An 8-year-old boy is brought to the office due to acute facial puffiness. His mother reports that for the preceding 24 hours he has been easily fatigued and has had dark urine. The patient was treated for a skin infection 3 weeks ago but has no chronic medical conditions. Temperature is 36.1 C (97 F) and blood pressure is 140/94 mm Hg. Physical examination shows periorbital edema and mild pitting edema along the ankles. The remainder of the examination shows no abnormalities. A representative renal biopsy sample is shown in the below image. The fluorescent areas on the slide most likely indicate the presence of which of the following substances?

Question

An 8-year-old boy is brought to the office due to acute facial puffiness.  His mother reports that for the preceding 24 hours he has been easily fatigued and has had dark urine.  The patient was treated for a skin infection 3 weeks ago but has no chronic medical conditions.  Temperature is 36.1 C (97 F) and blood pressure is 140/94 mm Hg.  Physical examination shows periorbital edema and mild pitting edema along the ankles.  The remainder of the examination shows no abnormalities.  A representative renal biopsy sample is shown in the below image.  The fluorescent areas on the slide most likely indicate the presence of which of the following substances?

Quizplus · Accepted Answer

11ec160b_3796_7038_9249_21756d5a9dca_MD0001_00 This pediatric patient with nephritic syndrome (eg, periorbital edema, hematuria, hypertension) following a recent skin infection most likely has poststreptococcal glomerulonephritis (PSGN). PSGN is the most common cause of nephritic syndrome in children and typically occurs 2-4 weeks after exposure to group A beta-hemolytic Streptococcus (eg, pharyngitis, skin infection). Antigens expressed on nephritogenic streptococcal species combine with antibodies to form immune complexes, which are deposited on the glomerular basement membrane (GBM) and induce complement activation and inflammation. These immune complexes are visible on immunofluorescence microscopy as granular deposits of IgG, IgM, and C3 on the GBM and mesangium, producing a "starry sky" appearance. Electron microscopy can show the immune deposits as discrete, electron-dense, subepithelial humps on the GBM. The classic light microscopy finding in PSGN is enlarged, diffusely hypercellular glomeruli due to leukocyte infiltration (neutrophils and monocytes) and mesangial and endothelial cell proliferation. Laboratory studies show decreased serum complement (eg, C3) due to consumption, and elevated titers of streptococcal antibodies (eg, anti-DNAse B, antihyaluronidase, antistreptolysin O [ASO, which is typically elevated with pharyngitis but often undetectable after skin infections]). (Choice A) Disruption of the GBM in PSGN causes increased filtration of proteins such as albumin, which are lost in urine and do not deposit in the GBM. The loss of albumin results in decreased plasma oncotic pressure and subsequent peripheral edema. (Choice B) Complement activation in PSGN occurs primarily via the alternative and lectin pathways, resulting in glomerular C3 deposition without significant C1 or C4 deposits. Subendothelial C1q deposits are characteristic of type 1 membranoproliferative GN. (Choice D) Fibrin deposits are found in rapidly proliferative (crescentic) GN. (Choice E) IgE deposits are sometimes seen in lupus nephritis and are confined to the capillary wall. These are associated with a poorer prognosis. (Choice F) M protein is a component of the streptococcal cell wall that acts as an antiphagocytic virulence factor. The cross-reactivity of antibodies directed against M protein within myocardial cells may be responsible for rheumatic heart disease. However, M protein has not been isolated in the immune complexes in PSGN. Educational objective: Poststreptococcal glomerulonephritis is most common in children and presents with nephritic syndrome (eg, renal failure, hypertension, hematuria with red blood cell casts) 2-4 weeks after an infection with group A beta-hemolytic Streptococcus. Immunofluorescence microscopy shows granular deposits of IgG, IgM, and C3 in the mesangium and basement membranes.

An 8-Year-Old Boy Is Brought to the Office Due to Acute