A 10-year-old boy is brought to the office due to dark brown urine that he first noticed yesterday after swimming practice. Blood pressure is 130/80 mm Hg. Physical examination is normal with the exception of bilateral periorbital edema. Laboratory results are as follows: Which of the following is the most likely diagnosis?

Question

A 10-year-old boy is brought to the office due to dark brown urine that he first noticed yesterday after swimming practice.  Blood pressure is 130/80 mm Hg.  Physical examination is normal with the exception of bilateral periorbital edema.  Laboratory results are as follows:  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec160b_3a42_08c7_9249_413190a64fa3_MD0001_00 This pediatric patient with periorbital edema, hypertension, and hematuria with red blood cell (RBC) casts, as well as mild proteinuria on urinalysis, most likely has poststreptococcal glomerulonephritis, a nonsuppurative complication of a pharyngeal or skin (eg, impetigo) infection. Infection with nephritogenic strains of group A Streptococcus (eg, S pyogenes) can induce formation of antigen-antibody complexes, which are deposited on the glomerular basement membrane. Subsequent activation of complement and inflammation can lead to nephritic syndrome 2-4 weeks after the infection; because of this delay, parents may not report the inciting infection. Urine studies in nephritic syndrome typically reveal RBCs, mild protein, and RBC casts (indicating an intrarenal process). Serum studies show elevated creatinine, antistreptococcal antibodies (from recent infection), and decreased C3 (glomerular complement deposition). Histologic findings include diffusely enlarged hypercellular glomeruli, RBC casts in nephron tubules, and interstitial inflammation and edema. Electron microscopy reveals electron-dense, subepithelial deposits or "humps" along the glomerular basement membrane that represent antigen-antibody complexes. (Choice A) Minimal change disease is the most common cause of pediatric nephrotic syndrome. It is characterized by immune-related loss of the normal glomerular anionic charge (which prevents filtration of negatively charged albumin), leading to heavy proteinuria. However, hematuria and hypertension are unexpected. (Choice B) Nephrolithiasis is a common cause of hematuria; however, the glomeruli are not involved, so RBC casts are unexpected. In addition, nephrolithiasis is rare in children and typically presents with back pain radiating to the groin. (Choice D) Pyelonephritis is most commonly due to an ascending bacterial infection from the bladder. Microscopic urinalysis findings are similar to those of a urinary tract infection (eg, bacteria, leukocytes, nitrites, leukocyte esterase) with the addition of white blood cell casts. (Choice E) Rhabdomyolysis can occur after strenuous exercise and results in muscle pain, elevated creatine kinase levels, and myoglobinuria (ie, positive urine dipstick for blood without RBCs on microscopy). This patient's normal creatine kinase level and the presence of many RBCs on urine microscopy are not suggestive of rhabdomyolysis. Educational objective: Poststreptococcal glomerulonephritis presents most commonly in children with hematuria, hypertension, and periorbital edema. Red blood cell casts and mild proteinuria may be present on urinalysis, and serum creatinine may be elevated.

A 10-Year-Old Boy Is Brought to the Office Due to Dark