Nephrotic syndrome (NS) is characterized by persistent heavy proteinuria (mainly albuminuria) (>2 g/m2/24 h);hypoproteinemia (serum albumin <3.0 g/dL); hypercholesterolemia (>250 mg/dL); and edema. Age, race, and geography affect the incidence of NS. Certain HLA types (HLA-DR7, HLA-B8, and HLA-B12) are associated with an increased incidence of NS. Increased glomerular permeability is due to alterations in the normal glomerular cellular and basement membrane barrier that restrict filtration of serum proteins. The resultant massive proteinuria leads to decreased serum proteins, especially albumin. Plasma oncotic pressure is diminished, leading to fluid shifts from vascular to interstitial compartments and plasma volume contraction. Renal syndrome Primary focal Henoch-Schönlein purpura, glomerulosclerosis Wegener and other vasculitides
Membranoproliferative Chronic infections (hepatitis B, glomerulonephritis hepatitis C, malaria, human
Congestive heart failure, constrictive blood flow and the glomerular filtration rate are not usually diminished. Edema results from reduction in effective circulating blood volume and increase in tubular sodium chloride reabsorption secondary to activation of the renin-angiotensin-aldosterone system. Hypoproteinemia stimulates hepatic lipoprotein synthesis and diminishes lipoprotein metabolism, leading to elevated serum lipids (cholesterol, triglycerides) and lipoproteins.
NS may be primary or secondary (Table 162-1). A child with apparent primary NS, prior to renal biopsy, is considered to have idiopathic nephrotic syndrome. Minimal change nephrotic syndrome (MCNS) is the most common histologic form of primary NS in children. More than 80% of children less than 7 years of age with NS have MCNS. Children 7 to 16 years old with NS have a 50% chance of having MCNS. Males are affected more frequently than females (2:1).
Focal segmental glomerulosclerosis (FSGS) accounts for approximately 10% to 20% of children with primary NS. It may present like MCNS or with less impressive proteinuria. FSGS may develop from MCNS or represent a separate entity. A circulating factor that increases glomerular permeability is found in some patients with FSGS. More than 35% of children with FSGS progress to renal failure.
Membranoproliferative glomerulonephritis (MPGN) is characterized by hypocomplementemia with signs of glomerular renal disease. MPGN represents 5% to 15% of children with primary NS, is typically persistent, and has a high likelihood of progression to renal failure over time.
Membranous nephropathy represents less than 5% of children with primary NS. It is seen most commonly in adolescents and children with systemic infections, such as hepatitis B, syphilis, malaria, and toxoplasmosis, or on specific medications (gold, penicillamine).
Congenital NS presents during the first 2 months of life. There are two common types. The Finnish type is an autosomal recessive disorder most common in persons of Scandinavian descent and is due to a mutation in the nephrin protein component in the glomerular filtration slit. The second type is a heterogeneous group of abnormalities, including diffuse mesangial sclerosis and conditions associated with drugs or infections. Prenatal onset is supported by elevated levels of maternal alpha-fetoprotein.
Secondary NS may result from many different causes in children and are listed in Table 162-1.
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