Podcast #106 – Brown Recluses: This IS the Spider You Were Looking For


Patients often come in complaining of a possible spider bite, but is this actually the cause of their symptoms?  In this blog and podcast, we talk specifically about brown recluse bites, differentiating them from other causes, treatment, and other pearls.
​Staph infections, especially MRSA, are often thought by patients to be brown recluse bites when in fact these bites are very uncommon.  Indeed, prior evidence has demonstrated that the likelihood of MRSA is significantly increased if a patient says they have a spider bite but did not see a spider or feel its bite.  This time we discuss how to recognize and manage brown recluse bites.

Brown recluse spiders are most abundant and active at night during the warm months, are non-aggressive, reclusive, and prefer to retreat when threatened.  Brown recluse spiders measure 2-3 cm from leg to leg, have 6 eyes arranged in 3 pairs (most spiders have 4 pairs), and has a characteristic dark, violin-shaped spot on the dorsal aspect of the cephalothorax.

Envenomation can result in dermonecrosis and, less commonly, a potentially fatal systemic illness that includes hemolysis with DIC, thrombocytopenia, proteinuria, and rhabdomyolysis, with subsequent renal failure.  Death in the United States is extremely rare.  The venom contains cytotoxic, proteolytic, coagulopathic, and hemolytic components. The primary toxic component is sphingomyelinase D, which is largely responsible for necrosis and hemolysis. Hyaluronidase causes the characteristic gravitational spread of the lesion.

Brown spider bites typically occur during dressing or sleeping when spiders become trapped in clothing or bed linens. The bite can produce a sharp, stinging sensation, although frequently the victim is unaware of having been bitten.  Over time, the wound typically develops an erythematous halo surrounding a central hemorrhagic vesicle.  Occasionally, the central vesicle will be surrounded by an area of ecchymosis, surrounded by a ring of pallor and an outer ring of redness.  As early as 24 hours after envenomation, fever, arthralgias, nausea, vomiting, diarrhea, rash, myalgias, and headache can develop.  By day 3 or 4, the hemorrhagic vesicle becomes necrotic, and an eschar forms.  After 2-5 weeks, the eschar sloughs, leaving an ulcer that often heals by secondary intention, though some may require skin grafting.  In severe cases, there can be progressive tissue necrosis that is particularly severe in fatty regions such as the buttocks or thighs.  Below is an example of wound progression in a 10 year old girl in New Mexico.


Diagnostic Pearls
Severe burning, pain, and pruritus at the bite site within 2-6 hours is characteristic of a brown recluse envenomation.

The mnemonic “NOT RECLUSE” lists the features of look-alike conditions. The presence of each makes the diagnosis of brown recluse spider bite unlikely:

  • Numerous: for brown recluse spider, there is typically one bite.
  • Occurrence: lack of history of the spider being disturbed, such as cleaning out boxes in an attic, makes diagnosis unlikely.
  • Timing: bites outside the April to October time frame (in the United States) are usually not brown recluse.
  • Red center: usually the center of brown recluse bite is white, purple, or black.
  • Elevated: brown recluse spider bites are usually flat, or even depressed.
  • Chronic: most bites are healed by 3 months.
  • Large: largest bites are 10 cm. Any larger ulcerated lesion suggests the diagnosis of pyoderma gangrenosum.
  • Ulcerates too early: usually, ulceration occurs after 7-14 days.
  • Swollen: usually, bites do not lead to edema, except above the neck and on the feet.
  • Exudative: bites are not purulent. A small vesicle at site of bite may be seen.

First aid treatment includes:

  • Wound irrigation (may affect size and degree of envenomation)
  • Cold compresses intermittently over 72 hours (inhibits sphingomyelinase D activity)
  • Elevation / immobilization of the bitten extremity
  • Analgesics
  • Antihistamines

Hospital treatment includes:

  • Wound irrigation
  • Cold compresses
  • Elevation / immobilization of the bitten extremity
  • Tetanus prophylaxis as indicated
  • Conservative, local debridement of clearly necrotic tissue

Other treatments:

  • Early excision of bite lesions – contraindicated
  • Topical nitroglycerin – anecdotal reports; animal study showed no benefit
  • Intralesional injection of steroids – no benefit
  • Systemic steroids – possibly effective for severe systemic involvement (hemolysis), but no benefit for local lesions
  • Antibiotics – no proven efficacy, but have a low threshold for beginning if there is any suspicion of incipient cellulitis
  • Dapsone – not FDA approved for this indication; data inconclusive; if used, check glucose-6-phosphate dehydrogenase level
  • Hyperbaric oxygen – data inconclusive; may use if convenient access is available
  • Antivenom – only available in South America; data limited

This was a great review and several sources were used.  However one of the best sites that did a very good job with summarizing the information (as well as having additional details) is VisualDx which is a paid service but well worth it if you need to learn more about dermatology.

Let us know what you think by giving us feedback here in the comments section or contacting us on Twitter or Facebook.  Remember to look us up on Libsyn and on iTunes.  If you have any questions you can also comment below, email at thetotalem@gmail.com, or send a message from the page.  We hope to talk to everyone again soon.  Until then, continue to provide total care everywhere.

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