A 64-year-old man who recently moved to the area comes to the office for a new patient evaluation. He has chronic low back pain, resulting from an injury 8 years ago, for which he uses several over-the-counter analgesics. Most recently, the patient has been taking naproxen daily. He has no other joint pain, fever, rash, urinary symptoms, or other medical conditions. Blood pressure is 135/70 mm Hg and pulse is 78/min. Examination shows trace lower extremity edema. Neurologic and musculoskeletal examinations reveal 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?

Question

A 64-year-old man who recently moved to the area comes to the office for a new patient evaluation.  He has chronic low back pain, resulting from an injury 8 years ago, for which he uses several over-the-counter analgesics.  Most recently, the patient has been taking naproxen daily.  He has no other joint pain, fever, rash, urinary symptoms, or other medical conditions.  Blood pressure is 135/70 mm Hg and pulse is 78/min.  Examination shows trace lower extremity edema.  Neurologic and musculoskeletal examinations reveal 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?

Quizplus · Accepted Answer

11ec160b_3a40_0cf0_9249_7fb62112225e_MD0001_00 NSAIDs concentrate in the renal medulla along the medullary osmotic gradient, with higher levels in the papillae. These drugs uncouple oxidative phosphorylation and increase oxidative stress, resulting in damage to tubular and vascular endothelial cells. Prolonged use results in chronic interstitial nephritis visualized as patchy interstitial inflammation with subsequent tubular atrophy and fibrosis, papillary necrosis, and scarring. Grossly, the kidneys appear shrunken with irregular contours and distortion of the caliceal architecture. NSAIDs also decrease prostaglandin synthesis, causing renal vasoconstriction which further increases the risk of ischemic papillary necrosis. (Choice B) Chronic pyelonephritis can also cause chronic interstitial nephritis with papillary necrosis. However, urinalysis would be expected to demonstrate evidence of infection (eg, bacteria, nitrites, marked pyuria), and the patient would likely have flank pain and fever. (Choice C) Acute crystal nephropathy presents with renal failure, and patients often have nausea, vomiting, or flank pain. Chronic crystalline nephropathy is most commonly seen in patients with gout or hyperuricemia secondary to urate deposition in the medullary interstitium. (Choice D) Focal segmental glomerular sclerosis (FSGS) presents with nephrotic-range proteinuria. Drug-related secondary FSGS has been reported with the use of anabolic steroids or heroin but not NSAIDs. (Choice E) Ischemic tubular necrosis usually occurs acutely after a prolonged period of hypotension (eg, sepsis, major surgery); muddy brown casts would be expected on urinalysis. (Choice F) Symptoms of renal artery stenosis include resistant hypertension, recurrent flash pulmonary edema, and chronic kidney disease. The absence of hypertension and history of NSAID use are more consistent with chronic interstitial nephritis. Educational objective: Analgesic nephropathy is a form of chronic kidney disease caused by prolonged, heavy intake of nonsteroidal anti-inflammatory drugs and/or acetaminophen. Pathologic characteristics include chronic interstitial nephritis and papillary necrosis.

A 64-Year-Old Man Who Recently Moved to the Area Comes