dorsal back and ventral neck that had developed while it was being treated with cyclosporine and cephalexin for atopic dermatitis and secondary superficial staphylococcal pyoderma, respectively. Histopathology demonstrated nodular to diffuse pyogranulomatous dermatitis with focal furunculosis. Numerous bacterial rods, free in the tissue and engulfed by neutrophils and macrophages, could be demonstrated on stained samples (haematoxylin-eosin; Giemsa). Bacterial culture from an aseptically collected skin biopsy punch sample yielded a pure growth of Pseudomonas aeruginosa, sensitive to a variety of antimicrobials. Successful treatment was accomplished following discontinuation of cyclosporine and an extended course of enrofloxacin. There has not been a recurrence of the pseudomonal pyoderma during the subsequent 2 years.