Arachnid Bite Reactions

Brown Recluse Spider Bites

Basics

Most spiders are harmless to humans. Only the six-eyed brown recluse Loxosceles (discussed in this chapter) and the black widow spider have ever been associated with significant disease and very rare reports of death.
Deaths from brown recluse spiders have been reported only in children younger than 7 years.
Brown recluse spiders are native to the midwestern and southeastern United States. With increasing travel, individual spiders and spider bites can be found in areas where the spider is not endemic, and health care practitioners should consider this when diagnosing and treating suspected bites.
Brown recluse spiders are notable for their characteristic violin pattern on the back of the cephalothorax. The violin pattern is seen with the base of the violin at the head of the spider and the neck of the violin pointing to the rear (Fig. 29.5). These small spiders are yellowish tan to dark brown in color with darker legs.
They are not aggressive and bite only when threatened, usually when pressed up against the victim's skin. They seek out dark, warm, dry environments such as attics, closets, porches, barns, basements, woodpiles, and old tires.

Clinical Manifestations

The severity of symptoms can range from a minor reaction, a localized to slow-healing ulcerated lesion, to a systemic vascular reaction with renal damage that can be life-threatening with thrombocytopenia, disseminated intravascular coagulopathy, and renal failure.
The initial bite is typically painless, but symptoms develop about 2 to 8 hours later, area becomes painful and swollen.
A “bull's eye” lesion may form.
Over days the blister forms a crust, which hardens and falls off to leave behind an ulcerated depression.
The ulcer heals over months and leaves behind a scar.

Management

An attempt should be made to identify the offending spider to ensure proper management.
General measures that should occur after a spider bite include the following:
- The bitten area should be washed with soap and water.
- Application of an ice pack wrapped in cloth to the site.
- Analgesics.
- Seek immediate emergency care for further treatment.
Treatment involves supportive care including the use of systemic antibiotics to prevent infections and antihistamines to reduce swelling.
Antivenom for bites by Loxosceles genera is very effective if given soon after the bite.
Systemic steroids may be of benefit.

Helpful Hints

It is believed that the vast majority of reported brown recluse bites have been greatly overdiagnosed.
Conditions that are far more common and more likely to be the source of necrotic wounds that have been initially misdiagnosed as recluse spider bites by medical professionals include: infection by Staphylococcus, Streptococcus, herpes simplex, diabetic ulcers, and pyoderma gangrenosum (Fig. 29.6).