Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 72-year-old man with no significant past medical history undergoes elective total hip arthroplasty. On postoperative day 3, he develops fever (38.9°C), dyspnea, and a petechial rash. Vital signs are notable for heart rate 118/min, respiratory rate 24/min, and oxygen saturation 88% on room air. Laboratory findings include platelets 65,000/μL, PT 16 seconds (normal 11-13), activated partial thromboplastin time 42 seconds (normal 25-35), D-dimer 2.8 μg/mL (normal <0.5), hemoglobin 9.2 g/dL (baseline 14 g/dL), and creatinine 1.8 mg/dL (baseline 1.0). Chest X-ray demonstrates bilateral infiltrates. Blood cultures are pending. The patient denies recent antibiotic use and has no known drug allergies. Which of the following best explains the pathophysiologic mechanism underlying this clinical presentation?
Answer choices
- AActivation of tissue factor by endotoxin and bacterial components leading to thrombin generation, consumption of platelets and clotting factors, and disseminated fibrin depositionCorrect answer
- BComplement-mediated type II hypersensitivity reaction to orthopedic implant materials with direct antibody binding to prosthetic surface
- CType III hypersensitivity from circulating immune complex deposition in vessel walls with vasculitis and glomerulonephritis
- DDelayed-type hypersensitivity reaction (Type IV) to methylmethacrylate cement with granuloma formation and localized inflammation
- EIgE-mediated mast cell and basophil degranulation triggered by intraoperative antibiotic exposure
- FAcute antibody-mediated rejection of the prosthetic implant with complement-dependent cellular cytotoxicity
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