Dog with painful crusting skin rash after antibiotic treatment

Abstract

A 5‐month‐old female Brittany spaniel was presented with peracute crusting dermatitis. The dog had been treated with cephalexin for cystitis 6 weeks earlier. Systemic signs included hyperthermia, anorexia and dehydration. Dermatological signs were characterized by crusted and exudative lesions over the face, trunk and limbs. These lesions were very painful. Clipping revealed arciform and annular patterns. The periphery of these target lesions remained indurated and ulcerated. Histopathological features of lesional skin biopsies revealed a hydropic interface dermatitis with prominent single‐cell apoptosis of keratinocytes at all levels of the epidermis and satellitosis of lymphocytes. Similar lesions were observed within the infundibular region of hair follicle outer root sheath epithelium. PCR tests (parvovirus, herpesvirus) performed from lesional biopsies were negative. Clinical and histopathological cutaneous lesions were compatible with erythema multiforme. Drug implication criteria showed the possible role of cephalexin. Symptomatic treatment (cleansing, antiseptic bathing, rehydration, antibiotics, morphine patch) was prescribed. Twenty‐four hours later, the skin was particularly painful. A pustular dermatitis was observed over the entire body. These pustules were large and contained a yellowish material. Cytology revealed nondegenerative neutrophils and acidophilic acantholytic keratinocytes. Histopathological findings included subcorneal pustules containing nondegenerative neutrophils, acantholytic keratinocytes and few eosinophils. Clinical and histopathological cutaneous lesions were compatible with pemphigus foliaceus. Prednisolone (1 mg/kg twice daily, orally), antiseptic bathings and antibiotics (marbofloxacin) were prescribed for 3 weeks. Clinical improvement was then observed. The dose of prednisolone was tapered to an alternate‐day regimen over 2 months. Cutaneous lesions completely disappeared. No relapse was observed for 4 years. The clinical succession, erythema multiforme and then pemphigus foliaceus associated with a cutaneous adverse drug reaction, is the main interest of this case. Funding: Self‐funded.