A 76-year-old man comes to the office due to bilateral flank pain and nausea. The patient has not urinated for 24 hours. Medical history is significant for diet-controlled type 2 diabetes and degenerative arthritis of the knee. He occasionally takes naproxen for pain. Temperature is 36.9 C (98.4 F), blood pressure is 140/90 mm Hg, and pulse is 90/min. Cardiopulmonary examination reveals no abnormalities. Abdominal examination shows suprapubic fullness. Mild bilateral costophrenic angle tenderness is present. Laboratory results show a blood urea nitrogen level of 32 mg/dL and creatinine level of 2.6 mg/dL. Four weeks ago, laboratory studies were normal. Which of the following is the most likely cause of this patient's renal dysfunction?

Question

A 76-year-old man comes to the office due to bilateral flank pain and nausea.  The patient has not urinated for 24 hours.  Medical history is significant for diet-controlled type 2 diabetes and degenerative arthritis of the knee.  He occasionally takes naproxen for pain.  Temperature is 36.9 C (98.4 F), blood pressure is 140/90 mm Hg, and pulse is 90/min.  Cardiopulmonary examination reveals no abnormalities.  Abdominal examination shows suprapubic fullness.  Mild bilateral costophrenic angle tenderness is present.  Laboratory results show a blood urea nitrogen level of 32 mg/dL and creatinine level of 2.6 mg/dL.  Four weeks ago, laboratory studies were normal.  Which of the following is the most likely cause of this patient's renal dysfunction?

Quizplus · Accepted Answer

11ec160b_3a52_a9c0_9249_638240eecbad_MD0001_00 This patient with anuria and suprapubic fullness (suggesting a distended bladder) has acute urinary retention (AUR). AUR is characterized by the inability to voluntarily micturate, which leads to suprapubic pain with bladder distension, often palpable above the pelvic brim. As urine refluxes into the ureters and kidneys, dilation of the ureters, renal pelvis, and calyces (hydronephrosis) results in acute kidney injury, bilateral flank pain, and costovertebral angle tenderness. Elevations in creatinine and blood urea nitrogen are also common, but the ratio between the two is variable. Etiologies of AUR include: Bladder outlet obstruction: By far the most common cause of urinary retention, bladder outlet obstructions are precipitated by urethral compression typically due to benign prostatic hyperplasia, particularly in men age >50. Other etiologies include transitional cell carcinoma and rectal or uterine malignancy. Medications: AUR is commonly caused by anticholinergic medications (eg, oxybutynin, atropine) and sympathomimetics (eg, pseudoephedrine). Neurologic dysfunction: Diabetic neuropathy, spinal cord injury, and stroke can result in a neurogenic bladder. (Choice A) Diabetic nephropathy typically presents with proteinuria and chronic kidney disease rather than acute anuria with bilateral flank pain. This patient had normal baseline renal function 4 weeks ago, ruling out chronic kidney disease. (Choice B) Interstitial nephritis sometimes occurs after the introduction of new medications, such as antibiotics or nonsteroidal anti-inflammatory drugs; however, it is often accompanied by fever and rash, neither of which is present in this patient. In additon, although interstitial nephritis can cause impaired urine production (oliguria), an overly distended bladder and flank pain would not be present because impaired urine production would make it difficult to fill the urinary collecting system. (Choices C and D) Ischemia (eg, due to hypotension) can cause tubular necrosis. Abundant protein casts can form in multiple myeloma, leading to obstruction and necrosis of the renal tubules. Both cause intrinsic renal injury with an elevation in creatinine; however, a distended bladder would be unexpected. Educational objective: Acute urinary retention is characterized by anuria and bladder distension and can result in hydronephrosis and acute kidney injury. A palpable, distended bladder is present on examination, and abdominal and flank pain may be present. The most common cause of urinary retention is bladder outlet obstruction (urethral compression) due to benign prostatic hyperplasia. __________ References: Urinary retention in adults: evaluation and initial management. (http://www.ncbi.nlm.nih.gov/pubmed/30277739) Epidemiology and etiology of benign prostatic hyperplasia and bladder outlet obstruction. (http://www.ncbi.nlm.nih.gov/pubmed/24744516)

A 76-Year-Old Man Comes to the Office Due to Bilateral