USMLE (United States Medical Licensing Examination): Step 1: Basic sciences assessment Practice Exam 25
Practice exam for USMLE (United States Medical Licensing Examination): Step 1: Basic sciences assessment.
Question 1
MEDIUMA 67-year-old man presents to the emergency department with shortness of breath and decreased urine output for 2 days. He was discharged 1 week ago after treatment for a skin infection with an antibiotic. Past medical history includes hypertension and osteoarthritis. Medications include lisinopril and ibuprofen. Temperature is 37.8°C (100.0°F), blood pressure is 148/86 mm Hg, pulse is 96/min, and respirations are 22/min. Examination shows bilateral ankle edema and a faint maculopapular rash on the trunk. Laboratory studies show:
Creatinine: 3.1 mg/dL (reference: 0.6–1.2 mg/dL; baseline 1.0) BUN: 46 mg/dL (reference: 7–20 mg/dL) Eosinophils: 9% (reference: 0–6%) Urinalysis: leukocyte esterase positive, nitrites negative; WBC casts present
Which of the following is the most likely underlying mechanism of this patient’s kidney injury?
This presentation (acute kidney injury after recent antibiotic use, rash, eosinophilia, pyuria with WBC casts) is classic for acute interstitial nephritis, most often a drug reaction. The mechanism is typically a type IV (delayed) hypersensitivity reaction with T-cell–mediated interstitial inflammation. Anti-GBM disease causes hematuria and RBC casts; IgA nephropathy causes episodic hematuria after URI; poststreptococcal GN shows subepithelial humps and low complement; minimal change disease causes nephrotic syndrome with selective albuminuria.
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