Frequency:
- * In the US: Although various species of Loxosceles are found throughout the world, the L reclusus is found in the United States from the east to the west coast, with predominance in the south.
Mortality/Morbidity:
- * Data regarding mortality rates are not reliable because diagnostic tests to detect brown recluse venom in tissue are not readily available.
* Although deaths have been attributed to presumed brown recluse envenomation, severe outcomes are rare. Typical cases involve only local soft tissue destruction.
* In South America, the more potent venom of the species Loxosceles laeta is responsible for several deaths each year.
Age: Systemic involvement, although uncommon, occurs more frequently in children than in adults.
History:
- * The brown recluse, living up to its name, is naturally nonaggressive toward humans and prefers to live in undisturbed attics, woodpiles, and storage sheds.
* Brown recluses vary in size, and can be up to 2-3 cm in total length. They are most active at night from spring to fall.
* Characteristic violin-shaped markings on their backs have led brown recluses to also be known as fiddleback spiders.
* Envenomation from the brown recluse elicits minimal initial sensation and frequently goes unnoticed until several hours later when the pain intensifies.
* An initial stinging sensation is replaced over 6-8 hours by severe pain and pruritus as local vasospasm causes the tissue to become ischemic.
* Symptoms of systemic loxoscelism are not related to the extent of local tissue reaction and include the following:
. Morbilliform rash
. Fever
. Chills
. Nausea
. Vomiting
. Joint pain
. Hemolysis
. Disseminated intravascular coagulation (DIC)
. Renal failure
. Seizures
. Coma
Physical:
- * Edema around the ischemic bite site produces the appearance of an erythematous halo around the lesion.
. The erythematous margin around the site continues to enlarge peripherally, secondary to gravitational spread of the venom into the tissues.
. Typically, at 24-72 hours, a single clear or hemorrhagic vesicle develops at the site, which later forms a dark eschar (see Picture 1).
* Necrosis is more significant in the fatty areas of the buttocks, thighs, and abdominal wall.
Causes: Dermonecrotic arachnidism has been described in association with several species of Loxosceles spiders, but, in the United States, L reclusus venom is the most potent and the most commonly involved.