Based on the areas of necrosis, the FP suspected that a brown recluse spider bite caused the lesions. He suspected that the whole area of swelling and erythema was the bite reaction, and the 3 ulcerated areas were the regions of necrosis (often there is only 1 central area). The FP considered cellulitis as part of the differential diagnosis and debated whether to prescribe an antibiotic.
While the patient and FP believed that the most likely diagnosis was a spider bite, they were not completely certain of this diagnosis because the patient never saw the spider. Therefore, the patient requested an antibiotic in case this was a bacterial infection. A bacterial culture of the ulcer was performed and the patient was given a 5-day course of oral cephalexin 500 mg 4 times a day.
The FP recommended over-the-counter oral diphenhydramine to be taken around the clock as tolerated along with ibuprofen at mealtimes. The FP kept in contact with the patient by phone and improvement was noted daily. The bacterial culture came back negative, and the lesions all healed with time.
Spider bites can be difficult to diagnose as many lesions are blamed on spiders without evidence of a bite or spider. Conversely, spider bites may be missed as the spider is not typically available for easy identification. To this day, the FP and patient believe these lesions were the work of a brown recluse spider.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Mayeaux, EJ, Usatine R. Pyoderma gangrenosum. In: Usatine R, Smith M, Mayeaux EJ, et al. Color Atlas and Synopsis of Family Medicine. 3rd ed. New York, NY: McGraw-Hill; 2019:1147-1152.
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