Documented cutaneous loxoscelism in the south of France: an unrecognized condition causing delay in diagnosis

Background: Loxoscelism is an envenomation due to a bite by spiders of the genus Loxosceles, very well known on the American continent but unrecognized in Europe.

Case report: We report the case of a 36-year-old woman, without any medical history or treatment, who went to a University Hospital in the South of France, for a painful skin lesion on the internal part of her left thigh, which appeared in the morning and developed rapidly during the day. She was directed to the infectious disease department with a diagnosis of skin infection. In spite of the antibiotics, the lesion increased, with a hemorrhagic central blister, an irregular ecchymotic center, a pale perimeter, and an extensive inflammatory and indurate oedema affecting the whole thigh. There was also a low-grade fever, chills, intense pain and a generalized scarlatiniform exanthema. The lesion was finally diagnosed as cutaneous loxoscelism, then confirmed by collection and identification of a Loxosceles rufescens spider killed by the patient the morning of the occurrence of the lesion. Following an initial symptomatic treatment, the development of a necrotic ulcer justified a delayed surgical reconstruction, after stabilization of the lesion.

Conclusions: Loxosceles bites are usually painless and rarely noticed by patients, often leading to a presumptive diagnosis. Therefore, in the case of a dermonecrotic lesion developing unfavourably with antibiotics, cutaneous loxoscelism should be one of the diagnoses to be considered.