Venomous Creatures: Brown Recluse Envenomation (Loxoscelism)

Spider bites are a common occurrence in the United States. While most bites are benign, there are two types of spiders with clinical importance to emergency physicians because their venom can cause significant systemic manifestations. These are widow spiders and recluse spiders. Missed diagnosis is common for both bite types, and delayed treatment can lead to significant morbidity. This article reviews the distinguishing characteristics of recluse spider bites, the clinical syndrome caused by recluse spider venom, ED management, indications for and dosing of antivenom, and disposition.

BACKGROUND

Recluse spiders, sometimes also called brown spiders, are difficult to identify from their non-venomous brown cousins. While a violin pattern is commonly cited as its most distinguishing feature, it is not present on all recluse spiders. The most accurate method of identification is counting 3 pairs of eyes, one in front and one on each side with a gap between each. However, these spiders are so small that identification is near impossible.

From: Vetter RS, Swanson DL. Bites of recluse spiders. UpToDate.

From: https://spiders.ucr.edu/brs.html

CLINICAL MANIFESTATIONS AND TREATMENT

The bite of a recluse spider is typically painless, and only when local and systemic manifestations occur is it suspected, frequently leading to delayed or missed diagnosis. Thus, a thorough history and physical exam is important for determining whether a bite was by a brown recluse.

The mnemonic NOT RECLUSE is helpful with the diagnosis:

• Numerous bites
• Occurrence in non-secluded location
• Timing from November to March
• Red center of the bite (instead of pale)
• Elevated bite area (instead of flat/sunken)
• Chronic symptoms
• Large (>10 cm)
• Ulceration in less than 1 week
• Swelling
• Exudative

The venom of the recluse spider contains many proteins and enzymes, the key of which is sphingomyelinase. Sphingomyelinase activates complement, induces neutrophil chemotaxis and keratinocyte apoptosis, and generates metalloproteinases. The resulting clinical syndrome is known as loxoscelism.

Within 2 – 8 hours, recluse spider bite victims might experience pain and note the development of a red papule at the bite site. This papule may be self-limited or develop into a dry eschar that ulcerates over the next few days. These lesions frequently heal by secondary intent and rarely require surgical intervention.  

Systemic manifestations, though rare, include angioedema, acute hemolytic anemia, disseminated intravascular coagulopathy, rhabdomyolysis, renal failure, coma, and death. Children are more likely to develop systemic loxoscelism.

All bites either confirmed or suspicious for a brown recluse bite should be reported to the Poison Control Center.

Labs:

• CBC w/peripheral smear
• Reticulocyte Count
• Type and Screen
• CMP
• Urinalysis
• LDH
• Haptoglobin
• CMP
• Calcium
• Phosphate
• Uric acid
• CK
• Coags
• Fibrinogen
• D-dimer
• Direct antibody testing (Coombs)

Antivenom is not commercially available in the United States

DISPOSITION

• Discharge: only local cutaneous effects
• Admit: systemic effects or abnormal lab values requiring monitoring and/or parenteral treatment

Resources:

• Chaves-Moreira et al. Journal of Venomous Animals and Toxins including Tropical Diseases. 2017;23:6.
• Gremski LH, Trevisan-Silva D, Ferrer VP, Matsubara FH, Meissner GO, Wille AC, et al. Recent advances in the understanding of brown spider venoms: From the biology of spiders to the molecular mechanisms of toxins. Toxicon. 2014;83:91-120.
• Hogan CJ, Barbaro KC, Winkel K.  Loxoscelism: Old Obstacles, New Directions.  Annals of Emergency Medicine.  2004;44(6):608-624.
• Nguyen N, Pandey M.  Loxoscelism: Cutaneous and Hematologic Manifestations. Advances in Hematology.  2019;Article ID 4091278, 6 pages.
• Pauli I, Puka J, Gubert IC, Minozzo JC. The efficacy of antivenom in loxoscelism treatment. Toxicon. 2006; 48(2):123–37.
• Robinson JR, et al.  Defining the complex phenotype of severe systemic loxoscelism using a large electronic health record cohort.  PLoS ONE.  2017;12(4):e0174941.
• Saucier JR. Arachnid Envenomation. Emerg Med Clin N Am.  2004;22:405-422.
• Stoecker WV, Vetter RS, Dyer JA.  NOT RECLUSE – A Mnemonic Device to Avoid False Diagnosis of Brown Recluse Spider Bites.  JAMA Dermatology.  2017;153(5):377-378.
• Tambourgi DV, Goncalves-de-Andrade RM, van den Berg CW. Loxoscelism: From basic research to the proposal of new therapies. Toxicon. 2010;56(7):1113–1119.
• Vetter RS, Swanson DL.  Bites of recluse spiders.  UpToDate.

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