A 9-year-old girl is brought to the office due to 2 days of face and eye puffiness. The patient was treated for a rash on her leg with an antibiotic about 3 weeks ago. Temperature is 37.2 C (99 F) and blood pressure is 150/90 mm Hg. On physical examination, there is generalized edema but no rash. Urinalysis reveals proteinuria and hematuria. An electron microscopy image representative of this patient's disease process is shown below: The area marked by the white arrow most likely represents which of the following?

Question

A 9-year-old girl is brought to the office due to 2 days of face and eye puffiness.  The patient was treated for a rash on her leg with an antibiotic about 3 weeks ago.  Temperature is 37.2 C (99 F) and blood pressure is 150/90 mm Hg.  On physical examination, there is generalized edema but no rash.  Urinalysis reveals proteinuria and hematuria.  An electron microscopy image representative of this patient's disease process is shown below:  The area marked by the white arrow most likely represents which of the following?

Quizplus · Accepted Answer

11ec160b_3797_0c7a_9249_0de6f3c4c399_MD0001_00 This pediatric patient with hypertension, hematuria, proteinuria, and edema has a nephritic syndrome. The onset 3 weeks after a bacterial skin infection suggests poststreptococcal glomerulonephritis (PSGN), an immune complex-mediated disease that occurs 2-4 weeks after exposure to group A beta-hemolytic Streptococcus (eg, impetigo, pharyngeal infection). Acute kidney injury is common and leads to fluid and salt retention, often resulting in edema and hypertension. The immune complexes in PSGN are deposited along the glomerular basement membrane (GBM) and are visible on electron microscopy as large, dome-shaped, subepithelial, electron-dense deposits ("humps"). These can be further visualized on immunofluorescence as granular deposits of IgG, IgM, and C3 along the GBM and glomerular mesangium ("lumpy-bumpy" appearance). On light microscopy, the glomeruli are enlarged and hypercellular due to leukocyte infiltration. (Choice A) Proteins such as albumin may be lost in the urine due to increased permeability of the glomerular capillary wall in PSGN. However, albumin does not deposit within the glomerulus or renal tubules. (Choice B) Many antibiotics (eg, penicillins, cephalosporins) can cause acute interstitial nephritis (AIN), which manifests as peritubular T-lymphocyte, monocyte, and eosinophilic infiltration. However edema, significant hematuria, and proteinuria are uncommon, and AIN usually resolves when the offending agent is discontinued. (Choice C) Prominent fibrin deposition is characteristic of rapidly progressive (crescentic) glomerulonephritis. (Choice D) Hyaline, acellular deposits composed of plasma proteins, can be seen in Kimmelstiel-Wilson nodules of diabetic nephropathy. (Choice F) Lipid droplets in renal tubules may be seen in conditions causing nephrotic syndrome, which leads to heavy proteinuria and edema; however, hypertension and hematuria are unexpected. In addition, lipid droplets do not deposit on the basement membrane. (Choice G) Neutrophils and monocytes infiltrate the glomerular mesangium in PSGN, contributing to the hypercellular appearance on light microscopy. Enzymes released from these cells would not typically form extracellular aggregates. Educational objective: Poststreptococcal glomerulonephritis is an immune complex-mediated disease that occurs 2-4 weeks after group A beta-hemolytic Streptococcus infection. Immune complexes composed of IgG, IgM, and C3 are deposited along the glomerular basement membrane and are visible on electron microscopy as large, dome-shaped, subepithelial, electron-dense deposits.

A 9-Year-Old Girl Is Brought to the Office Due to 2