Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 55-year-old woman presents with diffuse maculopapular rash, fever (38.9°C), and cervical lymphadenopathy 1 week after initiating phenytoin for seizure prophylaxis. Vital signs: BP 128/82, HR 102, RR 18, SpO2 98% on room air. Laboratory studies reveal elevated transaminases (AST 156 U/L), atypical lymphocytes, and eosinophilia (8%). Chest imaging shows no pulmonary involvement. Which pathophysiologic mechanism best explains her drug reaction?
Answer choices
- AType IV hypersensitivity with T-cell-mediated drug reactionCorrect answer
- BDirect hepatotoxicity from phenytoin metabolism
- CType III serum sickness from immune complex deposition
- DType I immediate hypersensitivity with IgE-mediated mast cell activation
- EType II cytotoxic reaction with drug-antibody complex formation
- FType II hypersensitivity with antibody-mediated destruction of drug-metabolizing enzyme complexes
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