Loxosceles and Necrotic Arachnidism

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Loxosceles spiders have a worldwide distribution. There are 18 species in the genus Loxosceles in North America, with 13 of these found in the United States. Five of these, L. reclusa, L. laeta, L. refuscens, L. arizona, and L. unicolor, have been associated with ulcers and necrotic skin lesions. L. reclusa (the brown recluse spider) is one of the most common species found in the United States and has been reported in over 20 states, particularly those in the region of the Missouri, Ohio, and Mississippi river basins, but also in several southwestern, southern, and midwestern states. L. reclusa prefers warm dry areas such as abandoned buildings, wood piles, and cellars and is generally nocturnal in activity. It is difficult to find the exact incidence of severe bites from these spiders, although one U.S. study of 460

deaths from venomous bites attributed 63 (14 percent) to L. reclusa. Loxoscelism is the reaction to the envenomation by species of the brown spider.

CLINICAL FEATURES Bites by Loxosceles spiders are initially painless, prohibiting definitive identification of the spider. The most common manifestation of a Loxosceles bite consists of a mild erythematous lesion that may become firm and heal with little or no scar over several days to weeks. 9 Occasionally, a more severe reaction occurs, with mild to severe pain several hours after the bite. There may be erythema and blister formation and bluish discoloration within the first 24 h ( Fig

188-4). This lesion may become necrotic over the next 3 to 4 days (Fig 188-5), with eschar formation by the end of the first week. These lesions may vary in size from

FIG. 188-4. Brown recluse spider bite approximately 12 h old. Note central hemorrhagic vesicle with surrounding spread of toxin. (Reproduced by permission from Management of Wilderness and Environmental Emergencies. St. Louis: Mosby, 19B9.)
What Considered Urin Discoloration

The necrosis is caused by aggregation of leukocytes and platelets forming a hemostatic plug in venules and arterioles. The bite of the brown recluse spider also may cause systemic involvement, which generally occurs within 48 h of the bite. The patient may experience fever, chills, nausea, vomiting, myalgias, arthralgias, petechiae, and hemolysis. Hemolysis is apparently mediated by direct effect of the spider venom on red blood cell membranes and may be severe, causing hemoglobinuria, renal failure, DIC, and rarely, death. Systemic reaction is more common in children and almost all deaths are reported in children under 7 years of age. There may be little correlation between systemic symptoms of Loxosceles envenomation and the severity of the skin lesions.

The venom of Loxosceles consists of multiple proteases, alkaline phosphatase, lipase, anaronidase, and other substances that involve the complement system. It is still unclear which of these substances is the major factor related to the necrosis-producing activity of the spider.

DIAGNOSIS In the United States, L. argiope, L. atrax, L. chiracanthium, L. lycosa, Tegenaria agrestis and numerous other varieties can all cause bites similar to that of L. reclusa.10 Although the brown recluse spider is the most renowned biting spider to produce necrotic lesions in humans, the most common biting spider in the United States is the so-called jumping spider, one of the Phidippus species. These small, furry, and relatively aggressive spiders are sometimes confused with the black widow spider because of their black and red markings. Although jumping spiders bite and tend to hang onto the victim and can lead to a necrotic lesion, they generally only produce a local reaction, which may take hours to days to subside.

In patients suspected of having a bite from L. reclusa and exhibiting signs and symptoms of envenomation, a complete blood count (CBC), creatinine, blood urea nitrogen (BUN), and coagulation profile should be ordered, as well as an urinalysis for hemoglobinuria. No laboratory tests yet exist to confirm bites of Loxosceles.

TREATMENT Treatment of a brown recluse or any necrotic spider bite should include the usual supportive measures. No antivenom is available commercially. For those bites with cytotoxic reactions and necrosis, tetanus prophylaxis and daily wound care should be given. Antibiotics should be used if evidence of infection exists. In some cases, analgesic therapy will be required. In general, surgery should not be done until the necrotic ulcers are greater than 2 cm in diameter and the borders of the ulcers are well established, usually 2 to 3 weeks after the bite.

Dapsone has been suggested by some clinicians to prevent ongoing necrosis from L. reclusa bites by inhibiting local infiltration by polymorphonuclear leukocytes, although there are no controlled data to substantiate this claim. More recently, hyperbaric oxygen has been proposed as treatment for severely necrotic Loxosceles bites based on case reports. However, controlled trials in animals failed to demonstrate superiority of this treatment over simple supportive wound management. 11

Adults and children with evidence of a significant systemic reaction to a brown recluse spider bite warrant hospitalization and close observation. If hemolysis occurs, appropriate hydration, red blood cell transfusion, and monitoring of renal function are important to avoid complications such as acute renal failure.

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