Question of the Week
For January 22, 2019
A 20-year-old male college student presents for evaluation of a rash that developed gradually during the past 3 days. Two weeks ago, he began a 10-day course of amoxicillin for streptococcal pharyngitis. He takes no other medications. His medical history is unremarkable. A paternal uncle has Alport syndrome.
His blood pressure is 140/85 mm Hg, his heart rate is 100 beats per minute, and his temperature is 37.5°C. Physical examination reveals a diffuse, erythematous maculopapular rash, predominantly across the trunk.
Laboratory testing yields the following results:
Leukocyte count (per mm3)
Urea nitrogen (mg/dL)
Complement C3 (mg/dL)
Complement C4 (mg/dL)
The platelet count and leukocyte differential are normal. Urinalysis shows 1+ protein, 1–3 red cells per high-power field (reference range, 0–2), and 10–20 white cells per high-power field (0–2). A Gram stain of the urine specimen is negative.
Renal ultrasonography shows normal-size kidneys without hydronephrosis.
Which one of the following conditions is the most likely explanation for acute kidney injury in this patient?