A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 47-year-old woman comes to the emergency department because of worsening pain, discoloration, and swelling of her right hand. Two days ago, she was camping outdoors in Texas with her two young children. She was awoken in the middle of the night by “something crawling on my hand.” The following morning, she saw a wound on her hand that was initially painless, but over the next several hours she noticed reddening and blistering. Yesterday, the lesion turned blue with a blackish discoloration at the center. Her temperature is 38°C (100.4°F), pulse is 83/min, and blood pressure is 128/84 mm Hg. Physical examination shows a bluish plaque with a central area of necrosis surrounded by a rim of erythema at the dorsum of the right hand. Which of the following animals is most likely responsible for the patient's symptoms?
-
A
Diamondback rattlesnakeIncorrect. Rattlesnake bites cause immediate severe pain, swelling, ecchymosis, and systemic coagulopathy - not a delayed painless lesion progressing to necrosis over 48 hours.
-
B
Brown recluse spiderCorrect. Brown recluse spider bites in Texas typically begin painless then evolve over hours-days into a necrotic plaque with the 'red, white, and blue' appearance due to sphingomyelinase D-mediated cytotoxicity.
-
C
Striped bark scorpionIncorrect. Bark scorpion stings cause severe local pain, paresthesias, and neuromuscular agitation (especially in children) but do not produce a progressive necrotic ulcer.
-
D
Deer tickIncorrect. Deer ticks (Ixodes) transmit Lyme disease (erythema migrans - expanding annular rash without central necrosis), babesiosis, and anaplasmosis; they do not cause necrotic cutaneous ulcers.
-
E
Black widow spiderIncorrect. Black widow envenomation produces severe muscle cramping, abdominal rigidity, and autonomic instability from alpha-latrotoxin-induced neurotransmitter release; it does not produce a progressive necrotic skin ulcer.
↑ Tap an answer to reveal the reasoning
Answer: B. A camper in Texas who notices a wound after 'something crawling on her hand,' followed by progression to a painless ulcer, then erythema, blistering, and finally a bluish plaque with central necrosis surrounded by a rim of erythema has been bitten by a brown recluse spider (Loxosceles reclusa). The classic lesion is called 'loxoscelism' or a 'red, white, and blue sign' (central blue/black necrosis, surrounded by white ischemic ring, surrounded by erythematous halo).
Brown recluse venom contains sphingomyelinase D, which lyses cell membranes by hydrolyzing sphingomyelin and activates complement and recruits neutrophils, causing endothelial damage, thrombosis, and progressive cutaneous necrosis. Systemic loxoscelism (rare) can produce hemolysis, DIC, and renal failure. Brown recluse is endemic to the south-central US (Texas, Oklahoma, Arkansas, Missouri).
Diamondback rattlesnake envenomation causes immediate severe pain, swelling, ecchymosis, and coagulopathy - not a delayed painless lesion that necroses over days. Bark scorpion stings cause severe local pain, paresthesias, and in children autonomic and neuromuscular signs (Texas Centruroides) but not progressive necrosis. Deer ticks transmit Lyme disease (erythema migrans, a expanding annular rash without central necrosis), babesiosis, anaplasmosis - none produce this central necrotic plaque. Management of brown recluse bite is supportive: wound care, tetanus prophylaxis, and possibly dapsone for severe lesions.
**Why each option:**
**A.** Rattlesnake bites cause immediate severe pain, swelling, ecchymosis, and systemic coagulopathy - not a delayed painless lesion progressing to necrosis over 48 hours.
**B.** Correct. Brown recluse spider bites in Texas typically begin painless then evolve over hours-days into a necrotic plaque with the 'red, white, and blue' appearance due to sphingomyelinase D-mediated cytotoxicity.
**C.** Bark scorpion stings cause severe local pain, paresthesias, and neuromuscular agitation (especially in children) but do not produce a progressive necrotic ulcer.
**D.** Deer ticks (Ixodes) transmit Lyme disease (erythema migrans - expanding annular rash without central necrosis), babesiosis, and anaplasmosis; they do not cause necrotic cutaneous ulcers.