Consultant.
No. 12
Necrotic Skin Lesions:
Spider Bite—or Something Else?
By ROCKY BENOIT, MD and JEFFREY R. SUCHARD, MD |
October 1, 2006
University of California, Irvine
Dr Benoit is a resident physician in the department of emergency medicine and Dr Suchard is associate professor of clinical emergency medicine and director of medical toxicology in the department of emergency medicine at University of California, Irvine Medical Center in Orange.
WHY MISDIAGNOSIS PERSISTS
At least 3 reasons account for the persistent misdiagnosis of unexplained lesions as spider bites by many patients and some health care professionals:
- Arachnophobia is a common fear. It is easy, and perhaps oddly comforting, to ascribe unexplained and potentially frightening symptoms to spider bites. In the United States, the spider most commonly implicated as the cause of dermonecrotic lesions is the brown recluse (Box).10-13
- Patients often have difficulty in accepting that a medical problem has an endogenous origin. They prefer to blame an external agent, such as a poison or envenomation.
- Some health care professionals may find it easier to rely on the diagnosis of "spider bite" than to generate an adequate differential diagnosis for a skin lesion of unknown origin.
DIFFERENTIAL DIAGNOSIS
Although spider bites can produce dermonecrotic wounds, the differential diagnosis of such lesions is extensive; it includes microbial infections, dermatologic disorders, vasculitides, and environmental exposures (Table).14-16
| | | | | | Table —Medical conditions that have been misdiagnosed as spider bites | | | |
| | | Bacterial infection
Staphylococcus/Streptococcus infection (most common)
Lyme disease (erythema chronicum migrans)
Disseminated gonococcemia
Rocky Mountain spotted fever
Purpura fulminans
Syphilitic chancre
Cutaneous anthrax | | |
| | | Viral infection | | | Herpes simplex | | | Herpes zoster | | |
| | | Fungal infection | | | Sporotrichosis | | |
| | | Vasculitis | | | Thromboembolic skin necrosis (warfarin skin necrosis) | | | Focal vasculitis | | | Polyarteritis nodosa | | |
| | | Dermatologic conditions | | | Toxic epidermal necrolysis
Stevens-Johnson syndrome
Pyoderma gangrenosum
Erythema multiforme/nodosum
Lymphomatoid papulosis
Squamous cell carcinoma | | |
| | | Bites and stings from other insects or animals | | | | Especially from blood- serum-sucking bugs | | | | |
| | | Miscellaneous
Poison ivy/oak dermatitis
Chemical burn
Bed sore
Localized drug reaction
Diabetic ulcer
Factitious/psychogenic dermatitis
Pilonidal sinus | | |
| | | |
Exonerating the Oft-Accused Brown Recluse
The brown recluse--the spider most commonly implicated in alleged bites--lives and breeds predominantly in the south central United States. Yet complaints of brown recluse spider bites are ubiquitous.10-12 In one study, a total of 216 cases of brown recluse spider bites were diagnosed in California, Oregon, Washington, and Colorado during a 41-month period, yet only 17 Loxosceles reclusa specimens have ever been verified in these states.10 Because public reporting of spider bite diagnoses is not required, the number of misdiagnoses noted in this study is likely a gross underestimate of the actual total.
When confronted with evidence of geographic improbability, patients with an alleged brown recluse spider bite commonly respond that the spider was recently imported from an area where it is endemic.13 In California, a common assumption is that the bite was caused by a cousin of the brown recluse spider (Loxosceles deserta). Maps of the number of reported spider bite cases in the United States indicate that the highest number of cases are in the most densely populated areas, irrespective of the spider's confirmed habitat.10 These data suggest that the larger the population of a given area, the higher the incidence of dermo-necrotic lesions of unknown origin, which may be attributed to spider bites.
