Abstract

Loxoscelism produces a spectrum of cutaneous and systemic manifestations driven by sphingomyelinase D, the principal dermonecrotic toxin. The resulting necrotic lesion is often clinically indistinguishable at initial presentation from several severe infectious conditions, most notably necrotizing skin and soft tissue infections (NSTIs), community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections with necrotizing features, and ecthyma gangrenosum. Diagnostic errors carry consequences in both directions: necrotizing fasciitis misdiagnosed as a spider bite may delay life-saving surgical intervention, whereas loxoscelism managed as a bacterial infection exposes patients to unnecessary antimicrobial therapy and may delay appropriate supportive care. An additional layer of complexity arises from secondary bacterial superinfection of Loxosceles wounds, a genuine complication that requires targeted therapy but appears to be substantially less common than current prescribing practices suggest. This narrative review examines the pathophysiological mechanisms underlying the shared clinical phenotype of these conditions, describes the clinical and laboratory features that facilitate meaningful bedside differentiation, and proposes a practical framework for clinicians evaluating an acute necrotic wound of uncertain etiology. Particular emphasis is placed on the recognition of NSTIs as surgical emergencies that should never be excluded solely on the basis of ancillary investigations.