Pediatric emergency medicine trisk 2001 2001
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FIGURE 90.16 The potentially lethal scorpion Centruroides exilicauda (sculpturatus).
(Courtesy of F. E. Russell.)
Spiders
Current evidence. There are more than 100,000 species of spiders (class
Arachnida). Most spiders are shy creatures, will not bite unless provoked, and
have mild venom and fangs that are too short and fragile to penetrate human skin.
Some of the most dangerous species in the United States are the brown recluse
and the black widow.
Loxoscelism (Bite of the Brown Recluse Spider). Current evidence. Three
species of Loxosceles have caused envenomation, primarily in the southern and
midwestern states, but can be found throughout the continental United States.
They are small (1 to 1.5 cm in length) with a brown violin-shaped mark on the
dorsum of the cephalothorax. They are found outdoors but will establish nests
indoors, especially in closets. As its name implies, the most common species,
Loxosceles reclusa, is shy and will only attack when provoked. Most bites occur
in bedrooms or while dressing. The venom is cytotoxic and also contains a factor
similar to hyaluronidase.
Clinical recognition. The bite is usually innocuous and may initially go
unnoticed. The spectrum of reaction ranges from minor local reaction to severe
necrotic arachnidism ( Fig. 90.17 ). The local reaction consists of mild to
moderate pain 2 to 8 hours after the bite, with erythema and a central blister or
pustule. Within 24 hours, there is subcutaneous discoloration that spreads over 3
to 4 days, reaching a size of 10 to 15 cm. At this time, the pustule drains,
producing an ulcerated “crater.” Scar formation is rare if there is no evidence of
necrosis within 72 hours of the bite. Alternative diagnoses should be considered if
