VIOLIN SPIDERS (LOXOSCELES SPECIES)

BACKGROUND

Loxosceles reclusa in a venomous spider more commonly known as the brown recluse, violin spider, or fiddleback spider. As indicated by the common names, the spider has a brown shape/mark resembling a violin or fiddle on the dorsum of its cephalothorax. The Loxosceles genus has a worldwide distribution. The spiders prefer dark areas such as wood piles, crevices between rocks, and basements. While not aggressive, they will bite if antagonized.11

PATHOPHYSIOLOGY

Loxosceles venom is cytotoxic (toxic to living cells) and consists of two main constituents: sphingomyelinase-D and hyaluronidase. Hyaluronidase facilitates the spreading of the venom into tissue while sphingomyelinase-D causes necrosis and hemolysis. Sphingomyelinase also triggers an inflammatory reaction in red blood cells resulting in vessel thrombosis, tissue ischemia, and necrosis.12

CLINICAL MANIFESTATIONS

Loxoscelism will present as an ulcerative lesion, sometimes not until days after the initial envenomation. In general, within several hours after the initial bite there will be local ischemia resulting in pain, pruritus and swelling. A blister or a central area of purple discoloration will form. The venom causes vasoconstriction and can result in a pale border around the central ulcer/blister/discoloration. Over the next several days the ulcer enlarges and the borders demarcate until 1-2 weeks after the initial bite.13

In some cases, systemic loxoscelism can occur. The extent of the cutaneous reaction does not predict the development of systemic loxoscelism, which typically occurs 24 to 72 hours after the envenomation. Young pediatric patients are at greatest risk of reaction. Systemic loxoscelism manifestations include fever, weakness, vomiting, joint pain, petechiae, rhabdomyolysis, disseminated intravascular coagulation, and hemolysis. While rare, severe cases can result in hemoglobinemia, hemoglobinuria, kidney failure, and death.14

TREATMENT

Laboratory testing is not indicated for non-necrotizing local symptoms. Treatment of local symptoms includes wound care, tetanus prophylaxis, analgesics, and antipruritics as necessary. There is no antivenom available. Early excision, intralesional injection of corticosteroids, and dapsone are not indicated. The wound may be confused with a localized abscess, and diagnosis may be made following ineffective incision and drainage or antibiotic treatment. Corrective surgery can be performed after the wound has completed progression and has begun to heal, typically several weeks after the envenomation. Prophylactic antibiotics are not indicated, but should be used as appropriate if a secondary bacterial infection develops.15

Patients with an expanding necrotic lesion or symptoms of systemic loxoscelism should be admitted to a medical facility. A complete blood cell count, urinalysis for blood, metabolic panel, liver function and coagulation studies should be performed. In those patients who develop hemoglobinuria, increased IV fluid hydration can be used to attempt to prevent acute renal failure. Treat significant hemolysis with transfusions, including exchange transfusion in infants and young children with severe systemic loxoscelism.16