Necrotic Arachnidism – 5 Interesting Facts
- History of a spider bite and identification of the offending spider is the only definitive test.
- Within 6 to 12 hours, a small papule develops at the bite site, surrounded by edema.
- In about 90% of cases, the response is limited to a local urticaria-like or cellulitis-like reaction.
- RICE therapy—rest, ice compresses for 15 min/hour, and elevation.
- Aspirin for pain relief and to reduce thrombosis and a tetanus booster shot (if not up to date).
Terminology
- Necrotic arachnidism is the term used for all necrotic spider bites. Loxoscelism is a term reserved for reactions to bites of the brown recluse spider and members of that same genus. Brown recluse spiders are normally found outdoors—under rocks, cliffs, and areas that afford protection—but this spider readily adapts to indoor habitats as well.
- There are 13 species of Loxosceles, with 5 causing cutaneous loxoscelism (Loxosceles reclusa, Loxosceles deserta, Loxosceles arizonica, Loxosceles laeta, and Loxosceles rufescens).
- The brown recluse is sometimes called the violin spider because of a violin-shaped marking on the dorsum. Brown recluse venom contains at least nine identified protein fractions; the most important to cutaneous reactions is a substance called sphingomyelinase D2.
Etiology and Risk Factors
- The true prevalence of spider bites is unknown, but about 10,000 spider bites are reported to poison control centers in the United States each year.
Diagnosis
Approach to Diagnosis
- History of a spider bite and identification of the offending spider is the only definitive test.
- In the absence of a captured spider, the clinical presentation remains the principal means of diagnosis.
Workup
Physical Examination
- A brown recluse spider bite is usually painless.
- Within 6 to 12 hours, a small papule develops at the bite site, surrounded by edema.
- Constitutional symptoms are variable and include malaise, headache, arthralgias, fever, nausea, vomiting, and, occasionally, a nonspecific maculopapular eruption.
- In about 90% of cases, the response is limited to a local urticaria-like or cellulitis-like reaction.
- In less than 10% of cases, and within 2 to 3 days, the site begins to demonstrate early signs of hemorrhage and necrosis, with a central gray to violaceous center, surrounded by a white ring, and then by erythema, the so-called red, white, and blue sign.
- Ulcers caused by the brown recluse spider characteristically heal very slowly.
- Rarely reported complications may include a Coombs-positive hemolytic anemia, disseminated intravascular necrosis, seizures, renal failure, and even death.
Laboratory Tests
- In severe cases, serial CBC testing because of possible hemolysis and thrombocytopenia and serial urinalysis to rule out hemoglobinuria may be performed.
Diagnostic Procedures
- Biopsies are not diagnostic but may reveal findings consistent with a spider bite. A biopsy is not typically performed unless there is desire to exclude other ulcerative conditions.
Treatment
Nondrug and Supportive Care
- Mild Cases
- RICE therapy—rest, ice compresses for 15 min/hour, and elevation.
- Aspirin for pain relief and to reduce thrombosis and a tetanus booster shot (if not up to date).
Drug Therapy
- Severe Cases
- Dapsone use is controversial. Animal studies have produced mixed results. In one uncontrolled human study, patients treated with dapsone required less surgery and had better clinical outcomes. Some studies have indicated that to have any efficacy, dapsone must be initiated in the first 36 hours after the bite.
- The use of systemic corticosteroids is advocated by some authorities, but six animal studies and human studies have failed to demonstrate any definitive benefit on lesion size or progression with corticosteroids.
- Brown recluse specific antivenin exists but must be administered within the first 24 hours.
Treatment Procedures
- Surgical excision has been advocated by some, but others think that it is contraindicated and can actually be detrimental. Most authorities advocate surgery only for late-stage, stabilized lesions.
References
1.Elston DM, Miller SD, Young RJ III, et al. Comparison of colchicine, dapsone, triamcinolone, and diphenhydramine therapy for the treatment of brown recluse spider envenomation: a double-blind, controlled study in a rabbit model. Archives of dermatology. 2005;141(5):595-597. Reference
