Arachnidism by Segestria bavarica with severe neuropathic pain successfully treated with lidocaine 5% plaster

Arachnidism by Segestria bavarica with severe neuropathic pain successfully treated with lidocaine 5% plaster Spider poisoning in Europe is rare, and only a few families within the Araneae order are medically relevant. In particular, spiders of dermatological concern mainly belong to Latrodectus and Loxosceles genus. A 45-year-old woman was referred to us with a large erythematous and edematous indurated plaque with well-defined central pallor on the medial aspect of her right forearm. There were consensual lymphangitis and axillary lymphadenitis (Fig. 1a). Systemic symptoms were not present, and laboratory findings were unremarkable. Intense pain radiated from the bite to her arm, with dysesthesia (burning, tingling, numbness, “electric shock like,” pins and needles sensation), hypoesthesia to touch, and allodynia, causing mild disability on daily activities. She reported that 3 days previously, she suddenly woke up at night with acute severe bite-like pain on the site and found a dead spider without one leg lying in her bed sheet. Within 1 day, a little erythematous and edematous area, centered on two close red dots, appeared with local mild pain. A diagnosis of necrotic spider bite with lymphangitis and severe localized neuropathic pain (LNP) was made (11-point Numeric Rating Scale [NRS]: 8; Neuropathic Pain Diagnostic Questionnaire [DN4]: 7). The patient was treated orally (amoxicillin-clavulanic acid, 1 g bid; prednisone, 25 mg qd) and topically (clobetasol propionate ointment, bid) for 1 week. Because of LNP, lidocaine 5% plaster (10 cm 9 14 cm adhesive plaster, containing 700 mg [5% w/w] lidocaine) once a day for up to 12 hours was applied. After 2 weeks, erythema and edema subsided, and central yellowish eschar with well-defined border was present (Fig. 1b). The patient noticed an improvement in pain (NRS: 4; DN4: 6), which was further improved after another 2 weeks of therapy (NRS 3; DN4 3), when only mild tingling, numbness, and hypoesthesia to touch were present. Two months after the spider bite, she had a small depressed and hypopigmented scar (Fig. 1c) with mild hypoesthesia to touch localized to the surrounding skin. The treatment was then discontinued, without recurrence of pain. The spider found by the patient (Fig. 2) was entomologically identified by the Department of Veterinary Medicine of Perugia University, Italy, as Araneae Labidognatha, Segestriidae: Segestria bavarica Kock, 1843. Spiders of the Segestriidae family are widely present in Europe. They mainly live in holes, between and under stones, or under the tree bark, coming out only for hunting, especially during the night in spring and summer. However, in colder climates they can become synanthropic, and they can also be found in cities. Human attacks are mainly due to Segestria florentina Rossi, 1790, while Segestria bavarica is generally harmless, and no case of arachnidism has ever been reported. Segestriidae rarely induce poisoning, with general symptoms like fever, headache, fatigue, and dizziness, normally resolved in about 1 week. Skin lesions, localized in the bite site, are generally erythematous and edematous, without eschars or scarring outcomes. Skin lesions due to Segestriidae are usually painful; burning sensation and hypoesthesia, suggesting LNP as in our patient, were previously described. Segestriidae venom contains neurotoxins responsible for neuropathic pain. The good result obtained with lidocaine 5% plaster is due to a dual mode of action, by providing a mechanical barrier effect and a pharmacological action via voltage-gated sodium channel blockade as a direct result of lidocaine action. This therapy is successfully