A 68-year-old man with newly diagnosed multiple myeloma presents to the emergency department with fatigue, nausea, and a 3-day history of decreased urine output. He started bortezomib-based chemotherapy 5 days ago. Physical examination reveals no edema or signs of volume depletion. Vital signs are stable. Laboratory studies show: serum creatinine 3.2 mg/dL (baseline 0.9 mg/dL), BUN 48 mg/dL, sodium 138 mEq/L, potassium 5.2 mEq/L, calcium 10.2 mg/dL. Urinalysis shows dipstick-positive protein (3+), and urine microscopy reveals granular casts and free light chains. The fractional excretion of sodium (FENa) is 0.8%. Renal ultrasound shows normal-sized kidneys without hydronephrosis. Which of the following is the most likely diagnosis?

1. A)Acute interstitial nephritis from bortezomib hypersensitivity
2. B)Prerenal azotemia from volume depletion
3. C)Light chain cast nephropathy (myeloma kidney)GABARITO
4. D)Contrast-induced nephropathy
5. E)Acute tubular necrosis from sepsis