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Brown Recluse Bites (Loxoscelism)

Ashley Zeoli


  • Only a handful of spiders are truly harmful to humans
  • The brown recluse (a member of the Loxoceles genus) is widespread in the South, West, and Midwest US
  • They are often found in homes (attics, basements, cupboards) and outdoors (rock piles and under tree bark)
  • Their numbers increase in association with humans (i.e. synanthropic)
  • Appearance/identification:
    • Brown recluses have three pairs of eyes, a monochromatic abdomen and legs, and very fine hairs on its legs
    • Using the “violin” pattern on its body is a poor way to identify this spider, as other harmless spiders can have similar markings.
  • Loxocelism is the medical manifestation of the brown recluse spider bite
  • Venom contains insecticidal toxins, metalloproteases, and phospholipases


  • Bites are most common on the upper arm, thorax, or inner thigh
  • Local signs:
    • Sometimes painless, but can cause burning sensation with two small cutaneous puncture marks with surrounding erythema. Pain can increase over the first 8 hours
    • Usually appears as a red plaque or papule with central pallor and can sometimes present with vesiculation
    • Usually self-resolves in 1 week
  • Skin necrosis:
    • In some, skin lesion can progress to necrosis overall several days
    • An eschar will form that eventually ulcerates
    • Usually will heal over several weeks to months
  • Systemic signs:
    • The degree of systemic effects does not correlate with the appearance of the bite
    • Symptoms may develop over several days, and include nausea, vomiting, fever, rhabdomyolysis, malaise, acute hemolytic anemia, significant swelling from head/neck bites that can compromise the airway, DIC and renal failure


  • Presumptive diagnosis is based clinical presentation of the bite/wound
  • DDx includes vasculitis, pyoderma gangrenosum, cellulitis, or other arthropod bites
  • Definitive diagnosis is based upon observing a spider bite in combination identification by an entomologist. There is an assay for Loxoceles venom, but it is not commercially available
  • Patients with local symptoms do not need any further workup
  • Patient with any systemic symptoms require lab evaluation for more serious disease:
    • CBC, UA to eval for blood, CMP, CK
    • If anemia: Type and Screen, peripheral smear, reticulocyte count, LDH, haptoglobin, coags to evaluate for hemolysis or DIC

Loxocelism flowchart

Loxocelism flowchart


  • Local signs:
    • Wound care (soap/water, elevation)
    • Pain management
    • Tetanus vaccine/prophylaxis if indicated
    • Antibiotics only if signs of concurrent cellulitis
  • Skin necrosis:
    • Symptomatic and supportive care
    • Surgical intervention can worsen cosmetic outcomes and is rarely indicated in the acute care setting. Skin grafting is occasionally needed for a very large ulcerative wound that is not healing. Infection is rare, Furthermore, the ulcerative base of the wounds often have a yellow stringy material that is not pus or infection. Please call Toxicology with any questions regarding brown recluse bites
  • Systemic signs: Targeted at treatment of symptoms that develop (Consult toxicology)
    • Hemolytic anemia: transfuse for Hgb <10 + consult heme
    • Rhabdomyolysis: LR for UOP >200-300cc/hr
    • If patient develops chest pain, obtain EKG and check a troponin; if either is abnormal please obtain echo and call Toxicology as heart effects (i.e. myocarditis) is something we have been seeing at VUMC
    • DIC: supportive care