A 65-year-old man is brought to the emergency department by his caregiver due to confusion. The patient was in his usual state of health last night, but this morning he was found in bed very sleepy and confused. He had also soiled the bed with urine and stool, which he had never done before. The patient had a right middle cerebral artery ischemic stroke a month ago and was recently discharged from a rehabilitation facility. He was treated for pneumonia with oral antibiotics at the rehabilitation facility 2 weeks ago. His other medical issues include hypertension, hyperlipidemia, and benign prostate hyperplasia. Current medications include aspirin, atorvastatin, chlorthalidone, metformin, and tamsulosin. He has no known drug allergies.
Temperature is 37.2 C (99 F), blood pressure is 152/84 mm Hg, pulse is 90/min, and respirations are 18/min. The patient is somnolent and awakens to voice. Mucous membranes are moist. The lungs are clear to auscultation and there are no heart murmurs. The abdomen is soft and nontender. Neurological examination shows residual left hemiparesis from prior stroke.
Laboratory results are as follows:
Serum creatinine was 0.9 mg/dL at hospital discharge a month ago. Calculated urinary fractional excretion of sodium is 0.8%.
Which of the following is the most likely cause of this patient's acute kidney injury?

Question

A 65-year-old man is brought to the emergency department by his caregiver due to confusion.  The patient was in his usual state of health last night, but this morning he was found in bed very sleepy and confused.  He had also soiled the bed with urine and stool, which he had never done before.  The patient had a right middle cerebral artery ischemic stroke a month ago and was recently discharged from a rehabilitation facility.  He was treated for pneumonia with oral antibiotics at the rehabilitation facility 2 weeks ago.  His other medical issues include hypertension, hyperlipidemia, and benign prostate hyperplasia.  Current medications include aspirin, atorvastatin, chlorthalidone, metformin, and tamsulosin.  He has no known drug allergies.
Temperature is 37.2 C (99 F), blood pressure is 152/84 mm Hg, pulse is 90/min, and respirations are 18/min.  The patient is somnolent and awakens to voice.  Mucous membranes are moist.  The lungs are clear to auscultation and there are no heart murmurs.  The abdomen is soft and nontender.  Neurological examination shows residual left hemiparesis from prior stroke.
Laboratory results are as follows:
 Serum creatinine was 0.9 mg/dL at hospital discharge a month ago.  Calculated urinary fractional excretion of sodium is 0.8%.
Which of the following is the most likely cause of this patient's acute kidney injury?

Quizplus · Accepted Answer

11ec193a_96a5_84f7_853d_851db50215bb_MD0002_00 This patient with a recent stroke, who was found confused and incontinent, has developed acute kidney injury (AKI); urinalysis shows 4+ blood in the absence of red blood cells (RBCs). This presentation suggests rhabdomyolysis likely due to seizure. Rhabdomyolysis is characterized by the release of intracellular muscle contents into the circulation after muscular injury; it is common with crush injuries, prolonged muscle activity (eg, seizure, excessive exercise), or drug use (eg, phencyclidine). Positive blood on urine dipstick (a reaction that detects the iron-containing heme pigment in both hemoglobin and myoglobin) in the absence of RBCs (<3/hpf) on microscopic urinalysis suggests myoglobinuria. AKI in rhabdomyolysis typically results from an abundance of filtered heme-pigment leading to acute tubular necrosis; however, the fractional excretion of sodium (FENa) is often unexpectedly low (<1%) despite the intrinsic renal injury that occurs, possibly due to renal vasoconstriction. Hyperkalemia, hyperphosphatemia, and hyperuricemia are predominantly due to muscle cell lysis and are often disproportionate to the degree of renal failure. Markedly elevated serum creatine kinase (often >10,000 U/L) confirms the diagnosis. (Choice A) Like rhabdomyolysis, acute glomerulonephritis often leads to an unexpectedly low FENa in the setting of intrinsic AKI (as does contrast nephropathy). However, dysmorphic RBCs and RBC casts are expected on microscopic urinalysis. (Choice B) Acute interstitial nephritis can trigger hematuria and AKI but generally presents with active urine sediment (eg, RBCs, white blood cells [WBCs], WBC casts), urine eosinophils, fever, and/or rash, as well as an elevated FENa. (Choice D) Acute uric acid nephropathy is usually associated with uric acid crystals on urinalysis and an elevated FENa. Serum uric acid levels are typically significantly higher (>15 mg/dL) than seen in this patient. (Choice E) Rhabdomyolysis may cause some degree of intravascular volume depletion leading to prerenal AKI with FENa <1%. However, this patient's moist mucous membranes, elevated blood pressure, and blood urea nitrogen to creatinine ratio <20:1 make significant volume depletion less likely. FENa is commonly falsely low in rhabdomyolysis, contrast nephropathy, and acute glomerulonephritis. Educational objective: Positive blood on urine dipstick in the absence of red blood cells on microscopic urinalysis suggests myoglobinuria due to rhabdomyolysis. Acute kidney injury typically occurs due to acute tubular necrosis; however, the fractional excretion of sodium is often low despite the mechanism of intrinsic renal injury. Elevated serum creatine kinase (often >10,000 U/L) confirms the diagnosis. __________ References: Acute kidney injury due to rhabdomyolysis. (http://www.ncbi.nlm.nih.gov/pubmed/18711286) Finding the cause of acute kidney injury: which index of fractional excretion is better? (http://www.ncbi.nlm.nih.gov/pubmed/22301562)

A 65-Year-Old Man Is Brought to the Emergency Department by His