Increase permeability of the glomerular capillary wall leads to massive proteinuria and hypoalbuminemia.
Podocyte injury or genetic mutations of genes producing podocyte proteins may cause nephrotic-range proteinuria.
There are immune and nonimmune insults to the podocyte that lead to:
foot process effacement
decrease in number of functional podocytes
altered slit diaphragm integrity
The end result is increased protein leakiness across the glomerular capillary wall into the urinary space.
Role of the immune system
Minimal change nephrotic syndrome (MCNS) may occur after viral infections and allergen challenges.
MCNS has also been found to occur in children with Hodgkin lymphoma and T-cell lymphoma.
Immunosuppression occurs with drugs such as corticosteroids and cyclosporine provides indirect additional evidence that the immune system contributes to the overall pathogenesis of the nephrotic syndrome.
Clinical Consequences
1. Edema
Underfill theory
It is based on nephrotic-range proteinuria that leads to ↓ plasma protein level with a corresponding ↓ in intravascular oncotic pressure.
This leads to leakage of plasma water into the interstitium, generating edema.
As a result of ↓ intravascular volume, there is ↑ secretion of vasopressin and atrial natriuretic factor, which, along with aldosterone, results in ↑ sodium and water retention by the tubules.
Sodium and water retention therefore occur as a consequence of intravascular volume depletion.
This hypothesis does not fit the clinical picture of some patients with edema caused by nephrotic syndrome who have clinical signs of intravascular volume overload, not volume depletion.
Treating these patients with albumin alone may not be sufficient to induce a diuresis without the concomitant use of diuretics.
Overfill theory
This postulates that nephrotic syndrome is associated with primary sodium retention, with subsequent volume expansion and leakage of excess fluid into the interstitium.
The epithelial sodium channel in the distal tubule may play a key role in sodium reabsorption in nephrotic syndrome.
The clinical weaknesses of this hypothesis are evidenced by the numerous nephrotic patients who present with an obvious clinical picture of intravascular volume depletion: low blood pressure, tachycardia, and elevated hemoconcentration.
Furthermore, amiloride, an epithelial sodium channel blocker, used alone is not sufficient to induce adequate diuresis.
The goal of therapy should be a gradual reduction of edema with judicious use of diuretics, sodium restriction, and cautious use of intravenous albumin infusions, if indicated.
2. Hyperlipidemia
Increase in cholesterol, triglycerides, low-density lipoproteins, and very-low-density lipoproteins.
High-density lipoprotein level remains unchanged or is low.
In adults, this results in an ↑ in the adverse cardiovascular risk ratio, although the implications for children are not as serious, especially those with steroid-responsive nephrotic syndrome.
Hyperlipidemia is thought to be the result of increased synthesis as well as decreased catabolism of lipids.
Although commonplace in adults, the use of lipid-lowering agents in children is uncommon.
3. Increased susceptibility to infections
Susceptible to infections such as cellulitis, spontaneous bacterial peritonitis, and bacteremia.
This occurs as a result of many factors, particularly hypoglobulinemia as a result of the urinary losses of immunoglobulin (Ig) G.
Urinary loss of complement factors (predominantly C3 and C5) → defects in the complement cascade & alternative pathway factors B and D → impaired opsonization of microorganisms.
Significantly increased risk for infection with encapsulated bacteria and, in particular, pneumococcal disease.
Spontaneous bacterial peritonitis
presents with fever, abdominal pain, and peritoneal signs.
Although Pneumococcus is the most frequent cause of peritonitis, Gram-negative bacteria also are associated with a significant number of cases.
Peritoneal leukocyte counts > 250 cells/µL are highly suggestive of spontaneous bacterial peritonitis.
4. Hypercoagulability
Hypercoagulable state resulting from multiple factors:
vascular stasis from hemoconcentration and intravascular volume depletion
increased platelet number and aggregability
changes in coagulation factor levels
There is an ↑ in hepatic production of fibrinogen along with urinary losses of antithrombotic factors such as antithrombin III and protein S.
DVT may occur in any venous bed, including the cerebral venous sinus, renal vein, and pulmonary veins.
The clinical risk is low in children (2–5%) compared with adults but has the potential for serious consequences.
Idiopathic Nephrotic Syndrome
Introduction
Idiopathic nephrotic syndrome is associated with primary glomerular disease without an identifiable causative disease or drug.
Approximately 90% of children with nephrotic syndrome have idiopathic nephrotic syndrome.
