Extensive fatal Pyoderma gangrenosum in a dog after drug exposure

A 4-year-old, spayed female mixed breed dog was presented with large crater-like, well-demarcated, erosive and ulcerative necrotic lesions of the skin, elevated body temperature and lethargy, that began 14 days after vaccination and treatment with fluralaner and milbemycin/praziquantel. Cytology revealed severe pyogranulomatous inflammation with moderate numbers of extracellular microorganisms. Histopathologic examination showed severe multifocal pyogranulomatous dermatitis and panniculitis with severe dermal edema and severe neutrophilic exocytosis with band-like infiltration of the lower portion of the epidermis consistent with pyoderma gangrenosum. Despite intensive immunosuppressive and antimicrobial therapy and intensive inpatient care, the dog was euthanized 16 days after admission due to complications with clinical signs of sepsis, acute dyspnea and thoracic effusion.