Clinical Review

Bite of the Brown Recluse Spider

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The bite of the brown recluse spider (Loxosceles reclusa) has the potential for severe tissue necrosis. Unfortunately, such a wound can easily be misdiagnosed; the identity of the lesion must be confirmed so that appropriate treatment can be administered and complications avoided. Obtaining a detailed history, including where the bite was incurred, the body site, and patient symptoms and vital signs, are essential for optimal management.


 

References

The brown recluse spider (Loxosceles reclusa) is a small arachnid with great potential to inflict physical harm. More potent than a rattlesnake’s venom, the toxin emitted by the brown recluse has the ability to rupture cell membranes and destroy regional nerves, blood vessels, and fatty tissue. Envenomation by the brown recluse can lead to severe necrosis of the cutaneous tissues.1,2

In the United States, L reclusa is one of 13 species of Loxosceles—five of which have been associated with necrotic lesions resulting from bites and envenomation.3 Though rare, and virtually nonexistent across significant portions of North America,4 the brown recluse is often cited as the offending creature in reported bites involving envenomation5 (with reports sometimes outnumbering estimated numbers of specimens in a given area6). Considering the limited range within which the spider is considered endemic, any patient who presents reporting a possible brown recluse spider bite (or who presents with a wound suspected of being such a bite) must be questioned quickly and carefully. The first and foremost question: where, geographically, was the patient bitten?

Endemic Areas
Brown recluse spiders are known to be present in the subtropical areas of North America—but not in areas with high humidity. According to arachnologists in the southeastern United States, the closer one is to the Gulf of Mexico, the less likely one is to encounter a brown recluse.7 This spider is most commonly found in eastern Texas, Arkansas, areas west of the Appalachian Mountains, and northern areas of the Gulf Coast states (see Figure 18). They are virtually nonexistent along the Atlantic seaboard and the Gulf Coast,4 although lone specimens of Loxosceles species have been reported in numerous nonendemic areas, suggesting possible transport through commerce or family relocation.9 One suspected case of brown recluse envenomation was recently reported in New York State.10

If it is determined that the geographic area in question is indeed populated by brown recluse spiders, more detailed history must then be elicited from the patient regarding recent activities. The brown recluse may reside indoors and often hides in bed sheets, blankets, and stored clothing. This spider also may be found behind furniture, in basements and cupboards, or in other small, tight areas. It is commonly found in cardboard boxes stored in a closet or an attic,11 and boxes with folded flaps are a preferred dwelling place.7 (Thus, a remote chance that L reclusa can be inadvertently transported to a nonendemic area9 does exist.)

In the outdoors, the brown recluse may be found in woodpiles, piles of leaves or other natural debris, in outdoor sheds or garages, under rocks, and in other places that are relatively dark and seldom used.12

Patient Presentation/Patient History
Initially, patients with a brown recluse spider bite may present to a primary care provider with complaints of mild pain and itching, presumably around the bite site. Within eight hours, the pain becomes stabbing and penetrating and may give way to a burning sensation.7

Patients with a positive pertinent history who are at increased risk for a bite are those who live in areas where these spiders are endemic and who have been performing tasks in areas where these spiders might reside. Not wearing long pants and long-sleeved shirts contributes to the probability that a patient has sustained a bite.

Physical Examination
The site of the suspected bite and surrounding skin should be examined carefully. A pustule, generally small and white, may appear, surrounded by erythema. For as long as 24 hours following the time of the initial bite, a volcano-like lesion may be present, with a sunken central “crater” that has raised edges. While the center of the lesion is free of inflammation, the surrounding skin is typically red and inflamed.12

Pathologically, a specified sequence occurs following a bite with envenomation. Initially, platelets aggregate, followed by endothelial swelling and destruction (see Figure 2a). Gradually, this leads to the blocking of capillaries with white blood cells, which results in ischemia and ultimately necrosis.1

The clinical manifestations of the brown recluse spider bite may vary, based on the amount of venom injected and the age and overall health of the patient. One who has been bitten with minimal envenomation may experience little more than mild erythema, localized urticaria, and generalized discomfort that resolves spontaneously in three to five days.1

In patients who experience more significant envenomation, a “bull’s-eye” lesion may appear. The center of the wound may be bluish in hue, with concentric rings—an inner pale ring, and an outer reddened ring. The center of the wound subsequently forms a hemorrhagic bleb that will typically become necrotic. Eventually, as the eschar matures, the necrotic tissue will slough off, and an area of granulation will develop. Full healing of the wound may take from four weeks to as long as six months.1

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