Morning Report: 5/30/2013

Brown Recluse Spiders

Species Facts:

“violin spider”
Loxosceles reclusa (genus name)
Sicariidae (family name)
- family of 6 eyed spiders known for their necrotic bites
- most spiders have 8 eyes
- Two genus in this family (Loxosceles and Sicarius)
- Genus Sicarius is known as the assassin spider
Lots of Loxosceles… (11 species)
- Apachea, arizonica, destera, laeta (cali, south america), rufescenes(Africa)

Identifying Markers:

Famous for…

Being shy – enjoying closed dark spaces, hates feeling intimidated
Local wound necrosis (dermonecrotic arachnidism)
Rarely – systemic illness and collapse
Being confused for MRSA, anthrax, herpes, diabetic ulcer, squamous cell CA
Being blamed for a lot of attacks (pts are unreliable for description of spiders)
Documented bites are rare

Number Facts:

2003: 2,843 brown recluse spider exposures reported to US poison centers; 40% of those were treated in a medical center
23.3% of all exposures were considered moderate to major with 1 death

Pathophysiology:

Venom includes:
- Sphingomyelinase D
  - primary dermonecrotic factors
  - disrupts cellular membranes
  - causes serotonin release
  - platelet aggregation and thrombosis of small capillaries
- Ribonuclease
- Hyaluronidase
  - facilitates the spread of the venom locally
  - enhances tissue destruction
- Deoxyribonuclease
- Lipase
- Phosphohydrolase
Cytotoxic elements of venom leads to endothelial cell damage
- This attracts neutrophils, which leads to more destruction
- PMLs also contribute to dermonecrosis
Venom causes erythrocyte hemolysis
Leukocytes release cytokines which activates the complement system

Clinical Presentation:

Initially mild bite and not noticed
Within 24 hours patients will present for treatment of a painful purple papule
Central purple lesion is surrounded by a blanched ischemic zone and rim of indurate erythema
Central papule can coagulate and become thrombosed
Results in necrotic, ulcerating wound
Eschar may slough off and extend into subcut fat; this may require surgical grafting
Systemic Loxoscelism – fevers, chills, nausea, arthralgias, morbiliform rash, hemolysis
- Can occur 24-72 hrs after bite and is not correlated with size or severity of skin reaction
Rarely – can present in DIC, renal failure, seizures

Diagnosis:

Treatment:

Generally all that is need is routine wound care, including tetanus
Routine antibiotics are not indicated
Only use surgical intervention for scar debridement (not to cut out necrotic tissue)
Supportive care for DIC, renal failure, ect.

Experimental Treatment:

Dapsone: theoretically inhibits PMLs from aggregating at the wound site and causing tissue necrosis, can reduce disfiguring ugly scars; data is limited
- But dapsone isn’t all that either – can cause hemolysis, methemoglobinemia (G6PD def)
Hyperbarics: Maynor et al showed that 48 hrs of HBO caused a 50% reduction in lesion size after experimental envenomation; possibly may cause reoxygenation of the wound and sequestration of PMLs away wound.; not approved by the US Undersea and Hyperbaric Medical Society as of yet.

Other Spiders Causing Necrosis:

References:

Brown recluse spider From: Habif: Clinical Dermatology, 5th ed.; Chapter 15 – Infestations and Bites >> SPIDERS BROWN RECLUSE SPIDER (GENUS LOXOSCELES)
Shannon: Haddad and Winchester’s Clinical Management of Poisoning and Drug Overdose, 4th ed.; Chapter 22 – Venomous Arthropods >> Spiders
Bites of Brown Recluse Spiders and Suspected Necrotic Arachnidism, N Engl J Med 2005;352:700-7.