Brown recluse spider bite


Brown recluse range (yellow area)
Brown recluse
  • 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

Brown recluse spider bite, day 3.
Brown recluse spider bite, day 4.
Brown recluse spider bite, day 5.
Brown recluse spider bite, day 6.
Brown recluse spider bite, day 9.
Brown recluse spider bite, day 10.
  • 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)

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

External Links