A 70-year-old woman, whose personal history included a breast cancer operation 14 years earlier, came to the emergency department of another hospital because of severe pain in the lower lip accompanied by swelling and oedema in the lip, chin and submandibular area that had awakened her suddenly at night. She was initially treated with iv corticosteroids and analgesia, and referred home. Four days later, the patient came to the emergency department of our hospital describing that the lesion had become "blackish and yellowish". The lesion was not painful and there was no fever or other accompanying symptoms. On questioning, the patient reported having recently seen spiders in her home. This was in the context of an epidemic of bites by the Loxosceles reclusa spider in the same geographical area. In the previous 15 days, 7 cases of upper and lower limb bites had been diagnosed in the emergency department.
Examination revealed a single lesion of about 2 cm, necrotic in appearance and well demarcated, occupying the lateral third of the skin, vermilion and commissure of the left lower hemilabium, surrounded by a white and purplish halo. Intraorally, a pale mucosal lesion with signs of necrosis and fibrinous exudate was observed in continuity and did not dislodge on scraping. Laboratory tests were ordered, a biopsy was taken and treatment with amoxicillin/clavulanic acid by mouth was started. The infectious diseases department was consulted on suspicion of a spider bite. The differential diagnosis was made with necrotic cutaneous-mucosal lesions, such as cellulitis, vasculitis, diabetic ulcers, vascular insufficiency, drug reactions, thermal or chemical burns, infectious or traumatic, all of which were ruled out. After 7 days, the necrotic tissue was debrided under local anaesthesia. The suggestive clinical and epidemiological context, together with the laboratory and pathological anatomy results and the differential diagnosis, led to the probable diagnosis. At 2 months, given the low aesthetic and functional impact of the scar defect, lip reconstruction was not necessary.