Nephrotic Syndrome

Nephrotic Syndrome is a topic covered in the 5-Minute Pediatric Consult.

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Basics

Description

Nephrotic syndrome (NS) is defined by nephrotic-range proteinuria, hypoalbuminemia, edema, and hypercholesterolemia. Nephrotic-range proteinuria is typically found when there is 3 to 4+ protein on the urine dipstick and is defined as >40 mg/m2/h or a spot protein-to-creatinine ratio >2 mg protein/mg creatinine.

Epidemiology

  • Minimal change nephrotic syndrome (MCNS) is the most frequent cause of NS in younger children:
    • Occurs mainly between 2 and 8 years of age, with a peak at 3 years
    • Boys are more commonly affected than girls (3:2).
  • Focal segmental glomerulosclerosis (FSGS) is the 2nd most frequent cause of NS in childhood:
    • Children with FSGS are more likely than children with MCNS to have steroid-resistant nephrotic syndrome (SRNS).
  • Less common than MCNS and FSGS are congenital NS (<3 months) and infantile NS (3 to 12 months).

Prevalence

  • 2 to 7 per 100,000 in children <16 years
  • 16 cases per 100,000 in children <16 years
  • African American and Hispanic children have a higher prevalence of FSGS than Caucasian and Asian children.

Pathophysiology

  • Disruption of podocyte architecture composing the glomerular filtration barrier leads to proteinuria, hypoalbuminemia, and subsequently edema.
  • Hypercholesterolemia occurs due to increased liver production of cholesterol in response to hypoalbuminemia as well as to loss of lipoprotein lipase in urine.
  • MCNS pathology
    • Minimal histologic changes on light microscopy
    • The glomerular tuft size is normal.
    • Mesangial expansion is absent or minimal.
    • Immunofluorescence is usually negative, although mild staining for C3, IgM, and IgA may occasionally be found.
    • Electron microscopy reveals diffuse effacement of the podocyte foot processes.

Etiology

  • Most pediatric cases are primary; 5–10% are secondary to other diseases.
  • The most common primary cause of NS in childhood is MCNS.
  • Other causes of primary NS include FSGS, membranous nephropathy, and membranoproliferative glomerulonephritis (GN).
  • Secondary causes of NS include infections, vasculitis, diabetes, drugs (e.g., NSAIDs), and hereditary disorders.
  • Examples of congenital NS include Finnish type caused by NPHS1 mutations, diffuse mesangial sclerosis (DMS), and infections (toxoplasmosis, rubella, cytomegalovirus, herpes simplex virus, HIV, syphilis).
  • NS can be caused by inherited mutations in proteins involved in the podocyte cytoskeleton, which often results in SRNS and FSGS (up to 20–30% of SRNS).

Commonly Associated Conditions

  • Atopy and MCNS have an association.
  • Syndromes associated with NS include Denys-Drash, nail-patella, Lowe, Galloway-Mowat, Frasier, and Pierson.

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