Brown Recluse Bites (Loxoscelism)

Ashley Zeoli and Matthew Kern

Background

  • Only a handful of spiders are truly harmful to humans
  • The brown recluse (a member of the Loxosceles 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:
    • Three pairs of eyes, a monochromatic abdomen and legs, very fine hairs on legs
    • Using the “violin” pattern on its body is a poor way to identify this spider, as other harmless spiders can have similar markings
  • Loxoscelism is the medical manifestation of the brown recluse spider bite
  • Venom contains insecticidal toxins, metalloproteases, and phospholipases

Presentation

  • Bites are most common on the upper arm, thorax, or inner thigh
  • Local signs:
    • Usually painless, but can cause burning sensation with two small cutaneous puncture marks with surrounding erythema o Usually appears as a red plaque or papule with central pallor, sometimes with vesiculation
    • Usually self-resolves in 1 week
    • Skin necrosis (10-20% of cases): o Lesion can progress to necrosis overall several days
    • An eschar will form that eventually ulcerates o Usually will heal over several weeks to months
  • Systemic signs (rare, but more common in children):
    • The degree of systemic effects does not correlate with the appearance of the bite
    • Symptoms 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. Myocarditis is a rare adverse effect that may occur.

Evaluation

  • 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
  • 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” without RBCs, CMP, CK
  • If anemia: Type and Screen, peripheral smear, reticulocyte count, LDH, haptoglobin, coags to evaluate for hemolysis or DIC

Flowchart of management protocol borrowed from VUMC Children’s Hospital.

Management

  • 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: generally, transfuse to keep hgb > 9-10. However, the rapidity of hemolysis is more important than the hgb for determining when to transfuse but almost always the threshold is higher than other forms of anemia.
    • 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
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