Ulcerative dermatitis and vasculitis due to cutaneous Pseudomonas aeruginosa infection following grooming
Dominique Comeau, Hailey Bertrand-Sluman
Animal Health Laboratory, University of Guelph, Guelph, ON (Comeau); Parkside Animal Hospital, North Bay, ON (Bertrand-Sluman)
AHL Newsletter 2023;27(2):28.
Skin biopsies from an 8-year-old female spayed Labrador retriever crossbred dog were submitted to the Animal Health Laboratory to investigate extensive ulcerative and erosive lesions in the skin over the dorsum, sides, and lateral hindlimbs (Fig. 1). The dog had initially presented with a fever of unknown origin two days prior to the acute development of the skin ulcers. All other workup performed, including bloodwork, radiographs, urinalysis, and ultrasound were within normal limits. The dog was shaved to allow the skin lesions to be fully cleaned, injectable antibiotics and steroids were administered, and she was started on prednisone.
On histologic examination of skin biopsies, there was extensive ulceration of the skin surface which was often covered in a thick crust of fibrin, neutrophils, and cellular debris (Fig. 2). There was marked inflammation of the underlying dermis, and occasionally, there was separation of the remaining epidermis from the dermis. Within the dermal inflammation, there was targeting of the small superficial blood vessels by neutrophils, with destruction of some of the vessel walls (Fig. 3). The vessel walls contained neutrophils which were often degenerating, consistent with leukocytoclastic vasculitis. The intact epidermis distant from the ulcers was histologically unremarkable, making immune-mediated conditions such as toxic epidermal necrolysis / erythema multiforme or bullous pemphigoid less likely. Primary cutaneous vasculitis was considered, however, this would typically involve the deeper larger blood vessels rather than the small superficial vessels noted in this case.
Overall, the skin lesions histologically resembled a burn with secondary hypersensitivity or infection-induced vasculitis. This was suggestive of a severe bacterial infection with a staphylococcal-type bacterium, resulting in a condition known as “staphylococcal scalded skin syndrome”. This syndrome occurs due to the production and secretion of toxins by the bacteria, leading to sloughing of the superficial layers of skin.
A swab of the lesions was submitted for bacterial culture and had abundant growth of Pseudomonas aeruginosa in pure culture. This bacterium is common in wet or aquatic environments, and is a common cause of skin infections following swimming or bathing. It can produce toxins similar to those produced by Staphylococcus spp., leading to a lesion which is indistinguishable from scalded skin syndrome. Pseudomonas aeruginosa can be found in water and is also a contaminant in opened shampoos and bath products. Additional history revealed this dog had been bathed with a deshedding shampoo a few days prior to development of the lesions.
This dog was continued on a combination of immunosuppressive and antimicrobial therapy. The lesions resolved over several weeks (Fig. 4). AHL
The assistance of Dr. Robert Foster (Ontario Veterinary College) in the examination and workup of this case is gratefully acknowledged.
Figure 1. Extensive ulcerative skin lesions at the time of initial presentation. Inset: closer view of the skin ulcers.
Figure 2. Overview of a sample of the skin with extensive ulceration of the surface, covered by a thick crust.
Figure 3. Neutrophilic inflammation of the dermis, centered on small blood vessels.
Figure 4. Skin lesions resolving approximately 20 days after submission of biopsy samples.