Brown recluse spider bite


  • Brown violin shape on cephalothorax (fiddleback)
  • In Southern midwestern US
  • Loxosceles family


  • Venom contains variety of cytotoxic enzymes, principally Hyaluronidase and Sphingomyelinase-D, which cause a necrotic wound
    • Hyaluronidase: facilitates the penetration of the venom into tissue but does not induce lesion development
    • Sphingomyelinase-D: causes necrosis and lesion formation by initiating the release of pro-inflammatory mediators (thromboxanes, leukotrienes, prostaglandins, and neutrophils)

Clinical Features

  • Bite is initially painless
  • Mild reaction (most common)
    • Mild erythematous lesion that later becomes firm and heals without scar
  • Severe reaction
    • Begins with mild-severe pain several hours after bite accompanied by erythema and swelling
    • Hemorrhagic blister then forms surrounded by vasoconstriction-induced blanched skin
    • By day 3 or 4, hemorrhagic area may become ecchymotic
      • Leads to "red, white, and blue" sign (erythema, blanching, ecchymosis)
    • By end of first week, ecchymotic area may become necrotic with eschar formation
  • Systemic effects (rare)
    • Occur predominantly in children 24-72hr after the bite
    • Nausea/vomiting
    • Fever, arthralgia
    • DIC
    • Rhabdo
    • Renal failure

Differential Diagnosis

Envenomations, bites and stings


  • Definitive diagnosis is achieved only when the biting spider is positively identified
  • Labs
    • May be remarkable for hemolysis, hemoglobinuria, and hematuria
    • Coagulopathy may be present (elevated fibrin split products, decreased fibrinogen concentrations, and a positive D-dimer)
    • Increased PT and PTT


  • Local wound care and tetanus prophylaxis
  • Antibiotics are indicated only if signs of infection exist; secondary infections are uncommon
  • Although some texts recommend dapsone, it has been shown to be of limited benefit and is associated with hemolysis (in G6PD patients) and methemoglobinemia


  • Typically discharge home

See Also


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