Misdiagnosis of brown recluse spider bite

To the editor,

Vetter has a point in claiming that brown recluse spider bite is likely to be overdiagnosed in the United States given that the diagnosis is usually based solely on clinical grounds.¹ His argument that the diagnosis of brown recluse spider bite has frequently been made in areas where Loxosceles reclusa is not naturally found is convincing, and so is the evidence that other spider bites can cause necrotic wounds. I believe that he is correct in recommending caution in implicating brown recluse spiders in idiopathic necrotic wounds in nonendemic areas.

As an illustration of his point, since the 1920s in Brazil and for decades after, the wolf spider (Lycosa raptoria, now Scaptocosa raptoria) was implicated as the major cause of necrotic wounds associated with spider bite. This conclusion was drawn from undocumented clinical observations and from the fact that intradermal inoculation of a high dose of the venom of this spider in rabbit ears leads to local necrosis.^2,3 An antivenin against Lycosa venom was manufactured and used for many years⁴ until the association between necrotic wounds and brown recluse spider bites was observed. Empiric observation accumulated that victims of wolf spider bite did not develop necrosis. Not a single case of local necrosis was observed in a series of 515 patients bitten by wolf spiders who brought in the spider for identification.⁵

The diagnosis of brown recluse spider bite is difficult given that the victims usually overlook the bite. Even when they notice it, they seldom bring in the spider for identification because of its unimpressive appearance. Immunologic diagnosis is not available. The possible differential diagnoses should be considered so that appropriate treatment can be offered. One reason no consensus has been reached on the treatment of brown recluse spider bite is probably that misdiagnosis is common, preventing the correct assessment of the efficacy of different therapies.