Click to Enlarge Figure 4 | Click to Enlarge Figure 5 | Click to Enlarge Figure 6 |
| Photo Courtesy of Ted Rosen, MD | Photo Courtesy of Ted Rosen, MD | Photo Courtesy of Ted Rosen, MD |
The local inflammation and tissue necrosis associated with brown recluse spider bites results from the spider's venom, which contains enzymes and other products. Within 2 to 6 hours, the bite site becomes pruritic and burning pain, erythema, and swelling develop (Figure 4). Over the next several hours or days, a hemorrhagic vesicle appears and then ulcerates. Progression of the lesion results in a central bluish necrotic depression within surrounding erythema. A blanched ring may form around the necrotic area because of local vasoconstriction, giving the entire lesion a "red, white, and blue" appearance (Figure 5). The necrotic area then forms an eschar, which can take several weeks or months to heal (Figure 6).
Systemic signs and symptoms—such as arthralgia, rash, fever, vomiting, and hemolysis—are rare (between 0.7% and 1.8% of reported bites). The incidence of systemic loxoscelism is higher in children, perhaps because of the greater amount of venom injected per kilogram of body weight than in adults.
Management. Brown recluse spider bites have been treated with antibiotics, antihistamines, corticosteroids, dapsone(Drug information on dapsone), hyperbaric oxygen, nitroglycerine patches, surgical excision, and even direct high-voltage current from a stun gun. Few of these treatments have been tested, and none have proved beneficial.3,4 In most cases, the lesions heal with standard local wound care. Because the initial lesion results from envenomation rather than a bacterial infection, empiric antibiotic therapy is inappropriate. However, consider antibiotic therapy if you suspect a secondary infection of the lesion.
Black widow spider. Several Latrodectus species in North America are known as black widow spiders, although their native territories have considerable overlap. Latrodectus hesperus is primarily found in the West, Latrodectus mactans in the Southeast, and Latrodectus variolus in the Northeast. Unless one is close enough to observe the small differences in the shape of the red or red-orange mark on the ventral abdomen, these spiders are essentially identical and may be considered together as a group. L hesperus has the most characteristic hourglass-shaped mark, L mactans has an anvil-shaped mark, and L variolus has 2 red blobs.
Black widow spiders are found typically in garages, barns, sheds, and woodpiles and on outdoor furniture and classically in outhouses. Female black widow spiders have shiny, black, globular bodies about 1 cm in diameter. They are usually seen hanging ventral side-up from their webs. Male black widow spiders, which are a fraction of the size of their female counterparts, have smaller fangs that cannot penetrate human skin.
Common popular myth holds that female black widow spiders always consume the male spiders after mating. This behavior has been observed more commonly in laboratory conditions than in the wild; thus, it may be stress-induced, and its incidence varies between species within the Latrodectus genus.
Clinical features. Persons who are bitten by a black widow spider may feel a sharp pinprick or nothing at all. The a-latrotoxin in the venom causes uncontrolled release of acetylcholine and norepinephrine(Drug information on norepinephrine) neurotransmitters from presynaptic sites, resulting in painful muscle cramping and signs of adrenergic excess.
Patients often complain of moderate to severe pain that spreads from the bite area and may become generalized.5,6 Bites on the arm or neck may thus present with chest pain; those on the leg or perineum may present with back or lower abdominal pain. Because of the involuntary muscular spasm, diaphoresis, and hypertension associated with severe envenomations, black widow bites can be mistaken for an acute abdomen or myocardial infarction.7
Classically, a target lesion appears at the site of a black widow spider bite that consists of a small patch of pallor (about the size of a dime [approximately 15 mm]), caused by intense local vasoconstriction, surrounded by a rim of erythema.6 One or 2 puncture marks may be seen in the center of the lesion.
The signs and symptoms of black widow spider envenomation typically wax and wane over 24 to 48 hours. During this time, clinicians can mistakenly assume that their interventions were successful, when in fact the patient’s symptoms resolved on their own.5 Prematurely discharged patients who are given an inadequate supply of analgesics often return for evaluation when their symptoms recur. In some cases, symptoms can last several days.8 Although black widow spider bites can be painful and distressing, death is exceedingly rare.
Management. Patients who present with black widow spider bites may be treated with supportive and symptomatic care. Intravenous opiate analgesia, with or without benzodiazepines, is usually sufficient. In a study of 163 patients, intravenous calcium gluconate(Drug information on calcium gluconate) showed no benefit.6
Treatment of systemic latrodectism with black widow spider antivenin remains controversial. The currently available antivenin greatly shortens the duration of symptoms and prevents their recurrence; however, it is associated with a small risk of allergic reactions.6 In the United States, the last reported death related to black widow spider envenomation resulted from anaphylaxis to the antivenin. In this case, the patient had a history of significant obstructive pulmonary disease, which is generally considered a contraindication to serotherapy.9
Although inherently no more dangerous than other commonly used horse serum-derived antivenins (eg, Crotaline snake antivenin), the black widow spider antivenin has been used infrequently in the United States over the past several years, probably because of concerns about its safety profile. The decision to use black widow spider antivenin hinges on your assessment of the therapy’s potential benefit and risks as well as the severity of the patient’s illness.
