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Abstract

Necrotizing Sweet’s syndrome is a rare and severe variant of acute febrile neutrophilic dermatosis characterized by a necrotizing pattern of sterile inflammation involving the epidermis, dermis, subcutaneous fat, fascia, and occasionally muscle, closely mimicking potentially lethal soft tissue infections such as necrotizing fasciitis. We report the case of a previously healthy 45-year-old woman who presented with acute onset fever, headache, and a rapidly progressive, erythematous, indurated plaque on the left posterior knee. Initial differential diagnoses included erythema migrans, rickettsial pox, necrotizing soft tissue infection, pyoderma gangrenosum, and Sweet’s syndrome. Skin biopsy demonstrated diffuse keratinocyte necrosis with subjacent papillary dermal edema sufficient to separate the epidermis from the dermis, a dense interstitial neutrophilic infiltrate extending into the subcutis, and prominent angiocentric cuffs of monocytes and lymphocytes admixed with neutrophils. Vasculitic changes included mural fibrin deposition, luminal thrombi, and extravasated fibrin and red cells. Neutrophilic eccrine hidradenitis was striking, with monocytes and neutrophils permeating eccrine ducts and coils. Areas of dermal neutrophilic dermolysis and adipocyte membrane disruption were also present. Special stains (GMS, PAS, Gram) and type I interferon (MXA) immunostaining were negative for microbial pathogens. In the setting of negative microbiologic studies, abrupt febrile onset, and characteristic histopathology, necrotizing Sweet’s syndrome was favored over infectious or other neutrophilic dermatoses. Prompt recognition of this entity is essential, as it is exquisitely corticosteroid-responsive and may deteriorate with surgical debridement, underscoring the need to include it in the differential diagnosis of rapidly progressive necrotic skin lesions to prevent unnecessary morbidity.