Brown Recluse Spider Envenomation Clinical Presentation

Updated: May 16, 2017
  • Author: Thomas C Arnold, MD, FAAEM, FACMT; Chief Editor: Joe Alcock, MD, MS  more...
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Presentation

History

The brown recluse spider, living up to its name, is naturally nonaggressive toward humans and prefers to live in undisturbed attics, woodpiles, and storage sheds.

Brown recluse spiders vary in size and can be up to 2-3 cm in total length. They are most active at night from spring to fall.

Characteristic violin-shaped markings on their backs have led brown recluse spiders to also be known as fiddleback spiders.

Envenomation from the brown recluse spider elicits minimal initial sensation and frequently goes unnoticed until several hours later when the pain intensifies.

An initial stinging sensation is replaced over 6-8 hours by severe pain and pruritus as local vasospasm causes the tissue to become ischemic.

Symptoms of systemic loxoscelism are not related to the extent of local tissue reaction and include the following:

  • Morbilliform rash
  • Fever
  • Chills
  • Nausea
  • Vomiting
  • Joint pain
  • Hemolysis
  • Disseminated intravascular coagulation (DIC)
  • Renal failure
  • Seizures
  • Coma
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Physical Examination

Edema around the ischemic bite site produces the appearance of an erythematous halo around the lesion.

The erythematous margin around the site continues to enlarge peripherally, secondary to gravitational spread of the venom into the tissues.

Typically, at 24-72 hours, a single clear or hemorrhagic vesicle develops at the site, which later forms a dark eschar (see the image below).

Classic finding of a vesicle with surrounding eryt Classic finding of a vesicle with surrounding erythema at 24 hours following brown recluse envenomation. Photo by Thomas Arnold, MD.

Necrosis is more significant in the fatty areas of the buttocks, thighs, and abdominal wall (shown in the image below).

Spider bite, brown recluse. Within an hour, the bi Spider bite, brown recluse. Within an hour, the bite area swelled to the size of a quarter. The area turned blue and dark red by the evening of the first day, exceeding the boundaries of a circle drawn around the area of initial swelling by the patient's physician. Courtesy of Dale Losher.
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Causes

Dermonecrotic arachnidism has been described in association with several species of Loxosceles spiders, but, in the United States, L reclusa venom is the most potent and the most commonly involved.

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Complications

Delayed skin grafting may be necessary after 4-6 weeks of standard therapy.

Losses of digits and amputations have been reported.

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