The nephrotic syndrome is a renal disorder characterised by heavy urinary protein losses. It is the final clinical presentation of both primary renal pathology and systemic pathologies which affect the kidney.

The nephrotic syndrome is defined by:

• combination of heavy proteinuria (protein: creatinine ratio greater than 200 mg/mmol)
• hypoalbuminemia (less than 25 g/L)
• and generalized oedema
  • particularly periorbital oedema

This triad is commonly accompanied by hyperlipidaemia.

Whilst the definition appears clear, there are a number of points worth consideration:

• with increasing age patients are more vulnerable to severe proteinurea and hypoalbuminaemia
• the level of hypoalbuminaemia at which oedema develops varies between individuals and with age
• other measures of renal function such as urea and creatinine, are usually normal
• renal failure may develop
• although the nephrotic syndrome has long thought to be due to protein loss resulting in a low albumin and low plasma oncotic pressure, patients may have a normal or increased plasma volume (this would suggest that there is not a simple relation between salt retention and renin concentration in many patients (1))

With respect to nephrotic synndrome (NS) in children:

• approximately 80% of cases of childhood NS have minimal change disease (MCD)
• NS is commonest glomerular disease of childhood with a median age at presentation of 4 years
• more common in males than females (ratio 3:2)
  • over 90% of cases with MCD will respond to steroid therapy, but 70% of these will develop a relapsing course
    • steroid responsiveness is the most important determining factor in the long-term prognosis of NS
  • conditions such as focal segmental glomerulosclerosis (FSGS) and mesangiocapillary glomerulosclerosis (MCGN) account for the remaining 20% of cases of NS
    • tend to present in the older child and the majority do not respond to oral steroid therapy alone, making the outcome considerably less
  • assumed that MCD and FSGS are immune mediated; there is controversy as to whether they are part of a spectrum or separate disorders
    • serum IgG levels are low and IgM levels are often raised
  • routine renal biopsy is not performed at presentation
    • this is because the majority of children have MCD and are likely to respond to corticosteroid

• atypical features in a child:

  • age less than 12 months or greater than 12 years
  • persistent hypertension or impaired renal function
  • gross haematuria
  • low plasma C3
  • hepatitis B or C positive

Reference:

• (1) Lancet (1995); 346 (8969):148-52.
• (2) Dolon MN, Gill D. Management of nephrotic syndrome. Paediatrics and Child Health 2002:369-374.