She is afebrile and normotensive. Laboratory studies show

A 5-year-old girl has the sudden onset of swelling of her face, hands, legs, and feet 1 week after a viral upper respiratory tract infection. She is afebrile and normotensive. Laboratory studies show:
Serum Albumin 2.0 g/dL
Serum Urea nitrogen 6.0 mg/dL
Serum Creatinine 0.6 mg/dL
Serum Cholesterol 280 mg/dL
Urine protein 4+; 6.0 g/24 h
Which of the following is the most likely diagnosis?

1.Focal glomerulosclerosis
2.Membranous glomerulonephritis
3.Membranoprofilferative glomeriulonphritis
4.Minimal chanage disease
5.Rapidly progressive glomerulonephritis

sol:

The sudden onset of edema in the face and dependent limbs, coupled with hypoalbuminemia suggests a nephrotic syndrome in this child. Consistently, she has hyperlipidemia (cholesterol >200mg) and proteinuria. In children, the most common cause of a nephrotic syndrome is Minimal Change Disease (D, abbrev. MCD).

The child does not exhibit hypertension or overt hematuria. This eliminates renal diseases that are associated with a more NEPHRITIC picture, such as membranoproliferative glomerulonephritis © and Rapidly Progressive GN (E).
Be sure to review NEPHROTIC vs NEPHRITIC syndromes.
MCD, (aka lipoid nephrosis) involves T cell mediated destruction of the polyanion charge barrier on epithelial foot processes, which results in leakage of albumin into the urine. This is manifest in this patient as a reduced serum Albumin (<3.5mg) and Protenuria (>0.15g/24h). While MCD is often idiopathic, it has been described to occur days to weeks after upper respiratory infections, as here.
It is difficult to differentiate between MCD and the other nephrotic choices clinically, but you should know these important distinctions in their histology:
By definition, patients with MCD present histologically with normal looking glomeruli.
Focal segmental Glomerulosclerosis (A, FSGS) presents with focal sclerotic plaques of the glomerular tufts and hyaline deposits. It is also often associated with HIV and IV drug use.
Membranous glomerulonephritis (B) presents later in life, insidiously and is an immune complex disorder that results in mesangial deposits. The workup will show positive Anti nuclear antibodies and/or Anti dsDNA. (remember, this is a NEPHROPATHY and is assoc. with a NEPHROTIC picture despite its name).