Includes multiple histologic types:
minimal change disease
mesangial proliferation
focal segmental glomerulosclerosis
membranous nephropathy
membranoproliferative glomerulonephritis
Pathology
Minimal change nephrotic syndrome (MCNS)
Σ85% of total cases of nephrotic syndrome in children.
The glomeruli appear normal or show a minimal increase in mesangial cells and matrix.
Immunofluorescence microscopy: negative
Electron microscopy: simply reveals effacement of the epithelial cell foot processes
More than 95% of children with minimal change disease respond to corticosteroid therapy.
Mesangial proliferation
Light microscopy: characterized by a diffuse increase in mesangial cells and matrix
Immunofluorescence microscopy: might reveal trace to 1+ mesangial IgM and/or IgA staining
Electron microscopy: reveals increased numbers of mesangial cells and matrix as well as effacement of the epithelial cell foot processes.
Approximately 50% of patients with this histologic lesion respond to corticosteroid therapy.
Focal segmental glomerulosclerosis (FSGS)
Glomeruli show lesions that are both focal (present only in a proportion of glomeruli) and segmental (localized to ≥ 1 intraglomerular tufts).
Light microscopy: lesions consist of mesangial cell proliferation and segmental scarring.
Immunofluorescence microscopy: is positive for IgM and C3 staining in the areas of segmental sclerosis.
Electron microscopy: demonstrates segmental scarring of the glomerular tuft with obliteration of the glomerular capillary lumen.
May be seen secondary to HIV infection, vesicoureteral reflux, and intravenous use of heroin and other drugs of abuse.
Only 20% of patients with FSGS respond to prednisone.
The disease is often progressive, ultimately involving all glomeruli with end-stage renal disease in most patients.
Minimal Change Nephrotic Syndrome
Epidemiology
More common in males than in females (2:1).
Most commonly appears between the ages of 2-6 yrs.
MCNS is present in 85–90% of patients < 6 yr of age.
In contrast, only 20–30% of adolescents who present for the first time with nephrotic syndrome have MCNS.
The more common cause of idiopathic nephrotic syndrome in this older age-group is FSGS.
FSGS is the most common cause of end-stage renal disease in adolescents.
Clinical manifestations
May follow minor infections and, uncommonly, reactions to insect bites, beestings, or poison ivy.
Mild edema (periorbital, lower limbs)
Can initially be misdiagnosed as an allergic disorder because of the periorbital swelling that decreases throughout the day.
With time, the edema becomes generalized.
Differential diagnosis of marked edema:
protein-losing enteropathy
hepatic failure
heart failure
acute or chronic glomerulonephritis
protein malnutrition
Ascites
Pleural effusions
Genital edema
Anorexia
Irritability
Abdominal pain
Diarrhea
Important features of MCNS are the absence of hypertension and gross hematuria (the so-called nephritic features).
Diagnosis
confirmed by urinalysis
urinalysis reveals 3+ or 4+ proteinuria
microscopic hematuria is present in 20% of children
urine protein:creatinine ratio
first morning
spot urine protein:creatinine ratio should be > 2.0
serum electrolytes
blood urea nitrogen
creatinine
usually normal
but may be abnormally elevated if there is diminished renal perfusion from contraction of the intravascular volume
albumin
serum albumin level is <2.5 g/dL
cholesterol levels
serum cholesterol and triglyceride levels are elevated
TRO secondary forms of nephrotic syndrome (children ≥ 10 yr):
complement C3 level
serum complement levels are normal
antinuclear antibody
double-stranded DNA
hepatitis B and C and HIV (in high-risk populations)
kidney biopsy
for children ≥ 12 yr, who are less likely to have MCNS
not routinely performed if the patient fits the standard clinical picture of MCNS
Treatment
Treat as outpatient for children with first episode of nephrotic syndrome and mild to moderate edema.
Such outpatient management is not practiced in all major centers, because the time required for successful education of the family regarding all aspects of the condition can require a short period of hospitalization.
Parent's education:
Must be able to recognize the signs and symptoms of the complications of the disease
Must be taught how to use a dipstick and interpret the results to monitor for the degree of proteinuria.
Tuberculosis must be ruled out prior to starting immunosuppressive therapy with corticosteroids.
by placing a purified protein derivative or obtaining an interferon release assay, and confirming a negative result.
Renal biopsy
Children with onset of uncomplicated nephrotic syndrome between 1 and 8 yr of age are likely to have steroid-responsive MCNS, and steroid therapy may be initiated without a diagnostic renal biopsy.
Children with features that make MCNS less likely (gross hematuria, hypertension, renal insufficiency, hypocomplementemia, or age < 1 yr or > 12 yr) should be considered for renal biopsy before treatment.