CASE #2: Brown recluse spider bite
Although most spider bites are not substantially venomous to humans, the brown recluse spider, Loxosceles reclusa, can cause significant cutaneous injury. These spiders are common inhabitants of homes and yards in the southeastern United States. Envenomation typically occurs when the victim comes in contact with spiders hidden in clothing, bedsheets, blankets, and storage items. Loxoscelism describes the systemic effects caused by envenomation from these spiders.
The physical reaction to a brown recluse spider bite depends on the quantity of venom injected and an individual’s sensitivity to toxins produced by the spider, particularly sphingomyelinase D, which triggers inflammation and is the primary venom dermonecrotic factor. The toxin depletes serum hemolytic complement, prolongs the activated partial thromboplastin time, and depletes clotting factors VIII, IX, XI, and XII. Following envenomation, the initial injury is endothelial damage of the arterioles and venules as these vessels become occluded with thrombi made up of neutrophils and platelets. Although most bites usually heal within three weeks, approximately 20% develop necrotic ulcers that may require months to heal and often result in permanent scarring.4
Spider bites can be difficult to diagnose clinically because the specific arachnid is unavailable for identification in the majority of cases. The initial bite rarely results in any immediate pain, making it difficult for the patient to collect the suspected brown recluse spider for identification. If the patient does recognize the spider, proper identification can help eliminate the confusion surrounding diagnosis. Recluse spiders are generally distinguished by their fiddle- or violin-shaped brown markings on the dorsal surfaces, but various species of gray, tan, or brown spiders have similar markings that can confuse identification. Other characteristic features of recluse spiders include six eyes arranged in three pairs and an abdomen covered with fine hairs and lacking coloration patterns.
Within 24 hours after the bite, the affected local area surrounding the site may exhibit the “red, white, and blue sign” due to erythema, vasoconstriction, and thrombosis. The necrotic lesion that develops is usually one to three inches and appears as a dry, sinking, bluish patch with irregular edges, a pale center, peripheral redness, and central blistering. The necrotic ulcer can persist for several months, leaving a deep scar. Systemic symptoms include chills, nausea, vomiting, myalgias, joint pain, and seizures. More serious systemic side effects, which are common in children and within the first 72 hours of the bite, include such hematologic conditions as thrombocytopenia, hemolysis, and renal-failure convulsions. Major complications occur in only a small minority of cases, and the need for surgery or complicated treatment is minimal.
It is difficult to diagnose a brown recluse spider bite solely on the basis of wound characteristics. Pain is the most common symptom and arises from either ischemia secondary to vasospasm or to disruption of myelin sheath on nerve fibers. In terms of differential diagnosis, the necrotic lesion from the spider bite can result from such other sources as staphylococcal or streptococcal infections, viruses, fungi, arthropods (non-recluse spiders, centipedes, ticks, mites, and so forth), neoplasia, and burns. Because numerous diseases mimic loxoscelism and there are no commercially available venom assays for humans, diagnosis of loxoscelism is questionable unless the origin of a Loxosceles spider bite is certain.
Several treatment approaches have been suggested. Initially, first-aid care should include application of aloe vera and ice, local wound care, and tetanus prophylaxis. The basic principle for conservative management involves rest, ice, compression, and elevation. Heat should be avoided, as it is believed to accelerate necrosis by enhancing the effects of sphingomyelinase D. As the wound spreads, specific therapies that can be administered include hyperbaric oxygen, dapsone, antihistamines, prophylactic antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage, and surgical excision.5
Patients with wounds that show signs of tissue breakdown should be administered prophylactic erythromycin or cephalosporin to prevent secondary infection (e.g., cellulitis). Antihistamines can also help relieve pruritus and swelling.
For individuals with moderate-to-severe bites, dapsone should be prescribed orally for 50 mg/day with an increase to 100 mg/day if necessary. Dapsone limits the severity of the spider bite by inhibiting neutrophil migration and endothelial attachment. Side effects may include sore throat, pallor, agranulocytosis, aplastic anemia, and cholestatic jaundice. One major concern with using dapsone is that it causes some degree of hemolysis in all patients, particularly those who are deficient in glucose-6-phosphate dehydrogenase.
Surgical excision is another proposed treatment for bites from the brown recluse spider. Excision is particularly useful in cases featuring large, stabilized lesions. In one clinical study, pretreatment with dapsone reduced excision complications and improved the symptomatic and cosmetic outcomes of patients bitten by L. reclusa.6 However, excision has been shown to delay wound healing if the lesion is excised early, as this may potentiate inflammation and venom effects.
Hyperbaric oxygen and nitroglycerin are other specific solutions that have been postulated to treat necrotic lesions. Hyperbaric oxygen may promote angiogenesis and formation of granulation tissue at the lesion site, thereby increasing the rate of healing. Nitroglycerin is used as a treatment modality because its local vasodilatory effects may lessen the effects of envenomation-induced vasoconstriction.
Overall, clinicians should only diagnose brown recluse spider bites if recluse spider involvement can be definitively proven. If diagnosed, management of systemic reactions of loxoscelism should require patients to be monitored for serial blood counts for such conditions as hemolysis, thrombocytopenia, and leukocytosis. In general, most brown recluse spider bites will heal without treatment. Approximately 10% to 15% of bite cases lead to such major complications as unacceptable scarring, chronic lesions, and hospitalization.7 Nevertheless, clinicians ought to acquire the comprehensive background of knowledge including the bite history, physical manifestations, and patient profile to handle the minority of cases that lead to dire outcomes.
At the patient’s two-week follow-up examination, the bite area showed only dried necrotic tissue.
Mr. Mudigonda is a graduate of the University of Notre Dame, South Bend, Ind., and a research fellow in the surgery branch at the National Cancer Institute, Bethesda, Md. Dr. Scheinfeld is assistant clinical professor of dermatology at Columbia University in New York City, where he has a private practice. Neither author has any relationship to disclose relating to the content of this article.
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All electronic documents accessed October 15, 2010.