PROBLEM

A 22-year-old man from Virginia presents with a fever and dark rash on his left hand. Several days ago, he noticed a red spot on the back of his hand. He originally assumed it was an insect bite. When it turned dark, he decided to seek medical attention. On examination, the patient's temperature is 100 F (37.8C). On the dorsum of his left hand is a 2 2-cm ulcer with eschar around the edges. On further questioning, he tells you that he spent the previous week cleaning his basement.

APPROACH

Brown recluse spiders (Loxosceles species) are rare outside endemic areas. They are most commonly found in the south central United States, particularly Kentucky, Tennessee, Arkansas, Missouri, Oklahoma, and Kansas. In fact, bites and ulcers attributed to these spiders in areas outside endemic regions should be viewed with skepticism. These spiders are nocturnal and like to dwell in closets, clothing, or blankets. Identification ultimately depends on recognizing the spider's eye pattern (most spiders have 8 eyes, but recluse spiders have 6) and the well-known violin pattern on its thorax (commonly misidentified). Since victims rarely bring in the spider for identification, it is difficult to be certain about the diagnosis.

TABLE 1. Differential for necrotic cutaneous ulcers

A number of other diagnoses require consideration when a patient presents with a necrotic ulcer (see Table 1). Unless the patient is from an endemic area, the lesion is probably not the result of a brown recluse spider bite.

MANAGEMENT

Most brown recluse spider bites result in mild inflammation and have a self-limited course. Necrotic ulcers are less frequent. Elevation, ice, and local wound care suffice for most bites. The use of more aggressive therapy is controversial. Many have been advocated, including hyperbaric oxygen, dapsone, corticosteroids, excision and grafting, and antivenom (not available in the United States). None of these therapies has been confirmed to work in randomized controlled trials. More harm may be done by these treatments, especially since most cases of recluse bites are not verified by an arachnologist and, even if they are, tend to be self-limited.

This patient did not have a brown recluse spider bite. Virginia is not in an endemic area for this spider. Culture of the wound grew group A streptococcal bacteria. (Note that obtaining routine cultures of wounds or ulcers is becoming more important in light of the increased incidence of community-acquired methicillin-resistant Staphylococcus aureus). In addition to local wound care, the patient received penicillin V potassium, 500 mg po q6h for 10 days, and had an uneventful recovery.

CONTRIBUTOR

DEAN G. GIANAKOS, MD, Associate Professor of Clinical Family Medicine, University of Virginia; Associate Director, Lynchburg Family Medicine Residency, Lynchburg, Va; and a member of the Patient Care Board of Editors.

REVIEWER

KARL SINGER, MD, Medical Director of Patient Care; and family physician and general internist, Exeter Family Medicine Associates, Exeter, NH.

What would you do if . . .

1. The patient told you he was a government employee and was concerned about a bioterrorist attack?
2. The patient received dapsone, and severe anemia subsequently developed?

Answers

1. Consider cutaneous anthrax, which can present as a necrotic ulcer.
2. Dapsone can cause hemolytic anemia, especially in patients with glucose-6-phosphate dehydrogenase deficiency.

For more on this topic . . .

Hogan CJ, Barbaro KC, Winkel K. Loxoscelism: old obstacles, new directions. Ann Emerg Med. 2004;44:608-624.

Swanson DL, Vetter RS. Bites of brown recluse spiders and suspected necrotic arachnidism. N Engl J Med. 2005;352:700-707.