A 36-year-old woman with chronic back pain is seen in the emergency department with flank pain radiating to the groin and blood in her urine. "This pain is killing me," she says, "and it is quite different from my usual back pain." She has been taking ibuprofen and Percocet (oxycodone/acetaminophen) daily for the past 10 years. She has no fever or dysuria. Her temperature is 36.7 C (98 F), blood pressure is 152/91 mm Hg, pulse is 100/min, and respirations are 14/min. Her mucous membranes are moist and pale. She appears to be in mild distress due to pain. Examination shows right costovertebral tenderness. Laboratory results are as follows: Noncontrast CT of her abdomen and pelvis reveals mild dilation of the right pelvicalyceal system, but no renal calculus is observed. Serum protein electrophoresis and urine Bence Jones proteins are negative. What is the most likely cause of her renal dysfunction?

Question

A 36-year-old woman with chronic back pain is seen in the emergency department with flank pain radiating to the groin and blood in her urine.  "This pain is killing me," she says, "and it is quite different from my usual back pain."  She has been taking ibuprofen and Percocet (oxycodone/acetaminophen) daily for the past 10 years.  She has no fever or dysuria.  Her temperature is 36.7 C (98 F), blood pressure is 152/91 mm Hg, pulse is 100/min, and respirations are 14/min.  Her mucous membranes are moist and pale.  She appears to be in mild distress due to pain.  Examination shows right costovertebral tenderness.  Laboratory results are as follows:  Noncontrast CT of her abdomen and pelvis reveals mild dilation of the right pelvicalyceal system, but no renal calculus is observed.  Serum protein electrophoresis and urine Bence Jones proteins are negative.  What is the most likely cause of her renal dysfunction?

Quizplus · Accepted Answer

Explanation: This patient has symptoms of right ureteric colic with findings of mild pelvicalyceal dilation. This presentation is consistent with acute urinary obstruction due to stones, tumors, or sloughed renal papilla. The CT scan did not reveal the cause of the urinary obstruction, and therefore it is likely that the obstruction was transient and the stone/papilla was passed out in the urine. Unilateral urinary obstruction does not cause acute kidney injury unless it is a solitary kidney. As this patient has a long history of nonsteroidal anti-inflammatory drug (NSAID) intake, it is most likely that analgesic nephropathy is the cause of her renal dysfunction. Analgesic nephropathy is seen in patients with heavy, long-term use of salicylates (aspirin) and acetaminophen with phenacetin or other NSAIDs. A cumulative amount of these analgesics causes chronic tubular injury and tubulointerstitial nephritis that leads to loss of renal function. Ischemic damage to the renal papilla may occur due to vasoconstriction of the vasa recta. Chronic necrosis of the renal papilla with calcification is typically seen. However, sloughing of the papilla may cause hematuria and present acutely as renal colic, as in this patient. Urine studies usually show hematuria, proteinuria, and pyuria with white blood cell casts, whereas the urine culture is usually sterile. The associated microcytic anemia in this patient is out of proportion to the renal dysfunction and is possibly due to gastrointestinal blood loss from NSAID-induced chronic gastric irritation. Discontinuation of the analgesic will cause stabilization or even improvement in renal function. (Choice A) Acute glomerulonephritis presents with elevated creatinine, hypertension, and hematuria with dysmorphic red blood cells (RBCs), RBC casts, and proteinuria. Also, systemic involvement such as arthralgia or rash may be seen. It does not cause flank pain or ureteric colic. (Choice C) Prerenal azotemia occurs due to a decrease in renal perfusion. There is no evidence for hypovolemia in this patient (no history of volume loss and absence of hypotension). (Choice D) Patients with pyelonephritis have flank pain and costovertebral tenderness, but the presentation is not sudden. Fever and dysuria are also commonly observed with pyelonephritis. (Choice E) A unilateral ureteric calculus will not lead to increases in blood urea nitrogen and creatinine levels. Educational objective: Papillary necrosis occurs with heavy long-term use of analgesics such as aspirin, phenacetin, acetaminophen, or other nonsteroidal anti-inflammatory drugs. Nephropathy is usually chronic but may present acutely with hematuria, pyuria, proteinuria, and renal colic. Discontinuation of the analgesic usually results in stabilization or improvement in renal function. References: Analgesic nephropathy. (http://www.ncbi.nlm.nih.gov/pubmed/17410098)

A 36-Year-Old Woman with Chronic Back Pain Is Seen in the Emergency