Medical progress: Bites of brown recluse spiders and suspected necrotic arachnidism

Loxosceles spider bites are the only proven medically important cause of necrotic arachnidism in North America, and loxoscelism occurs far less commonly than is perceived by patients or physicians. In patients with verified spider bites, an accurate diagnosis can be made only if the biting spider is identified by an experienced arachnologist An offending spider that is found in an area where loxosceles spiders are not endemic is most likely notloxosceles, and necrosis is unlikely. In rare instances, bites from brown recluse spiders can cause clinically important dermal necrosis and subsequent scarring, but even severe necrosis is rarely life-threatening. Because of the tendency for medical reports to highlight noteworthy extreme cases, physicians may be unaware that the bite of a brown recluse spider is typically self-limited and self-healing, without long-term consequences.⁴⁸ Patients often overemphasize spider involvement in idiopathic wounds, a tendency that can misdirect physicians toward an erroneous diagnosis. Physicians should be skeptical of any undocumented history of a spider bite and should entertain a broad differential diagnosis before attributing a skin ulcer to a spider bite. Misdiagnosis of an ulcer as loxoscelism delays proper treatment, placing the patient at risk. There is no therapy with proven efficacy for loxoscelism. Many questionable treatments have been tried in patients with an unverified diagnosis, and the medical literature on loxoscelism has been obfuscated by misdiagnosed conditions. Both situations have inflated the spectrum of symptomatology, which may partly explain the confusion about therapeutic efficacy. Most practitioners would probably prescribe dapsone in patients with documented loxosceles bites, but even with this therapy, there is marginal evidence to support its use. Dapsone has potentially serious toxicity and should be prescribed judiciously. Other therapies, such as glucocorticoids, hyperbaric oxygen, and early excision, are also of unproven value. In questionable cases, the best approach may be the conservative use of simple first aid and local wound care. Recent advances in medical arachnology are resulting in a reassessment of how to approach patients with suspected necrotic spider bites. With refinement in the epidemiology of loxosceles bites and a greater understanding of the pathophysiology of necrosis, physicians are acquiring the tools to diagnose and treat loxoscelism more effectively.