Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 19-year-old previously healthy male college student presents to the emergency department with a 12-hour history of fever (39.8°C), severe frontal headache, and neck stiffness. On examination, he has a petechial rash on his trunk and lower extremities. Vital signs show HR 118 bpm, BP 92/54 mmHg, RR 22/min, SpO2 98% on room air. Laboratory studies reveal WBC 18,500/μL, platelets 35,000/μL, INR 2.8, and D-dimer markedly elevated. CSF analysis shows protein 285 mg/dL, glucose 18 mg/dL, and 8,500 WBC/μL (85% neutrophils). Blood cultures grow gram-negative diplococci identified as Neisseria meningitidis. Despite initiation of ceftriaxone, vancomycin, and aggressive fluid resuscitation, the patient develops worsening hypotension and signs of disseminated intravascular coagulation with ischemic necrosis of distal digits. Which of the following best explains the severe systemic inflammatory response and tissue injury in this patient?
Answer choices
- AType II hypersensitivity reaction with anti-neutrophil cytoplasmic antibodies (ANCA) causing vasculitis of small vessels
- BType III hypersensitivity with immune complex deposition in vessel walls triggering complement-mediated inflammation
- CGram-negative bacterial endotoxin (LPS) activation of TLR4 on macrophages and endothelial cells triggering NF-κB-mediated cytokine stormCorrect answer
- DType IV hypersensitivity with CD8+ T cell-mediated destruction of infected vascular endothelium
- EHereditary complement deficiency (C5) preventing formation of the membrane attack complex against bacterial pathogens
- FDirect bacterial invasion and proliferation within endothelial cells causing mechanical vessel wall rupture
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