A 63-Year-Old Man Comes to the Physician Because of Generalized

A 63-year-old man comes to the physician because of generalized fatigue and malaise for 2 months. He has been unable to engage in his daily activities. Three months ago, he was treated for a urinary tract infection with trimethoprim-sulfamethoxazole. He has hypertension, asthma, and chronic lower back pain. Current medications include hydrochlorothiazide, an albuterol inhaler, naproxen, and an aspirin-caffeine combination. Vital signs are within normal limits. Examination shows conjunctival pallor. The remainder of the examination shows no abnormalities. Laboratory results show blood counts within normal limits, blood urea nitrogen of 12 mg/dL, and serum creatinine of 2.0 mg/dL.  Urinalysis reveals 1+ protein and 3-4 white blood cells/hpf.  Renal ultrasound demonstrates bilateral shrunken and irregular kidneys with a few papillary calcifications.  Which of the following is the most likely cause of this patient's renal dysfunction?

A) Chronic interstitial nephritis
B) Chronic pyelonephritis
C) Crystal nephropathy
D) Focal segmental glomerular sclerosis
E) Ischemic tubular necrosis
F) Renal artery stenosis