A 60-year-old man is hospitalized with multiple generalized tonic-clonic seizures. The patient is a heavy alcohol user and has had previous hospitalizations for alcohol withdrawal and alcohol-related seizures. On the second day of hospitalization, temperature is 37.1 C (98.8 F), blood pressure is 155/92 mm Hg, pulse is 108/min, and respirations are 14/min. Examination shows no abnormalities. Laboratory studies are shown below: Urine microscopy shows white blood cells 2-5/hpf, red blood cells 0-1/hpf, and some epithelial cells. Which of the following is the most likely cause of this patient's renal dysfunction?

Question

A 60-year-old man is hospitalized with multiple generalized tonic-clonic seizures.  The patient is a heavy alcohol user and has had previous hospitalizations for alcohol withdrawal and alcohol-related seizures.  On the second day of hospitalization, temperature is 37.1 C (98.8 F), blood pressure is 155/92 mm Hg, pulse is 108/min, and respirations are 14/min.  Examination shows no abnormalities.  Laboratory studies are shown below:  Urine microscopy shows white blood cells 2-5/hpf, red blood cells 0-1/hpf, and some epithelial cells.  Which of the following is the most likely cause of this patient's renal dysfunction?

Quizplus · Accepted Answer

11ec25c8_d4fb_a124_bc81_3daca0a0229d_MD0003_00 This patient with renal insufficiency and discordant blood findings on urine testing (eg, positive blood on urinalysis with negative red blood cells [RBCs] on urine microscopy) following recent tonic-clonic seizures likely has rhabdomyolysis. Rhabdomyolysis involves large-scale skeletal muscle necrosis that can result from crush injury, ischemia, direct toxicity, or in the case of seizures, overexertion from intense and prolonged muscle contraction. A key component of rhabdomyolysis is the release of myoglobin, a skeletal muscle O₂-storage protein that contains heme pigment, into the bloodstream. In the kidneys, myoglobin is degraded and releases heme into the renal tubules; this can cause renal tubular obstruction and tubular epithelial cell injury, resulting in acute tubular necrosis (eg, renal insufficiency). Potassium and phosphorus are also released from lysed muscle cells, causing hyperkalemia and hyperphosphatemia. Discordance between urinalysis (rapid dipstick) and urine microscopy blood findings is useful in recognizing rhabdomyolysis. The blood component of urinalysis detects heme rather than actual RBCs. Therefore, myoglobinuria due to rhabdomyolysis leads to positive blood on urinalysis (due to the presence of heme from myoglobin degradation) in the absence of RBCs on urine microscopy; by contrast, true hematuria leads to positive blood on urinalysis and presence of RBCs on urine microscopy. (Choice A) Acute interstitial nephritis involves renal inflammation, typically evidenced by positive leukocyte esterase on urinalysis and elevated white blood cells (WBCs) with WBC casts on urine microscopy. This patient's urine WBCs are within normal limits. (Choice B) Glomerulonephritis is characterized by RBCs passing through the glomerular membrane to cause true hematuria; dysmorphic RBCs and RBC casts are expected on urine microscopy. (Choice C) Hepatorenal syndrome can occur in patients with advanced liver disease. It results from vasoconstriction of renal arterioles, causing prerenal injury with an expected blood urea nitrogen/creatinine ratio >20. Positive blood is not expected on urinalysis. (Choice D) Nephrolithiasis is a common cause of true hematuria; in addition to positive blood on urinalysis, numerous RBCs are expected on urine microscopy. (Choices E and G) Both urinary tract obstruction (eg, benign prostatic hyperplasia) and renal artery stenosis can cause renal insufficiency; however, rhabdomyolysis is much more likely in this patient given his recent seizure and discordant blood findings on urine testing (which would not been seen with urinary tract obstruction or renal artery stenosis). Educational objective: Skeletal muscle overexertion (eg, due to tonic-clonic seizure) is a potential cause of rhabdomyolysis, which involves the release of myoglobin into the bloodstream and may cause heme-induced acute renal insufficiency. Because urinalysis blood testing detects heme rather than actual red blood cells (RBCs), rhabdomyolysis is often suggested by positive blood on urinalysis in the absence of RBCs on urine microscopy. References: AJKD atlas of renal pathology: myoglobin cast nephropathy. (http://www.ncbi.nlm.nih.gov/pubmed/28115066)

A 60-Year-Old Man Is Hospitalized with Multiple Generalized Tonic-Clonic Seizures