A 32 year-old woman with no past medical history presented to the emergency department with a 2 day history of a painless, rapidly expanding lesion on her back. She first noticed the lesion 2 days prior but did not recall any trauma or other inciting factors. The woman denied headache, shortness of breath, chest pain, nausea, vomiting, diarrhea or dysuria, but she reported subjective fever and malaise for 2 days. She was not taking any medications, she drank alcohol socially, and she denied intravenous drug use. She worked as an accountant in New York City and traveled frequently to a vacation home in Montauk, Long Island. Immediate Assessment and Management
On presentation to the emergency department, the patient was well appearing and in no apparent distress. Vital signs were: blood pressure, 102/52 mm Hg; pulse, 92 beats/min; respiratory rate,16 breaths/min; tympanic temperature, 98.7°F (37.1°C); and oxygen saturation, 100% on room air. A complete physical examination was entirely within normal limits, except for her skin examination. This was notable for a solitary 9 cm annular plaque on the upper back with central hemorrhagic crust overlying a 5 cm violaceous plaque surrounded by a ring of erythema (Fig. CS10–1). The lesion was only mildly tender to palpation, and there was no underlying fluctuance. What Is the Differential Diagnosis?
The only remarkable finding in this patient is the 2 day old skin lesion, associated with subjective fever and malaise. The differential diagnosis includes infectious diseases such as cellulitis or a bacterially superinfected cyst or arthropod bite, sporotrichosis, lyme disease, and anthrax (Chap. 133); drug reactions such as a fixed-drug eruption, or given the necrotic appearance of the lesion, necrosis due to warfarin or heparin therapy (Chaps. 18 and 60); and necrotic spider bites (Chap. 118). Immediate Assessment and Management
A more detailed history failed to reveal any clues. The woman specifically denied knowledge of tick or spider bites, and she neither worked, lived, nor vacationed in an area known to be inhabited by brown recluse spiders. However, she frequented an area of Long Island where ticks are endemic. An intravenous line was inserted and a complete blood count, basic metabolic panel, and liver function tests were sent; all were within normal limits. The patient was started on vancomycin to provide Staphylococcus aureus and methicillin-resistant S. aureus coverage for a presumed bacterial infection or necrotizing soft tissue infection.
Cases such as these require an immediate assessment for potential public health implications. Once a diagnosis of cutaneous anthrax is considered, the possibility of malicious exposure mandates a coordinated effort to establish a definitive diagnosis. It is important to recall that one of the cases of cutaneous anthrax that occurred following the malicious letters in New York in 2001 involved the case of a small child who was initially diagnosed with brown recluse spider envenomation. Additionally, while spider envenomation may occur outside of regions considered to be endemic as movement of spiders in suitcases, packages, or vehicles may occasionally occur, a new pattern of envenomation may represent a local infestation or the expansion of an endemic area resulting from climate changes. All of these scenarios may require public health interventions. What Further Diagnostic and Therapeutic Interventions Are Indicated?
A dermatology consult was called, and a biopsy was taken for histologic evaluation of a permanent section as well as Gram stain. An acid-fast bacillus stain was also done on the tissue for mycobacterial infection and was negative. Extensive laboratory testing was ordered to help exclude uncommon etiologies for the skin lesion. The biopsy demonstrated epidermal necrosis and dermal abscess, which are nonspecific findings. A wound Gram stain and culture failed to show white blood cells or microorganisms. Case Resolution
Serologies including a Lyme western blot, Rocky Mountain spotted fever antibodies, and Francisella tularensis were all negative. The vancomycin was stopped, and the woman was discharged on a 21 day course of oral doxycycline for presumed Lyme disease given the history and morphology of the lesion. The lesion began to regress on oral doxycycline. Although a final diagnosis was never established, the working diagnosis was that of either Lyme disease or a necrotic spider envenomation, and the patient’s Lyme Western blot was to be repeated in 3 to 4 weeks in order to further clarify between the two leading diagnoses: Lyme or necrotic spider envenomation.